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Sourcecode: postgresql-8.4 version File versions

pgstat.c

/* ----------
 * pgstat.c
 *
 *    All the statistics collector stuff hacked up in one big, ugly file.
 *
 *    TODO: - Separate collector, postmaster and backend stuff
 *                  into different files.
 *
 *                - Add some automatic call for pgstat vacuuming.
 *
 *                - Add a pgstat config column to pg_database, so this
 *                  entire thing can be enabled/disabled on a per db basis.
 *
 *    Copyright (c) 2001-2009, PostgreSQL Global Development Group
 *
 *    $PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.189 2009/06/11 14:49:01 momjian Exp $
 * ----------
 */
#include "postgres.h"

#include <unistd.h>
#include <fcntl.h>
#include <sys/param.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>
#include <time.h>
#ifdef HAVE_POLL_H
#include <poll.h>
#endif
#ifdef HAVE_SYS_POLL_H
#include <sys/poll.h>
#endif

#include "pgstat.h"

#include "access/heapam.h"
#include "access/transam.h"
#include "access/twophase_rmgr.h"
#include "access/xact.h"
#include "catalog/pg_database.h"
#include "catalog/pg_proc.h"
#include "libpq/ip.h"
#include "libpq/libpq.h"
#include "libpq/pqsignal.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "pg_trace.h"
#include "postmaster/autovacuum.h"
#include "postmaster/fork_process.h"
#include "postmaster/postmaster.h"
#include "storage/backendid.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/pg_shmem.h"
#include "storage/pmsignal.h"
#include "utils/guc.h"
#include "utils/memutils.h"
#include "utils/ps_status.h"
#include "utils/rel.h"
#include "utils/tqual.h"


/* ----------
 * Paths for the statistics files (relative to installation's $PGDATA).
 * ----------
 */
#define PGSTAT_STAT_PERMANENT_FILENAME          "global/pgstat.stat"
#define PGSTAT_STAT_PERMANENT_TMPFILE           "global/pgstat.tmp"

/* ----------
 * Timer definitions.
 * ----------
 */
#define PGSTAT_STAT_INTERVAL  500         /* Minimum time between stats file
                                                             * updates; in milliseconds. */

#define PGSTAT_RETRY_DELAY          10          /* How long to wait between statistics
                                                             * update requests; in milliseconds. */

#define PGSTAT_MAX_WAIT_TIME  5000  /* Maximum time to wait for a stats
                                                             * file update; in milliseconds. */

#define PGSTAT_RESTART_INTERVAL 60        /* How often to attempt to restart a
                                                             * failed statistics collector; in
                                                             * seconds. */

#define PGSTAT_SELECT_TIMEOUT 2           /* How often to check for postmaster
                                                             * death; in seconds. */

#define PGSTAT_POLL_LOOP_COUNT      (PGSTAT_MAX_WAIT_TIME / PGSTAT_RETRY_DELAY)


/* ----------
 * The initial size hints for the hash tables used in the collector.
 * ----------
 */
#define PGSTAT_DB_HASH_SIZE         16
#define PGSTAT_TAB_HASH_SIZE  512
#define PGSTAT_FUNCTION_HASH_SIZE   512


/* ----------
 * GUC parameters
 * ----------
 */
bool        pgstat_track_activities = false;
bool        pgstat_track_counts = false;
int               pgstat_track_functions = TRACK_FUNC_OFF;
int               pgstat_track_activity_query_size = 1024;

/* ----------
 * Built from GUC parameter
 * ----------
 */
char     *pgstat_stat_filename = NULL;
char     *pgstat_stat_tmpname = NULL;

/*
 * BgWriter global statistics counters (unused in other processes).
 * Stored directly in a stats message structure so it can be sent
 * without needing to copy things around.  We assume this inits to zeroes.
 */
PgStat_MsgBgWriter BgWriterStats;

/* ----------
 * Local data
 * ----------
 */
NON_EXEC_STATIC int pgStatSock = -1;

static struct sockaddr_storage pgStatAddr;

static time_t last_pgstat_start_time;

static bool pgStatRunningInCollector = false;

/*
 * Structures in which backends store per-table info that's waiting to be
 * sent to the collector.
 *
 * NOTE: once allocated, TabStatusArray structures are never moved or deleted
 * for the life of the backend.  Also, we zero out the t_id fields of the
 * contained PgStat_TableStatus structs whenever they are not actively in use.
 * This allows relcache pgstat_info pointers to be treated as long-lived data,
 * avoiding repeated searches in pgstat_initstats() when a relation is
 * repeatedly opened during a transaction.
 */
#define TABSTAT_QUANTUM       100 /* we alloc this many at a time */

typedef struct TabStatusArray
{
      struct TabStatusArray *tsa_next;    /* link to next array, if any */
      int               tsa_used;         /* # entries currently used */
      PgStat_TableStatus tsa_entries[TABSTAT_QUANTUM];      /* per-table data */
} TabStatusArray;

static TabStatusArray *pgStatTabList = NULL;

/*
 * Backends store per-function info that's waiting to be sent to the collector
 * in this hash table (indexed by function OID).
 */
static HTAB *pgStatFunctions = NULL;

/*
 * Indicates if backend has some function stats that it hasn't yet
 * sent to the collector.
 */
static bool have_function_stats = false;

/*
 * Tuple insertion/deletion counts for an open transaction can't be propagated
 * into PgStat_TableStatus counters until we know if it is going to commit
 * or abort.  Hence, we keep these counts in per-subxact structs that live
 * in TopTransactionContext.  This data structure is designed on the assumption
 * that subxacts won't usually modify very many tables.
 */
typedef struct PgStat_SubXactStatus
{
      int               nest_level;       /* subtransaction nest level */
      struct PgStat_SubXactStatus *prev;  /* higher-level subxact if any */
      PgStat_TableXactStatus *first;            /* head of list for this subxact */
} PgStat_SubXactStatus;

static PgStat_SubXactStatus *pgStatXactStack = NULL;

static int  pgStatXactCommit = 0;
static int  pgStatXactRollback = 0;

/* Record that's written to 2PC state file when pgstat state is persisted */
typedef struct TwoPhasePgStatRecord
{
      PgStat_Counter tuples_inserted;           /* tuples inserted in xact */
      PgStat_Counter tuples_deleted;            /* tuples deleted in xact */
      Oid               t_id;             /* table's OID */
      bool        t_shared;         /* is it a shared catalog? */
} TwoPhasePgStatRecord;

/*
 * Info about current "snapshot" of stats file
 */
static MemoryContext pgStatLocalContext = NULL;
static HTAB *pgStatDBHash = NULL;
static PgBackendStatus *localBackendStatusTable = NULL;
static int  localNumBackends = 0;

/*
 * Cluster wide statistics, kept in the stats collector.
 * Contains statistics that are not collected per database
 * or per table.
 */
static PgStat_GlobalStats globalStats;

/* Last time the collector successfully wrote the stats file */
static TimestampTz last_statwrite;

/* Latest statistics request time from backends */
static TimestampTz last_statrequest;

static volatile bool need_exit = false;
static volatile bool got_SIGHUP = false;

/*
 * Total time charged to functions so far in the current backend.
 * We use this to help separate "self" and "other" time charges.
 * (We assume this initializes to zero.)
 */
static instr_time total_func_time;


/* ----------
 * Local function forward declarations
 * ----------
 */
#ifdef EXEC_BACKEND
static pid_t pgstat_forkexec(void);
#endif

NON_EXEC_STATIC void PgstatCollectorMain(int argc, char *argv[]);
static void pgstat_exit(SIGNAL_ARGS);
static void pgstat_beshutdown_hook(int code, Datum arg);
static void pgstat_sighup_handler(SIGNAL_ARGS);

static PgStat_StatDBEntry *pgstat_get_db_entry(Oid databaseid, bool create);
static void pgstat_write_statsfile(bool permanent);
static HTAB *pgstat_read_statsfile(Oid onlydb, bool permanent);
static void backend_read_statsfile(void);
static void pgstat_read_current_status(void);

static void pgstat_send_tabstat(PgStat_MsgTabstat *tsmsg);
static void pgstat_send_funcstats(void);
static HTAB *pgstat_collect_oids(Oid catalogid);

static PgStat_TableStatus *get_tabstat_entry(Oid rel_id, bool isshared);

static void pgstat_setup_memcxt(void);

static void pgstat_setheader(PgStat_MsgHdr *hdr, StatMsgType mtype);
static void pgstat_send(void *msg, int len);

static void pgstat_recv_inquiry(PgStat_MsgInquiry *msg, int len);
static void pgstat_recv_tabstat(PgStat_MsgTabstat *msg, int len);
static void pgstat_recv_tabpurge(PgStat_MsgTabpurge *msg, int len);
static void pgstat_recv_dropdb(PgStat_MsgDropdb *msg, int len);
static void pgstat_recv_resetcounter(PgStat_MsgResetcounter *msg, int len);
static void pgstat_recv_autovac(PgStat_MsgAutovacStart *msg, int len);
static void pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len);
static void pgstat_recv_analyze(PgStat_MsgAnalyze *msg, int len);
static void pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len);
static void pgstat_recv_funcstat(PgStat_MsgFuncstat *msg, int len);
static void pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len);


/* ------------------------------------------------------------
 * Public functions called from postmaster follow
 * ------------------------------------------------------------
 */

/* ----------
 * pgstat_init() -
 *
 *    Called from postmaster at startup. Create the resources required
 *    by the statistics collector process.  If unable to do so, do not
 *    fail --- better to let the postmaster start with stats collection
 *    disabled.
 * ----------
 */
void
pgstat_init(void)
{
      ACCEPT_TYPE_ARG3 alen;
      struct addrinfo *addrs = NULL,
                     *addr,
                        hints;
      int               ret;
      fd_set            rset;
      struct timeval tv;
      char        test_byte;
      int               sel_res;
      int               tries = 0;

#define TESTBYTEVAL ((char) 199)

      /*
       * Create the UDP socket for sending and receiving statistic messages
       */
      hints.ai_flags = AI_PASSIVE;
      hints.ai_family = PF_UNSPEC;
      hints.ai_socktype = SOCK_DGRAM;
      hints.ai_protocol = 0;
      hints.ai_addrlen = 0;
      hints.ai_addr = NULL;
      hints.ai_canonname = NULL;
      hints.ai_next = NULL;
      ret = pg_getaddrinfo_all("localhost", NULL, &hints, &addrs);
      if (ret || !addrs)
      {
            ereport(LOG,
                        (errmsg("could not resolve \"localhost\": %s",
                                    gai_strerror(ret))));
            goto startup_failed;
      }

      /*
       * On some platforms, pg_getaddrinfo_all() may return multiple addresses
       * only one of which will actually work (eg, both IPv6 and IPv4 addresses
       * when kernel will reject IPv6).  Worse, the failure may occur at the
       * bind() or perhaps even connect() stage.      So we must loop through the
       * results till we find a working combination. We will generate LOG
       * messages, but no error, for bogus combinations.
       */
      for (addr = addrs; addr; addr = addr->ai_next)
      {
#ifdef HAVE_UNIX_SOCKETS
            /* Ignore AF_UNIX sockets, if any are returned. */
            if (addr->ai_family == AF_UNIX)
                  continue;
#endif

            if (++tries > 1)
                  ereport(LOG,
                  (errmsg("trying another address for the statistics collector")));

            /*
             * Create the socket.
             */
            if ((pgStatSock = socket(addr->ai_family, SOCK_DGRAM, 0)) < 0)
            {
                  ereport(LOG,
                              (errcode_for_socket_access(),
                  errmsg("could not create socket for statistics collector: %m")));
                  continue;
            }

            /*
             * Bind it to a kernel assigned port on localhost and get the assigned
             * port via getsockname().
             */
            if (bind(pgStatSock, addr->ai_addr, addr->ai_addrlen) < 0)
            {
                  ereport(LOG,
                              (errcode_for_socket_access(),
                    errmsg("could not bind socket for statistics collector: %m")));
                  closesocket(pgStatSock);
                  pgStatSock = -1;
                  continue;
            }

            alen = sizeof(pgStatAddr);
            if (getsockname(pgStatSock, (struct sockaddr *) & pgStatAddr, &alen) < 0)
            {
                  ereport(LOG,
                              (errcode_for_socket_access(),
                               errmsg("could not get address of socket for statistics collector: %m")));
                  closesocket(pgStatSock);
                  pgStatSock = -1;
                  continue;
            }

            /*
             * Connect the socket to its own address.  This saves a few cycles by
             * not having to respecify the target address on every send. This also
             * provides a kernel-level check that only packets from this same
             * address will be received.
             */
            if (connect(pgStatSock, (struct sockaddr *) & pgStatAddr, alen) < 0)
            {
                  ereport(LOG,
                              (errcode_for_socket_access(),
                  errmsg("could not connect socket for statistics collector: %m")));
                  closesocket(pgStatSock);
                  pgStatSock = -1;
                  continue;
            }

            /*
             * Try to send and receive a one-byte test message on the socket. This
             * is to catch situations where the socket can be created but will not
             * actually pass data (for instance, because kernel packet filtering
             * rules prevent it).
             */
            test_byte = TESTBYTEVAL;

retry1:
            if (send(pgStatSock, &test_byte, 1, 0) != 1)
            {
                  if (errno == EINTR)
                        goto retry1;      /* if interrupted, just retry */
                  ereport(LOG,
                              (errcode_for_socket_access(),
                               errmsg("could not send test message on socket for statistics collector: %m")));
                  closesocket(pgStatSock);
                  pgStatSock = -1;
                  continue;
            }

            /*
             * There could possibly be a little delay before the message can be
             * received.  We arbitrarily allow up to half a second before deciding
             * it's broken.
             */
            for (;;)                      /* need a loop to handle EINTR */
            {
                  FD_ZERO(&rset);
                  FD_SET            (pgStatSock, &rset);

                  tv.tv_sec = 0;
                  tv.tv_usec = 500000;
                  sel_res = select(pgStatSock + 1, &rset, NULL, NULL, &tv);
                  if (sel_res >= 0 || errno != EINTR)
                        break;
            }
            if (sel_res < 0)
            {
                  ereport(LOG,
                              (errcode_for_socket_access(),
                               errmsg("select() failed in statistics collector: %m")));
                  closesocket(pgStatSock);
                  pgStatSock = -1;
                  continue;
            }
            if (sel_res == 0 || !FD_ISSET(pgStatSock, &rset))
            {
                  /*
                   * This is the case we actually think is likely, so take pains to
                   * give a specific message for it.
                   *
                   * errno will not be set meaningfully here, so don't use it.
                   */
                  ereport(LOG,
                              (errcode(ERRCODE_CONNECTION_FAILURE),
                               errmsg("test message did not get through on socket for statistics collector")));
                  closesocket(pgStatSock);
                  pgStatSock = -1;
                  continue;
            }

            test_byte++;                  /* just make sure variable is changed */

retry2:
            if (recv(pgStatSock, &test_byte, 1, 0) != 1)
            {
                  if (errno == EINTR)
                        goto retry2;      /* if interrupted, just retry */
                  ereport(LOG,
                              (errcode_for_socket_access(),
                               errmsg("could not receive test message on socket for statistics collector: %m")));
                  closesocket(pgStatSock);
                  pgStatSock = -1;
                  continue;
            }

            if (test_byte != TESTBYTEVAL) /* strictly paranoia ... */
            {
                  ereport(LOG,
                              (errcode(ERRCODE_INTERNAL_ERROR),
                               errmsg("incorrect test message transmission on socket for statistics collector")));
                  closesocket(pgStatSock);
                  pgStatSock = -1;
                  continue;
            }

            /* If we get here, we have a working socket */
            break;
      }

      /* Did we find a working address? */
      if (!addr || pgStatSock < 0)
            goto startup_failed;

      /*
       * Set the socket to non-blocking IO.  This ensures that if the collector
       * falls behind, statistics messages will be discarded; backends won't
       * block waiting to send messages to the collector.
       */
      if (!pg_set_noblock(pgStatSock))
      {
            ereport(LOG,
                        (errcode_for_socket_access(),
                         errmsg("could not set statistics collector socket to nonblocking mode: %m")));
            goto startup_failed;
      }

      pg_freeaddrinfo_all(hints.ai_family, addrs);

      return;

startup_failed:
      ereport(LOG,
        (errmsg("disabling statistics collector for lack of working socket")));

      if (addrs)
            pg_freeaddrinfo_all(hints.ai_family, addrs);

      if (pgStatSock >= 0)
            closesocket(pgStatSock);
      pgStatSock = -1;

      /*
       * Adjust GUC variables to suppress useless activity, and for debugging
       * purposes (seeing track_counts off is a clue that we failed here). We
       * use PGC_S_OVERRIDE because there is no point in trying to turn it back
       * on from postgresql.conf without a restart.
       */
      SetConfigOption("track_counts", "off", PGC_INTERNAL, PGC_S_OVERRIDE);
}

/*
 * pgstat_reset_all() -
 *
 * Remove the stats file.  This is currently used only if WAL
 * recovery is needed after a crash.
 */
void
pgstat_reset_all(void)
{
      unlink(pgstat_stat_filename);
      unlink(PGSTAT_STAT_PERMANENT_FILENAME);
}

#ifdef EXEC_BACKEND

/*
 * pgstat_forkexec() -
 *
 * Format up the arglist for, then fork and exec, statistics collector process
 */
static pid_t
pgstat_forkexec(void)
{
      char     *av[10];
      int               ac = 0;

      av[ac++] = "postgres";
      av[ac++] = "--forkcol";
      av[ac++] = NULL;              /* filled in by postmaster_forkexec */

      av[ac] = NULL;
      Assert(ac < lengthof(av));

      return postmaster_forkexec(ac, av);
}
#endif   /* EXEC_BACKEND */


/*
 * pgstat_start() -
 *
 *    Called from postmaster at startup or after an existing collector
 *    died.  Attempt to fire up a fresh statistics collector.
 *
 *    Returns PID of child process, or 0 if fail.
 *
 *    Note: if fail, we will be called again from the postmaster main loop.
 */
int
pgstat_start(void)
{
      time_t            curtime;
      pid_t       pgStatPid;

      /*
       * Check that the socket is there, else pgstat_init failed and we can do
       * nothing useful.
       */
      if (pgStatSock < 0)
            return 0;

      /*
       * Do nothing if too soon since last collector start.  This is a safety
       * valve to protect against continuous respawn attempts if the collector
       * is dying immediately at launch.  Note that since we will be re-called
       * from the postmaster main loop, we will get another chance later.
       */
      curtime = time(NULL);
      if ((unsigned int) (curtime - last_pgstat_start_time) <
            (unsigned int) PGSTAT_RESTART_INTERVAL)
            return 0;
      last_pgstat_start_time = curtime;

      /*
       * Okay, fork off the collector.
       */
#ifdef EXEC_BACKEND
      switch ((pgStatPid = pgstat_forkexec()))
#else
      switch ((pgStatPid = fork_process()))
#endif
      {
            case -1:
                  ereport(LOG,
                              (errmsg("could not fork statistics collector: %m")));
                  return 0;

#ifndef EXEC_BACKEND
            case 0:
                  /* in postmaster child ... */
                  /* Close the postmaster's sockets */
                  ClosePostmasterPorts(false);

                  /* Lose the postmaster's on-exit routines */
                  on_exit_reset();

                  /* Drop our connection to postmaster's shared memory, as well */
                  PGSharedMemoryDetach();

                  PgstatCollectorMain(0, NULL);
                  break;
#endif

            default:
                  return (int) pgStatPid;
      }

      /* shouldn't get here */
      return 0;
}

void
allow_immediate_pgstat_restart(void)
{
      last_pgstat_start_time = 0;
}

/* ------------------------------------------------------------
 * Public functions used by backends follow
 *------------------------------------------------------------
 */


/* ----------
 * pgstat_report_stat() -
 *
 *    Called from tcop/postgres.c to send the so far collected per-table
 *    and function usage statistics to the collector.  Note that this is
 *    called only when not within a transaction, so it is fair to use
 *    transaction stop time as an approximation of current time.
 * ----------
 */
void
pgstat_report_stat(bool force)
{
      /* we assume this inits to all zeroes: */
      static const PgStat_TableCounts all_zeroes;
      static TimestampTz last_report = 0;

      TimestampTz now;
      PgStat_MsgTabstat regular_msg;
      PgStat_MsgTabstat shared_msg;
      TabStatusArray *tsa;
      int               i;

      /* Don't expend a clock check if nothing to do */
      if ((pgStatTabList == NULL || pgStatTabList->tsa_used == 0)
            && !have_function_stats)
            return;

      /*
       * Don't send a message unless it's been at least PGSTAT_STAT_INTERVAL
       * msec since we last sent one, or the caller wants to force stats out.
       */
      now = GetCurrentTransactionStopTimestamp();
      if (!force &&
            !TimestampDifferenceExceeds(last_report, now, PGSTAT_STAT_INTERVAL))
            return;
      last_report = now;

      /*
       * Scan through the TabStatusArray struct(s) to find tables that actually
       * have counts, and build messages to send.  We have to separate shared
       * relations from regular ones because the databaseid field in the message
       * header has to depend on that.
       */
      regular_msg.m_databaseid = MyDatabaseId;
      shared_msg.m_databaseid = InvalidOid;
      regular_msg.m_nentries = 0;
      shared_msg.m_nentries = 0;

      for (tsa = pgStatTabList; tsa != NULL; tsa = tsa->tsa_next)
      {
            for (i = 0; i < tsa->tsa_used; i++)
            {
                  PgStat_TableStatus *entry = &tsa->tsa_entries[i];
                  PgStat_MsgTabstat *this_msg;
                  PgStat_TableEntry *this_ent;

                  /* Shouldn't have any pending transaction-dependent counts */
                  Assert(entry->trans == NULL);

                  /*
                   * Ignore entries that didn't accumulate any actual counts, such
                   * as indexes that were opened by the planner but not used.
                   */
                  if (memcmp(&entry->t_counts, &all_zeroes,
                                 sizeof(PgStat_TableCounts)) == 0)
                        continue;

                  /*
                   * OK, insert data into the appropriate message, and send if full.
                   */
                  this_msg = entry->t_shared ? &shared_msg : &regular_msg;
                  this_ent = &this_msg->m_entry[this_msg->m_nentries];
                  this_ent->t_id = entry->t_id;
                  memcpy(&this_ent->t_counts, &entry->t_counts,
                           sizeof(PgStat_TableCounts));
                  if (++this_msg->m_nentries >= PGSTAT_NUM_TABENTRIES)
                  {
                        pgstat_send_tabstat(this_msg);
                        this_msg->m_nentries = 0;
                  }
            }
            /* zero out TableStatus structs after use */
            MemSet(tsa->tsa_entries, 0,
                     tsa->tsa_used * sizeof(PgStat_TableStatus));
            tsa->tsa_used = 0;
      }

      /*
       * Send partial messages.  If force is true, make sure that any pending
       * xact commit/abort gets counted, even if no table stats to send.
       */
      if (regular_msg.m_nentries > 0 ||
            (force && (pgStatXactCommit > 0 || pgStatXactRollback > 0)))
            pgstat_send_tabstat(&regular_msg);
      if (shared_msg.m_nentries > 0)
            pgstat_send_tabstat(&shared_msg);

      /* Now, send function statistics */
      pgstat_send_funcstats();
}

/*
 * Subroutine for pgstat_report_stat: finish and send a tabstat message
 */
static void
pgstat_send_tabstat(PgStat_MsgTabstat *tsmsg)
{
      int               n;
      int               len;

      /* It's unlikely we'd get here with no socket, but maybe not impossible */
      if (pgStatSock < 0)
            return;

      /*
       * Report accumulated xact commit/rollback whenever we send a normal
       * tabstat message
       */
      if (OidIsValid(tsmsg->m_databaseid))
      {
            tsmsg->m_xact_commit = pgStatXactCommit;
            tsmsg->m_xact_rollback = pgStatXactRollback;
            pgStatXactCommit = 0;
            pgStatXactRollback = 0;
      }
      else
      {
            tsmsg->m_xact_commit = 0;
            tsmsg->m_xact_rollback = 0;
      }

      n = tsmsg->m_nentries;
      len = offsetof(PgStat_MsgTabstat, m_entry[0]) +
            n * sizeof(PgStat_TableEntry);

      pgstat_setheader(&tsmsg->m_hdr, PGSTAT_MTYPE_TABSTAT);
      pgstat_send(tsmsg, len);
}

/*
 * Subroutine for pgstat_report_stat: populate and send a function stat message
 */
static void
pgstat_send_funcstats(void)
{
      /* we assume this inits to all zeroes: */
      static const PgStat_FunctionCounts all_zeroes;

      PgStat_MsgFuncstat msg;
      PgStat_BackendFunctionEntry *entry;
      HASH_SEQ_STATUS fstat;

      if (pgStatFunctions == NULL)
            return;

      pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_FUNCSTAT);
      msg.m_databaseid = MyDatabaseId;
      msg.m_nentries = 0;

      hash_seq_init(&fstat, pgStatFunctions);
      while ((entry = (PgStat_BackendFunctionEntry *) hash_seq_search(&fstat)) != NULL)
      {
            PgStat_FunctionEntry *m_ent;

            /* Skip it if no counts accumulated since last time */
            if (memcmp(&entry->f_counts, &all_zeroes,
                           sizeof(PgStat_FunctionCounts)) == 0)
                  continue;

            /* need to convert format of time accumulators */
            m_ent = &msg.m_entry[msg.m_nentries];
            m_ent->f_id = entry->f_id;
            m_ent->f_numcalls = entry->f_counts.f_numcalls;
            m_ent->f_time = INSTR_TIME_GET_MICROSEC(entry->f_counts.f_time);
            m_ent->f_time_self = INSTR_TIME_GET_MICROSEC(entry->f_counts.f_time_self);

            if (++msg.m_nentries >= PGSTAT_NUM_FUNCENTRIES)
            {
                  pgstat_send(&msg, offsetof(PgStat_MsgFuncstat, m_entry[0]) +
                                    msg.m_nentries * sizeof(PgStat_FunctionEntry));
                  msg.m_nentries = 0;
            }

            /* reset the entry's counts */
            MemSet(&entry->f_counts, 0, sizeof(PgStat_FunctionCounts));
      }

      if (msg.m_nentries > 0)
            pgstat_send(&msg, offsetof(PgStat_MsgFuncstat, m_entry[0]) +
                              msg.m_nentries * sizeof(PgStat_FunctionEntry));

      have_function_stats = false;
}


/* ----------
 * pgstat_vacuum_stat() -
 *
 *    Will tell the collector about objects he can get rid of.
 * ----------
 */
void
pgstat_vacuum_stat(void)
{
      HTAB     *htab;
      PgStat_MsgTabpurge msg;
      PgStat_MsgFuncpurge f_msg;
      HASH_SEQ_STATUS hstat;
      PgStat_StatDBEntry *dbentry;
      PgStat_StatTabEntry *tabentry;
      PgStat_StatFuncEntry *funcentry;
      int               len;

      if (pgStatSock < 0)
            return;

      /*
       * If not done for this transaction, read the statistics collector stats
       * file into some hash tables.
       */
      backend_read_statsfile();

      /*
       * Read pg_database and make a list of OIDs of all existing databases
       */
      htab = pgstat_collect_oids(DatabaseRelationId);

      /*
       * Search the database hash table for dead databases and tell the
       * collector to drop them.
       */
      hash_seq_init(&hstat, pgStatDBHash);
      while ((dbentry = (PgStat_StatDBEntry *) hash_seq_search(&hstat)) != NULL)
      {
            Oid               dbid = dbentry->databaseid;

            CHECK_FOR_INTERRUPTS();

            /* the DB entry for shared tables (with InvalidOid) is never dropped */
            if (OidIsValid(dbid) &&
                  hash_search(htab, (void *) &dbid, HASH_FIND, NULL) == NULL)
                  pgstat_drop_database(dbid);
      }

      /* Clean up */
      hash_destroy(htab);

      /*
       * Lookup our own database entry; if not found, nothing more to do.
       */
      dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
                                                                         (void *) &MyDatabaseId,
                                                                         HASH_FIND, NULL);
      if (dbentry == NULL || dbentry->tables == NULL)
            return;

      /*
       * Similarly to above, make a list of all known relations in this DB.
       */
      htab = pgstat_collect_oids(RelationRelationId);

      /*
       * Initialize our messages table counter to zero
       */
      msg.m_nentries = 0;

      /*
       * Check for all tables listed in stats hashtable if they still exist.
       */
      hash_seq_init(&hstat, dbentry->tables);
      while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&hstat)) != NULL)
      {
            Oid               tabid = tabentry->tableid;

            CHECK_FOR_INTERRUPTS();

            if (hash_search(htab, (void *) &tabid, HASH_FIND, NULL) != NULL)
                  continue;

            /*
             * Not there, so add this table's Oid to the message
             */
            msg.m_tableid[msg.m_nentries++] = tabid;

            /*
             * If the message is full, send it out and reinitialize to empty
             */
            if (msg.m_nentries >= PGSTAT_NUM_TABPURGE)
            {
                  len = offsetof(PgStat_MsgTabpurge, m_tableid[0])
                        +msg.m_nentries * sizeof(Oid);

                  pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
                  msg.m_databaseid = MyDatabaseId;
                  pgstat_send(&msg, len);

                  msg.m_nentries = 0;
            }
      }

      /*
       * Send the rest
       */
      if (msg.m_nentries > 0)
      {
            len = offsetof(PgStat_MsgTabpurge, m_tableid[0])
                  +msg.m_nentries * sizeof(Oid);

            pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
            msg.m_databaseid = MyDatabaseId;
            pgstat_send(&msg, len);
      }

      /* Clean up */
      hash_destroy(htab);

      /*
       * Now repeat the above steps for functions.  However, we needn't bother
       * in the common case where no function stats are being collected.
       */
      if (dbentry->functions != NULL &&
            hash_get_num_entries(dbentry->functions) > 0)
      {
            htab = pgstat_collect_oids(ProcedureRelationId);

            pgstat_setheader(&f_msg.m_hdr, PGSTAT_MTYPE_FUNCPURGE);
            f_msg.m_databaseid = MyDatabaseId;
            f_msg.m_nentries = 0;

            hash_seq_init(&hstat, dbentry->functions);
            while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&hstat)) != NULL)
            {
                  Oid               funcid = funcentry->functionid;

                  CHECK_FOR_INTERRUPTS();

                  if (hash_search(htab, (void *) &funcid, HASH_FIND, NULL) != NULL)
                        continue;

                  /*
                   * Not there, so add this function's Oid to the message
                   */
                  f_msg.m_functionid[f_msg.m_nentries++] = funcid;

                  /*
                   * If the message is full, send it out and reinitialize to empty
                   */
                  if (f_msg.m_nentries >= PGSTAT_NUM_FUNCPURGE)
                  {
                        len = offsetof(PgStat_MsgFuncpurge, m_functionid[0])
                              +f_msg.m_nentries * sizeof(Oid);

                        pgstat_send(&f_msg, len);

                        f_msg.m_nentries = 0;
                  }
            }

            /*
             * Send the rest
             */
            if (f_msg.m_nentries > 0)
            {
                  len = offsetof(PgStat_MsgFuncpurge, m_functionid[0])
                        +f_msg.m_nentries * sizeof(Oid);

                  pgstat_send(&f_msg, len);
            }

            hash_destroy(htab);
      }
}


/* ----------
 * pgstat_collect_oids() -
 *
 *    Collect the OIDs of all objects listed in the specified system catalog
 *    into a temporary hash table.  Caller should hash_destroy the result
 *    when done with it.
 * ----------
 */
static HTAB *
pgstat_collect_oids(Oid catalogid)
{
      HTAB     *htab;
      HASHCTL           hash_ctl;
      Relation    rel;
      HeapScanDesc scan;
      HeapTuple   tup;

      memset(&hash_ctl, 0, sizeof(hash_ctl));
      hash_ctl.keysize = sizeof(Oid);
      hash_ctl.entrysize = sizeof(Oid);
      hash_ctl.hash = oid_hash;
      htab = hash_create("Temporary table of OIDs",
                                 PGSTAT_TAB_HASH_SIZE,
                                 &hash_ctl,
                                 HASH_ELEM | HASH_FUNCTION);

      rel = heap_open(catalogid, AccessShareLock);
      scan = heap_beginscan(rel, SnapshotNow, 0, NULL);
      while ((tup = heap_getnext(scan, ForwardScanDirection)) != NULL)
      {
            Oid               thisoid = HeapTupleGetOid(tup);

            CHECK_FOR_INTERRUPTS();

            (void) hash_search(htab, (void *) &thisoid, HASH_ENTER, NULL);
      }
      heap_endscan(scan);
      heap_close(rel, AccessShareLock);

      return htab;
}


/* ----------
 * pgstat_drop_database() -
 *
 *    Tell the collector that we just dropped a database.
 *    (If the message gets lost, we will still clean the dead DB eventually
 *    via future invocations of pgstat_vacuum_stat().)
 * ----------
 */
void
pgstat_drop_database(Oid databaseid)
{
      PgStat_MsgDropdb msg;

      if (pgStatSock < 0)
            return;

      pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_DROPDB);
      msg.m_databaseid = databaseid;
      pgstat_send(&msg, sizeof(msg));
}


/* ----------
 * pgstat_drop_relation() -
 *
 *    Tell the collector that we just dropped a relation.
 *    (If the message gets lost, we will still clean the dead entry eventually
 *    via future invocations of pgstat_vacuum_stat().)
 *
 *    Currently not used for lack of any good place to call it; we rely
 *    entirely on pgstat_vacuum_stat() to clean out stats for dead rels.
 * ----------
 */
#ifdef NOT_USED
void
pgstat_drop_relation(Oid relid)
{
      PgStat_MsgTabpurge msg;
      int               len;

      if (pgStatSock < 0)
            return;

      msg.m_tableid[0] = relid;
      msg.m_nentries = 1;

      len = offsetof(PgStat_MsgTabpurge, m_tableid[0]) +sizeof(Oid);

      pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
      msg.m_databaseid = MyDatabaseId;
      pgstat_send(&msg, len);
}
#endif   /* NOT_USED */


/* ----------
 * pgstat_reset_counters() -
 *
 *    Tell the statistics collector to reset counters for our database.
 * ----------
 */
void
pgstat_reset_counters(void)
{
      PgStat_MsgResetcounter msg;

      if (pgStatSock < 0)
            return;

      if (!superuser())
            ereport(ERROR,
                        (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                         errmsg("must be superuser to reset statistics counters")));

      pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETCOUNTER);
      msg.m_databaseid = MyDatabaseId;
      pgstat_send(&msg, sizeof(msg));
}


/* ----------
 * pgstat_report_autovac() -
 *
 *    Called from autovacuum.c to report startup of an autovacuum process.
 *    We are called before InitPostgres is done, so can't rely on MyDatabaseId;
 *    the db OID must be passed in, instead.
 * ----------
 */
void
pgstat_report_autovac(Oid dboid)
{
      PgStat_MsgAutovacStart msg;

      if (pgStatSock < 0)
            return;

      pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_AUTOVAC_START);
      msg.m_databaseid = dboid;
      msg.m_start_time = GetCurrentTimestamp();

      pgstat_send(&msg, sizeof(msg));
}


/* ---------
 * pgstat_report_vacuum() -
 *
 *    Tell the collector about the table we just vacuumed.
 * ---------
 */
void
pgstat_report_vacuum(Oid tableoid, bool shared, bool scanned_all,
                               bool analyze, PgStat_Counter tuples)
{
      PgStat_MsgVacuum msg;

      if (pgStatSock < 0 || !pgstat_track_counts)
            return;

      pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_VACUUM);
      msg.m_databaseid = shared ? InvalidOid : MyDatabaseId;
      msg.m_tableoid = tableoid;
      msg.m_scanned_all = scanned_all;
      msg.m_analyze = analyze;
      msg.m_autovacuum = IsAutoVacuumWorkerProcess();       /* is this autovacuum? */
      msg.m_vacuumtime = GetCurrentTimestamp();
      msg.m_tuples = tuples;
      pgstat_send(&msg, sizeof(msg));
}

/* --------
 * pgstat_report_analyze() -
 *
 *    Tell the collector about the table we just analyzed.
 * --------
 */
void
pgstat_report_analyze(Relation rel, PgStat_Counter livetuples,
                                PgStat_Counter deadtuples)
{
      PgStat_MsgAnalyze msg;

      if (pgStatSock < 0 || !pgstat_track_counts)
            return;

      /*
       * Unlike VACUUM, ANALYZE might be running inside a transaction that has
       * already inserted and/or deleted rows in the target table. ANALYZE will
       * have counted such rows as live or dead respectively. Because we will
       * report our counts of such rows at transaction end, we should subtract
       * off these counts from what we send to the collector now, else they'll
       * be double-counted after commit.  (This approach also ensures that the
       * collector ends up with the right numbers if we abort instead of
       * committing.)
       */
      if (rel->pgstat_info != NULL)
      {
            PgStat_TableXactStatus *trans;

            for (trans = rel->pgstat_info->trans; trans; trans = trans->upper)
            {
                  livetuples -= trans->tuples_inserted - trans->tuples_deleted;
                  deadtuples -= trans->tuples_deleted;
            }
            /* count stuff inserted by already-aborted subxacts, too */
            deadtuples -= rel->pgstat_info->t_counts.t_new_dead_tuples;
            /* Since ANALYZE's counts are estimates, we could have underflowed */
            livetuples = Max(livetuples, 0);
            deadtuples = Max(deadtuples, 0);
      }

      pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_ANALYZE);
      msg.m_databaseid = rel->rd_rel->relisshared ? InvalidOid : MyDatabaseId;
      msg.m_tableoid = RelationGetRelid(rel);
      msg.m_autovacuum = IsAutoVacuumWorkerProcess();       /* is this autovacuum? */
      msg.m_analyzetime = GetCurrentTimestamp();
      msg.m_live_tuples = livetuples;
      msg.m_dead_tuples = deadtuples;
      pgstat_send(&msg, sizeof(msg));
}


/* ----------
 * pgstat_ping() -
 *
 *    Send some junk data to the collector to increase traffic.
 * ----------
 */
void
pgstat_ping(void)
{
      PgStat_MsgDummy msg;

      if (pgStatSock < 0)
            return;

      pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_DUMMY);
      pgstat_send(&msg, sizeof(msg));
}

/* ----------
 * pgstat_send_inquiry() -
 *
 *    Notify collector that we need fresh data.
 *    ts specifies the minimum acceptable timestamp for the stats file.
 * ----------
 */
static void
pgstat_send_inquiry(TimestampTz ts)
{
      PgStat_MsgInquiry msg;

      pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_INQUIRY);
      msg.inquiry_time = ts;
      pgstat_send(&msg, sizeof(msg));
}


/*
 * Initialize function call usage data.
 * Called by the executor before invoking a function.
 */
void
pgstat_init_function_usage(FunctionCallInfoData *fcinfo,
                                       PgStat_FunctionCallUsage *fcu)
{
      PgStat_BackendFunctionEntry *htabent;
      bool        found;

      if (pgstat_track_functions <= fcinfo->flinfo->fn_stats)
      {
            /* stats not wanted */
            fcu->fs = NULL;
            return;
      }

      if (!pgStatFunctions)
      {
            /* First time through - initialize function stat table */
            HASHCTL           hash_ctl;

            memset(&hash_ctl, 0, sizeof(hash_ctl));
            hash_ctl.keysize = sizeof(Oid);
            hash_ctl.entrysize = sizeof(PgStat_BackendFunctionEntry);
            hash_ctl.hash = oid_hash;
            pgStatFunctions = hash_create("Function stat entries",
                                                        PGSTAT_FUNCTION_HASH_SIZE,
                                                        &hash_ctl,
                                                        HASH_ELEM | HASH_FUNCTION);
      }

      /* Get the stats entry for this function, create if necessary */
      htabent = hash_search(pgStatFunctions, &fcinfo->flinfo->fn_oid,
                                      HASH_ENTER, &found);
      if (!found)
            MemSet(&htabent->f_counts, 0, sizeof(PgStat_FunctionCounts));

      fcu->fs = &htabent->f_counts;

      /* save stats for this function, later used to compensate for recursion */
      fcu->save_f_time = htabent->f_counts.f_time;

      /* save current backend-wide total time */
      fcu->save_total = total_func_time;

      /* get clock time as of function start */
      INSTR_TIME_SET_CURRENT(fcu->f_start);
}

/*
 * Calculate function call usage and update stat counters.
 * Called by the executor after invoking a function.
 *
 * In the case of a set-returning function that runs in value-per-call mode,
 * we will see multiple pgstat_init_function_usage/pgstat_end_function_usage
 * calls for what the user considers a single call of the function.  The
 * finalize flag should be TRUE on the last call.
 */
void
pgstat_end_function_usage(PgStat_FunctionCallUsage *fcu, bool finalize)
{
      PgStat_FunctionCounts *fs = fcu->fs;
      instr_time  f_total;
      instr_time  f_others;
      instr_time  f_self;

      /* stats not wanted? */
      if (fs == NULL)
            return;

      /* total elapsed time in this function call */
      INSTR_TIME_SET_CURRENT(f_total);
      INSTR_TIME_SUBTRACT(f_total, fcu->f_start);

      /* self usage: elapsed minus anything already charged to other calls */
      f_others = total_func_time;
      INSTR_TIME_SUBTRACT(f_others, fcu->save_total);
      f_self = f_total;
      INSTR_TIME_SUBTRACT(f_self, f_others);

      /* update backend-wide total time */
      INSTR_TIME_ADD(total_func_time, f_self);

      /*
       * Compute the new total f_time as the total elapsed time added to the
       * pre-call value of f_time.  This is necessary to avoid double-counting
       * any time taken by recursive calls of myself.  (We do not need any
       * similar kluge for self time, since that already excludes any recursive
       * calls.)
       */
      INSTR_TIME_ADD(f_total, fcu->save_f_time);

      /* update counters in function stats table */
      if (finalize)
            fs->f_numcalls++;
      fs->f_time = f_total;
      INSTR_TIME_ADD(fs->f_time_self, f_self);

      /* indicate that we have something to send */
      have_function_stats = true;
}


/* ----------
 * pgstat_initstats() -
 *
 *    Initialize a relcache entry to count access statistics.
 *    Called whenever a relation is opened.
 *
 *    We assume that a relcache entry's pgstat_info field is zeroed by
 *    relcache.c when the relcache entry is made; thereafter it is long-lived
 *    data.  We can avoid repeated searches of the TabStatus arrays when the
 *    same relation is touched repeatedly within a transaction.
 * ----------
 */
void
pgstat_initstats(Relation rel)
{
      Oid               rel_id = rel->rd_id;
      char        relkind = rel->rd_rel->relkind;

      /* We only count stats for things that have storage */
      if (!(relkind == RELKIND_RELATION ||
              relkind == RELKIND_INDEX ||
              relkind == RELKIND_TOASTVALUE))
      {
            rel->pgstat_info = NULL;
            return;
      }

      if (pgStatSock < 0 || !pgstat_track_counts)
      {
            /* We're not counting at all */
            rel->pgstat_info = NULL;
            return;
      }

      /*
       * If we already set up this relation in the current transaction, nothing
       * to do.
       */
      if (rel->pgstat_info != NULL &&
            rel->pgstat_info->t_id == rel_id)
            return;

      /* Else find or make the PgStat_TableStatus entry, and update link */
      rel->pgstat_info = get_tabstat_entry(rel_id, rel->rd_rel->relisshared);
}

/*
 * get_tabstat_entry - find or create a PgStat_TableStatus entry for rel
 */
static PgStat_TableStatus *
get_tabstat_entry(Oid rel_id, bool isshared)
{
      PgStat_TableStatus *entry;
      TabStatusArray *tsa;
      TabStatusArray *prev_tsa;
      int               i;

      /*
       * Search the already-used tabstat slots for this relation.
       */
      prev_tsa = NULL;
      for (tsa = pgStatTabList; tsa != NULL; prev_tsa = tsa, tsa = tsa->tsa_next)
      {
            for (i = 0; i < tsa->tsa_used; i++)
            {
                  entry = &tsa->tsa_entries[i];
                  if (entry->t_id == rel_id)
                        return entry;
            }

            if (tsa->tsa_used < TABSTAT_QUANTUM)
            {
                  /*
                   * It must not be present, but we found a free slot instead. Fine,
                   * let's use this one.  We assume the entry was already zeroed,
                   * either at creation or after last use.
                   */
                  entry = &tsa->tsa_entries[tsa->tsa_used++];
                  entry->t_id = rel_id;
                  entry->t_shared = isshared;
                  return entry;
            }
      }

      /*
       * We ran out of tabstat slots, so allocate more.  Be sure they're zeroed.
       */
      tsa = (TabStatusArray *) MemoryContextAllocZero(TopMemoryContext,
                                                                              sizeof(TabStatusArray));
      if (prev_tsa)
            prev_tsa->tsa_next = tsa;
      else
            pgStatTabList = tsa;

      /*
       * Use the first entry of the new TabStatusArray.
       */
      entry = &tsa->tsa_entries[tsa->tsa_used++];
      entry->t_id = rel_id;
      entry->t_shared = isshared;
      return entry;
}

/*
 * get_tabstat_stack_level - add a new (sub)transaction stack entry if needed
 */
static PgStat_SubXactStatus *
get_tabstat_stack_level(int nest_level)
{
      PgStat_SubXactStatus *xact_state;

      xact_state = pgStatXactStack;
      if (xact_state == NULL || xact_state->nest_level != nest_level)
      {
            xact_state = (PgStat_SubXactStatus *)
                  MemoryContextAlloc(TopTransactionContext,
                                             sizeof(PgStat_SubXactStatus));
            xact_state->nest_level = nest_level;
            xact_state->prev = pgStatXactStack;
            xact_state->first = NULL;
            pgStatXactStack = xact_state;
      }
      return xact_state;
}

/*
 * add_tabstat_xact_level - add a new (sub)transaction state record
 */
static void
add_tabstat_xact_level(PgStat_TableStatus *pgstat_info, int nest_level)
{
      PgStat_SubXactStatus *xact_state;
      PgStat_TableXactStatus *trans;

      /*
       * If this is the first rel to be modified at the current nest level, we
       * first have to push a transaction stack entry.
       */
      xact_state = get_tabstat_stack_level(nest_level);

      /* Now make a per-table stack entry */
      trans = (PgStat_TableXactStatus *)
            MemoryContextAllocZero(TopTransactionContext,
                                             sizeof(PgStat_TableXactStatus));
      trans->nest_level = nest_level;
      trans->upper = pgstat_info->trans;
      trans->parent = pgstat_info;
      trans->next = xact_state->first;
      xact_state->first = trans;
      pgstat_info->trans = trans;
}

/*
 * pgstat_count_heap_insert - count a tuple insertion
 */
void
pgstat_count_heap_insert(Relation rel)
{
      PgStat_TableStatus *pgstat_info = rel->pgstat_info;

      if (pgstat_track_counts && pgstat_info != NULL)
      {
            int               nest_level = GetCurrentTransactionNestLevel();

            /* t_tuples_inserted is nontransactional, so just advance it */
            pgstat_info->t_counts.t_tuples_inserted++;

            /* We have to log the transactional effect at the proper level */
            if (pgstat_info->trans == NULL ||
                  pgstat_info->trans->nest_level != nest_level)
                  add_tabstat_xact_level(pgstat_info, nest_level);

            pgstat_info->trans->tuples_inserted++;
      }
}

/*
 * pgstat_count_heap_update - count a tuple update
 */
void
pgstat_count_heap_update(Relation rel, bool hot)
{
      PgStat_TableStatus *pgstat_info = rel->pgstat_info;

      if (pgstat_track_counts && pgstat_info != NULL)
      {
            int               nest_level = GetCurrentTransactionNestLevel();

            /* t_tuples_updated is nontransactional, so just advance it */
            pgstat_info->t_counts.t_tuples_updated++;
            /* ditto for the hot_update counter */
            if (hot)
                  pgstat_info->t_counts.t_tuples_hot_updated++;

            /* We have to log the transactional effect at the proper level */
            if (pgstat_info->trans == NULL ||
                  pgstat_info->trans->nest_level != nest_level)
                  add_tabstat_xact_level(pgstat_info, nest_level);

            /* An UPDATE both inserts a new tuple and deletes the old */
            pgstat_info->trans->tuples_inserted++;
            pgstat_info->trans->tuples_deleted++;
      }
}

/*
 * pgstat_count_heap_delete - count a tuple deletion
 */
void
pgstat_count_heap_delete(Relation rel)
{
      PgStat_TableStatus *pgstat_info = rel->pgstat_info;

      if (pgstat_track_counts && pgstat_info != NULL)
      {
            int               nest_level = GetCurrentTransactionNestLevel();

            /* t_tuples_deleted is nontransactional, so just advance it */
            pgstat_info->t_counts.t_tuples_deleted++;

            /* We have to log the transactional effect at the proper level */
            if (pgstat_info->trans == NULL ||
                  pgstat_info->trans->nest_level != nest_level)
                  add_tabstat_xact_level(pgstat_info, nest_level);

            pgstat_info->trans->tuples_deleted++;
      }
}

/*
 * pgstat_update_heap_dead_tuples - update dead-tuples count
 *
 * The semantics of this are that we are reporting the nontransactional
 * recovery of "delta" dead tuples; so t_new_dead_tuples decreases
 * rather than increasing, and the change goes straight into the per-table
 * counter, not into transactional state.
 */
void
pgstat_update_heap_dead_tuples(Relation rel, int delta)
{
      PgStat_TableStatus *pgstat_info = rel->pgstat_info;

      if (pgstat_track_counts && pgstat_info != NULL)
            pgstat_info->t_counts.t_new_dead_tuples -= delta;
}


/* ----------
 * AtEOXact_PgStat
 *
 *    Called from access/transam/xact.c at top-level transaction commit/abort.
 * ----------
 */
void
AtEOXact_PgStat(bool isCommit)
{
      PgStat_SubXactStatus *xact_state;

      /*
       * Count transaction commit or abort.  (We use counters, not just bools,
       * in case the reporting message isn't sent right away.)
       */
      if (isCommit)
            pgStatXactCommit++;
      else
            pgStatXactRollback++;

      /*
       * Transfer transactional insert/update counts into the base tabstat
       * entries.  We don't bother to free any of the transactional state, since
       * it's all in TopTransactionContext and will go away anyway.
       */
      xact_state = pgStatXactStack;
      if (xact_state != NULL)
      {
            PgStat_TableXactStatus *trans;

            Assert(xact_state->nest_level == 1);
            Assert(xact_state->prev == NULL);
            for (trans = xact_state->first; trans != NULL; trans = trans->next)
            {
                  PgStat_TableStatus *tabstat;

                  Assert(trans->nest_level == 1);
                  Assert(trans->upper == NULL);
                  tabstat = trans->parent;
                  Assert(tabstat->trans == trans);
                  if (isCommit)
                  {
                        tabstat->t_counts.t_new_live_tuples +=
                              trans->tuples_inserted - trans->tuples_deleted;
                        tabstat->t_counts.t_new_dead_tuples += trans->tuples_deleted;
                  }
                  else
                  {
                        /* inserted tuples are dead, deleted tuples are unaffected */
                        tabstat->t_counts.t_new_dead_tuples += trans->tuples_inserted;
                  }
                  tabstat->trans = NULL;
            }
      }
      pgStatXactStack = NULL;

      /* Make sure any stats snapshot is thrown away */
      pgstat_clear_snapshot();
}

/* ----------
 * AtEOSubXact_PgStat
 *
 *    Called from access/transam/xact.c at subtransaction commit/abort.
 * ----------
 */
void
AtEOSubXact_PgStat(bool isCommit, int nestDepth)
{
      PgStat_SubXactStatus *xact_state;

      /*
       * Transfer transactional insert/update counts into the next higher
       * subtransaction state.
       */
      xact_state = pgStatXactStack;
      if (xact_state != NULL &&
            xact_state->nest_level >= nestDepth)
      {
            PgStat_TableXactStatus *trans;
            PgStat_TableXactStatus *next_trans;

            /* delink xact_state from stack immediately to simplify reuse case */
            pgStatXactStack = xact_state->prev;

            for (trans = xact_state->first; trans != NULL; trans = next_trans)
            {
                  PgStat_TableStatus *tabstat;

                  next_trans = trans->next;
                  Assert(trans->nest_level == nestDepth);
                  tabstat = trans->parent;
                  Assert(tabstat->trans == trans);
                  if (isCommit)
                  {
                        if (trans->upper && trans->upper->nest_level == nestDepth - 1)
                        {
                              trans->upper->tuples_inserted += trans->tuples_inserted;
                              trans->upper->tuples_deleted += trans->tuples_deleted;
                              tabstat->trans = trans->upper;
                              pfree(trans);
                        }
                        else
                        {
                              /*
                               * When there isn't an immediate parent state, we can just
                               * reuse the record instead of going through a
                               * palloc/pfree pushup (this works since it's all in
                               * TopTransactionContext anyway).  We have to re-link it
                               * into the parent level, though, and that might mean
                               * pushing a new entry into the pgStatXactStack.
                               */
                              PgStat_SubXactStatus *upper_xact_state;

                              upper_xact_state = get_tabstat_stack_level(nestDepth - 1);
                              trans->next = upper_xact_state->first;
                              upper_xact_state->first = trans;
                              trans->nest_level = nestDepth - 1;
                        }
                  }
                  else
                  {
                        /*
                         * On abort, inserted tuples are dead (and can be bounced out
                         * to the top-level tabstat), deleted tuples are unaffected
                         */
                        tabstat->t_counts.t_new_dead_tuples += trans->tuples_inserted;
                        tabstat->trans = trans->upper;
                        pfree(trans);
                  }
            }
            pfree(xact_state);
      }
}


/*
 * AtPrepare_PgStat
 *          Save the transactional stats state at 2PC transaction prepare.
 *
 * In this phase we just generate 2PC records for all the pending
 * transaction-dependent stats work.
 */
void
AtPrepare_PgStat(void)
{
      PgStat_SubXactStatus *xact_state;

      xact_state = pgStatXactStack;
      if (xact_state != NULL)
      {
            PgStat_TableXactStatus *trans;

            Assert(xact_state->nest_level == 1);
            Assert(xact_state->prev == NULL);
            for (trans = xact_state->first; trans != NULL; trans = trans->next)
            {
                  PgStat_TableStatus *tabstat;
                  TwoPhasePgStatRecord record;

                  Assert(trans->nest_level == 1);
                  Assert(trans->upper == NULL);
                  tabstat = trans->parent;
                  Assert(tabstat->trans == trans);

                  record.tuples_inserted = trans->tuples_inserted;
                  record.tuples_deleted = trans->tuples_deleted;
                  record.t_id = tabstat->t_id;
                  record.t_shared = tabstat->t_shared;

                  RegisterTwoPhaseRecord(TWOPHASE_RM_PGSTAT_ID, 0,
                                                   &record, sizeof(TwoPhasePgStatRecord));
            }
      }
}

/*
 * PostPrepare_PgStat
 *          Clean up after successful PREPARE.
 *
 * All we need do here is unlink the transaction stats state from the
 * nontransactional state.    The nontransactional action counts will be
 * reported to the stats collector immediately, while the effects on live
 * and dead tuple counts are preserved in the 2PC state file.
 *
 * Note: AtEOXact_PgStat is not called during PREPARE.
 */
void
PostPrepare_PgStat(void)
{
      PgStat_SubXactStatus *xact_state;

      /*
       * We don't bother to free any of the transactional state, since it's all
       * in TopTransactionContext and will go away anyway.
       */
      xact_state = pgStatXactStack;
      if (xact_state != NULL)
      {
            PgStat_TableXactStatus *trans;

            for (trans = xact_state->first; trans != NULL; trans = trans->next)
            {
                  PgStat_TableStatus *tabstat;

                  tabstat = trans->parent;
                  tabstat->trans = NULL;
            }
      }
      pgStatXactStack = NULL;

      /* Make sure any stats snapshot is thrown away */
      pgstat_clear_snapshot();
}

/*
 * 2PC processing routine for COMMIT PREPARED case.
 *
 * Load the saved counts into our local pgstats state.
 */
void
pgstat_twophase_postcommit(TransactionId xid, uint16 info,
                                       void *recdata, uint32 len)
{
      TwoPhasePgStatRecord *rec = (TwoPhasePgStatRecord *) recdata;
      PgStat_TableStatus *pgstat_info;

      /* Find or create a tabstat entry for the rel */
      pgstat_info = get_tabstat_entry(rec->t_id, rec->t_shared);

      pgstat_info->t_counts.t_new_live_tuples +=
            rec->tuples_inserted - rec->tuples_deleted;
      pgstat_info->t_counts.t_new_dead_tuples += rec->tuples_deleted;
}

/*
 * 2PC processing routine for ROLLBACK PREPARED case.
 *
 * Load the saved counts into our local pgstats state, but treat them
 * as aborted.
 */
void
pgstat_twophase_postabort(TransactionId xid, uint16 info,
                                      void *recdata, uint32 len)
{
      TwoPhasePgStatRecord *rec = (TwoPhasePgStatRecord *) recdata;
      PgStat_TableStatus *pgstat_info;

      /* Find or create a tabstat entry for the rel */
      pgstat_info = get_tabstat_entry(rec->t_id, rec->t_shared);

      /* inserted tuples are dead, deleted tuples are no-ops */
      pgstat_info->t_counts.t_new_dead_tuples += rec->tuples_inserted;
}


/* ----------
 * pgstat_fetch_stat_dbentry() -
 *
 *    Support function for the SQL-callable pgstat* functions. Returns
 *    the collected statistics for one database or NULL. NULL doesn't mean
 *    that the database doesn't exist, it is just not yet known by the
 *    collector, so the caller is better off to report ZERO instead.
 * ----------
 */
PgStat_StatDBEntry *
pgstat_fetch_stat_dbentry(Oid dbid)
{
      /*
       * If not done for this transaction, read the statistics collector stats
       * file into some hash tables.
       */
      backend_read_statsfile();

      /*
       * Lookup the requested database; return NULL if not found
       */
      return (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
                                                                    (void *) &dbid,
                                                                    HASH_FIND, NULL);
}


/* ----------
 * pgstat_fetch_stat_tabentry() -
 *
 *    Support function for the SQL-callable pgstat* functions. Returns
 *    the collected statistics for one table or NULL. NULL doesn't mean
 *    that the table doesn't exist, it is just not yet known by the
 *    collector, so the caller is better off to report ZERO instead.
 * ----------
 */
PgStat_StatTabEntry *
pgstat_fetch_stat_tabentry(Oid relid)
{
      Oid               dbid;
      PgStat_StatDBEntry *dbentry;
      PgStat_StatTabEntry *tabentry;

      /*
       * If not done for this transaction, read the statistics collector stats
       * file into some hash tables.
       */
      backend_read_statsfile();

      /*
       * Lookup our database, then look in its table hash table.
       */
      dbid = MyDatabaseId;
      dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
                                                                         (void *) &dbid,
                                                                         HASH_FIND, NULL);
      if (dbentry != NULL && dbentry->tables != NULL)
      {
            tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
                                                                                 (void *) &relid,
                                                                                 HASH_FIND, NULL);
            if (tabentry)
                  return tabentry;
      }

      /*
       * If we didn't find it, maybe it's a shared table.
       */
      dbid = InvalidOid;
      dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
                                                                         (void *) &dbid,
                                                                         HASH_FIND, NULL);
      if (dbentry != NULL && dbentry->tables != NULL)
      {
            tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
                                                                                 (void *) &relid,
                                                                                 HASH_FIND, NULL);
            if (tabentry)
                  return tabentry;
      }

      return NULL;
}


/* ----------
 * pgstat_fetch_stat_funcentry() -
 *
 *    Support function for the SQL-callable pgstat* functions. Returns
 *    the collected statistics for one function or NULL.
 * ----------
 */
PgStat_StatFuncEntry *
pgstat_fetch_stat_funcentry(Oid func_id)
{
      PgStat_StatDBEntry *dbentry;
      PgStat_StatFuncEntry *funcentry = NULL;

      /* load the stats file if needed */
      backend_read_statsfile();

      /* Lookup our database, then find the requested function.  */
      dbentry = pgstat_fetch_stat_dbentry(MyDatabaseId);
      if (dbentry != NULL && dbentry->functions != NULL)
      {
            funcentry = (PgStat_StatFuncEntry *) hash_search(dbentry->functions,
                                                                                     (void *) &func_id,
                                                                                     HASH_FIND, NULL);
      }

      return funcentry;
}


/* ----------
 * pgstat_fetch_stat_beentry() -
 *
 *    Support function for the SQL-callable pgstat* functions. Returns
 *    our local copy of the current-activity entry for one backend.
 *
 *    NB: caller is responsible for a check if the user is permitted to see
 *    this info (especially the querystring).
 * ----------
 */
PgBackendStatus *
pgstat_fetch_stat_beentry(int beid)
{
      pgstat_read_current_status();

      if (beid < 1 || beid > localNumBackends)
            return NULL;

      return &localBackendStatusTable[beid - 1];
}


/* ----------
 * pgstat_fetch_stat_numbackends() -
 *
 *    Support function for the SQL-callable pgstat* functions. Returns
 *    the maximum current backend id.
 * ----------
 */
int
pgstat_fetch_stat_numbackends(void)
{
      pgstat_read_current_status();

      return localNumBackends;
}

/*
 * ---------
 * pgstat_fetch_global() -
 *
 *    Support function for the SQL-callable pgstat* functions. Returns
 *    a pointer to the global statistics struct.
 * ---------
 */
PgStat_GlobalStats *
pgstat_fetch_global(void)
{
      backend_read_statsfile();

      return &globalStats;
}


/* ------------------------------------------------------------
 * Functions for management of the shared-memory PgBackendStatus array
 * ------------------------------------------------------------
 */

static PgBackendStatus *BackendStatusArray = NULL;
static PgBackendStatus *MyBEEntry = NULL;
static char *BackendActivityBuffer = NULL;


/*
 * Report shared-memory space needed by CreateSharedBackendStatus.
 */
Size
BackendStatusShmemSize(void)
{
      Size        size;

      size = add_size(mul_size(sizeof(PgBackendStatus), MaxBackends),
                              mul_size(pgstat_track_activity_query_size, MaxBackends));
      return size;
}

/*
 * Initialize the shared status array and activity string buffer during
 * postmaster startup.
 */
void
CreateSharedBackendStatus(void)
{
      Size        size;
      bool        found;
      int               i;
      char     *buffer;

      /* Create or attach to the shared array */
      size = mul_size(sizeof(PgBackendStatus), MaxBackends);
      BackendStatusArray = (PgBackendStatus *)
            ShmemInitStruct("Backend Status Array", size, &found);

      if (!found)
      {
            /*
             * We're the first - initialize.
             */
            MemSet(BackendStatusArray, 0, size);
      }

      /* Create or attach to the shared activity buffer */
      size = mul_size(pgstat_track_activity_query_size, MaxBackends);
      BackendActivityBuffer = (char *)
            ShmemInitStruct("Backend Activity Buffer", size, &found);

      if (!found)
      {
            MemSet(BackendActivityBuffer, 0, size);

            /* Initialize st_activity pointers. */
            buffer = BackendActivityBuffer;
            for (i = 0; i < MaxBackends; i++)
            {
                  BackendStatusArray[i].st_activity = buffer;
                  buffer += pgstat_track_activity_query_size;
            }
      }
}


/* ----------
 * pgstat_initialize() -
 *
 *    Initialize pgstats state, and set up our on-proc-exit hook.
 *    Called from InitPostgres.  MyBackendId must be set,
 *    but we must not have started any transaction yet (since the
 *    exit hook must run after the last transaction exit).
 * ----------
 */
void
pgstat_initialize(void)
{
      /* Initialize MyBEEntry */
      Assert(MyBackendId >= 1 && MyBackendId <= MaxBackends);
      MyBEEntry = &BackendStatusArray[MyBackendId - 1];

      /* Set up a process-exit hook to clean up */
      on_shmem_exit(pgstat_beshutdown_hook, 0);
}

/* ----------
 * pgstat_bestart() -
 *
 *    Initialize this backend's entry in the PgBackendStatus array.
 *    Called from InitPostgres.  MyDatabaseId and session userid must be set
 *    (hence, this cannot be combined with pgstat_initialize).
 * ----------
 */
void
pgstat_bestart(void)
{
      TimestampTz proc_start_timestamp;
      Oid               userid;
      SockAddr    clientaddr;
      volatile PgBackendStatus *beentry;

      /*
       * To minimize the time spent modifying the PgBackendStatus entry, fetch
       * all the needed data first.
       *
       * If we have a MyProcPort, use its session start time (for consistency,
       * and to save a kernel call).
       */
      if (MyProcPort)
            proc_start_timestamp = MyProcPort->SessionStartTime;
      else
            proc_start_timestamp = GetCurrentTimestamp();
      userid = GetSessionUserId();

      /*
       * We may not have a MyProcPort (eg, if this is the autovacuum process).
       * If so, use all-zeroes client address, which is dealt with specially in
       * pg_stat_get_backend_client_addr and pg_stat_get_backend_client_port.
       */
      if (MyProcPort)
            memcpy(&clientaddr, &MyProcPort->raddr, sizeof(clientaddr));
      else
            MemSet(&clientaddr, 0, sizeof(clientaddr));

      /*
       * Initialize my status entry, following the protocol of bumping
       * st_changecount before and after; and make sure it's even afterwards. We
       * use a volatile pointer here to ensure the compiler doesn't try to get
       * cute.
       */
      beentry = MyBEEntry;
      do
      {
            beentry->st_changecount++;
      } while ((beentry->st_changecount & 1) == 0);

      beentry->st_procpid = MyProcPid;
      beentry->st_proc_start_timestamp = proc_start_timestamp;
      beentry->st_activity_start_timestamp = 0;
      beentry->st_xact_start_timestamp = 0;
      beentry->st_databaseid = MyDatabaseId;
      beentry->st_userid = userid;
      beentry->st_clientaddr = clientaddr;
      beentry->st_waiting = false;
      beentry->st_activity[0] = '\0';
      /* Also make sure the last byte in the string area is always 0 */
      beentry->st_activity[pgstat_track_activity_query_size - 1] = '\0';

      beentry->st_changecount++;
      Assert((beentry->st_changecount & 1) == 0);
}

/*
 * Shut down a single backend's statistics reporting at process exit.
 *
 * Flush any remaining statistics counts out to the collector.
 * Without this, operations triggered during backend exit (such as
 * temp table deletions) won't be counted.
 *
 * Lastly, clear out our entry in the PgBackendStatus array.
 */
static void
pgstat_beshutdown_hook(int code, Datum arg)
{
      volatile PgBackendStatus *beentry = MyBEEntry;

      pgstat_report_stat(true);

      /*
       * Clear my status entry, following the protocol of bumping st_changecount
       * before and after.  We use a volatile pointer here to ensure the
       * compiler doesn't try to get cute.
       */
      beentry->st_changecount++;

      beentry->st_procpid = 0;      /* mark invalid */

      beentry->st_changecount++;
      Assert((beentry->st_changecount & 1) == 0);
}


/* ----------
 * pgstat_report_activity() -
 *
 *    Called from tcop/postgres.c to report what the backend is actually doing
 *    (usually "<IDLE>" or the start of the query to be executed).
 * ----------
 */
void
pgstat_report_activity(const char *cmd_str)
{
      volatile PgBackendStatus *beentry = MyBEEntry;
      TimestampTz start_timestamp;
      int               len;

      TRACE_POSTGRESQL_STATEMENT_STATUS(cmd_str);

      if (!pgstat_track_activities || !beentry)
            return;

      /*
       * To minimize the time spent modifying the entry, fetch all the needed
       * data first.
       */
      start_timestamp = GetCurrentStatementStartTimestamp();

      len = strlen(cmd_str);
      len = pg_mbcliplen(cmd_str, len, pgstat_track_activity_query_size - 1);

      /*
       * Update my status entry, following the protocol of bumping
       * st_changecount before and after.  We use a volatile pointer here to
       * ensure the compiler doesn't try to get cute.
       */
      beentry->st_changecount++;

      beentry->st_activity_start_timestamp = start_timestamp;
      memcpy((char *) beentry->st_activity, cmd_str, len);
      beentry->st_activity[len] = '\0';

      beentry->st_changecount++;
      Assert((beentry->st_changecount & 1) == 0);
}

/*
 * Report current transaction start timestamp as the specified value.
 * Zero means there is no active transaction.
 */
void
pgstat_report_xact_timestamp(TimestampTz tstamp)
{
      volatile PgBackendStatus *beentry = MyBEEntry;

      if (!pgstat_track_activities || !beentry)
            return;

      /*
       * Update my status entry, following the protocol of bumping
       * st_changecount before and after.  We use a volatile pointer here to
       * ensure the compiler doesn't try to get cute.
       */
      beentry->st_changecount++;
      beentry->st_xact_start_timestamp = tstamp;
      beentry->st_changecount++;
      Assert((beentry->st_changecount & 1) == 0);
}

/* ----------
 * pgstat_report_waiting() -
 *
 *    Called from lock manager to report beginning or end of a lock wait.
 *
 * NB: this *must* be able to survive being called before MyBEEntry has been
 * initialized.
 * ----------
 */
void
pgstat_report_waiting(bool waiting)
{
      volatile PgBackendStatus *beentry = MyBEEntry;

      if (!pgstat_track_activities || !beentry)
            return;

      /*
       * Since this is a single-byte field in a struct that only this process
       * may modify, there seems no need to bother with the st_changecount
       * protocol.  The update must appear atomic in any case.
       */
      beentry->st_waiting = waiting;
}


/* ----------
 * pgstat_read_current_status() -
 *
 *    Copy the current contents of the PgBackendStatus array to local memory,
 *    if not already done in this transaction.
 * ----------
 */
static void
pgstat_read_current_status(void)
{
      volatile PgBackendStatus *beentry;
      PgBackendStatus *localtable;
      PgBackendStatus *localentry;
      char     *localactivity;
      int               i;

      Assert(!pgStatRunningInCollector);
      if (localBackendStatusTable)
            return;                             /* already done */

      pgstat_setup_memcxt();

      localtable = (PgBackendStatus *)
            MemoryContextAlloc(pgStatLocalContext,
                                       sizeof(PgBackendStatus) * MaxBackends);
      localactivity = (char *)
            MemoryContextAlloc(pgStatLocalContext,
                                       pgstat_track_activity_query_size * MaxBackends);
      localNumBackends = 0;

      beentry = BackendStatusArray;
      localentry = localtable;
      for (i = 1; i <= MaxBackends; i++)
      {
            /*
             * Follow the protocol of retrying if st_changecount changes while we
             * copy the entry, or if it's odd.  (The check for odd is needed to
             * cover the case where we are able to completely copy the entry while
             * the source backend is between increment steps.)    We use a volatile
             * pointer here to ensure the compiler doesn't try to get cute.
             */
            for (;;)
            {
                  int               save_changecount = beentry->st_changecount;

                  localentry->st_procpid = beentry->st_procpid;
                  if (localentry->st_procpid > 0)
                  {
                        memcpy(localentry, (char *) beentry, sizeof(PgBackendStatus));

                        /*
                         * strcpy is safe even if the string is modified concurrently,
                         * because there's always a \0 at the end of the buffer.
                         */
                        strcpy(localactivity, (char *) beentry->st_activity);
                        localentry->st_activity = localactivity;
                  }

                  if (save_changecount == beentry->st_changecount &&
                        (save_changecount & 1) == 0)
                        break;

                  /* Make sure we can break out of loop if stuck... */
                  CHECK_FOR_INTERRUPTS();
            }

            beentry++;
            /* Only valid entries get included into the local array */
            if (localentry->st_procpid > 0)
            {
                  localentry++;
                  localactivity += pgstat_track_activity_query_size;
                  localNumBackends++;
            }
      }

      /* Set the pointer only after completion of a valid table */
      localBackendStatusTable = localtable;
}


/* ----------
 * pgstat_get_backend_current_activity() -
 *
 *    Return a string representing the current activity of the backend with
 *    the specified PID.      This looks directly at the BackendStatusArray,
 *    and so will provide current information regardless of the age of our
 *    transaction's snapshot of the status array.
 *
 *    It is the caller's responsibility to invoke this only for backends whose
 *    state is expected to remain stable while the result is in use.    The
 *    only current use is in deadlock reporting, where we can expect that
 *    the target backend is blocked on a lock.  (There are corner cases
 *    where the target's wait could get aborted while we are looking at it,
 *    but the very worst consequence is to return a pointer to a string
 *    that's been changed, so we won't worry too much.)
 *
 *    Note: return strings for special cases match pg_stat_get_backend_activity.
 * ----------
 */
const char *
pgstat_get_backend_current_activity(int pid, bool checkUser)
{
      PgBackendStatus *beentry;
      int               i;

      beentry = BackendStatusArray;
      for (i = 1; i <= MaxBackends; i++)
      {
            /*
             * Although we expect the target backend's entry to be stable, that
             * doesn't imply that anyone else's is.  To avoid identifying the
             * wrong backend, while we check for a match to the desired PID we
             * must follow the protocol of retrying if st_changecount changes
             * while we examine the entry, or if it's odd.  (This might be
             * unnecessary, since fetching or storing an int is almost certainly
             * atomic, but let's play it safe.)  We use a volatile pointer here to
             * ensure the compiler doesn't try to get cute.
             */
            volatile PgBackendStatus *vbeentry = beentry;
            bool        found;

            for (;;)
            {
                  int               save_changecount = vbeentry->st_changecount;

                  found = (vbeentry->st_procpid == pid);

                  if (save_changecount == vbeentry->st_changecount &&
                        (save_changecount & 1) == 0)
                        break;

                  /* Make sure we can break out of loop if stuck... */
                  CHECK_FOR_INTERRUPTS();
            }

            if (found)
            {
                  /* Now it is safe to use the non-volatile pointer */
                  if (checkUser && !superuser() && beentry->st_userid != GetUserId())
                        return "<insufficient privilege>";
                  else if (*(beentry->st_activity) == '\0')
                        return "<command string not enabled>";
                  else
                        return beentry->st_activity;
            }

            beentry++;
      }

      /* If we get here, caller is in error ... */
      return "<backend information not available>";
}


/* ------------------------------------------------------------
 * Local support functions follow
 * ------------------------------------------------------------
 */


/* ----------
 * pgstat_setheader() -
 *
 *          Set common header fields in a statistics message
 * ----------
 */
static void
pgstat_setheader(PgStat_MsgHdr *hdr, StatMsgType mtype)
{
      hdr->m_type = mtype;
}


/* ----------
 * pgstat_send() -
 *
 *          Send out one statistics message to the collector
 * ----------
 */
static void
pgstat_send(void *msg, int len)
{
      int               rc;

      if (pgStatSock < 0)
            return;

      ((PgStat_MsgHdr *) msg)->m_size = len;

      /* We'll retry after EINTR, but ignore all other failures */
      do
      {
            rc = send(pgStatSock, msg, len, 0);
      } while (rc < 0 && errno == EINTR);

#ifdef USE_ASSERT_CHECKING
      /* In debug builds, log send failures ... */
      if (rc < 0)
            elog(LOG, "could not send to statistics collector: %m");
#endif
}

/* ----------
 * pgstat_send_bgwriter() -
 *
 *          Send bgwriter statistics to the collector
 * ----------
 */
void
pgstat_send_bgwriter(void)
{
      /* We assume this initializes to zeroes */
      static const PgStat_MsgBgWriter all_zeroes;

      /*
       * This function can be called even if nothing at all has happened. In
       * this case, avoid sending a completely empty message to the stats
       * collector.
       */
      if (memcmp(&BgWriterStats, &all_zeroes, sizeof(PgStat_MsgBgWriter)) == 0)
            return;

      /*
       * Prepare and send the message
       */
      pgstat_setheader(&BgWriterStats.m_hdr, PGSTAT_MTYPE_BGWRITER);
      pgstat_send(&BgWriterStats, sizeof(BgWriterStats));

      /*
       * Clear out the statistics buffer, so it can be re-used.
       */
      MemSet(&BgWriterStats, 0, sizeof(BgWriterStats));
}


/* ----------
 * PgstatCollectorMain() -
 *
 *    Start up the statistics collector process.      This is the body of the
 *    postmaster child process.
 *
 *    The argc/argv parameters are valid only in EXEC_BACKEND case.
 * ----------
 */
NON_EXEC_STATIC void
PgstatCollectorMain(int argc, char *argv[])
{
      int               len;
      PgStat_Msg  msg;

#ifndef WIN32
#ifdef HAVE_POLL
      struct pollfd input_fd;
#else
      struct timeval sel_timeout;
      fd_set            rfds;
#endif
#endif

      IsUnderPostmaster = true;     /* we are a postmaster subprocess now */

      MyProcPid = getpid();         /* reset MyProcPid */

      MyStartTime = time(NULL);     /* record Start Time for logging */

      /*
       * If possible, make this process a group leader, so that the postmaster
       * can signal any child processes too.    (pgstat probably never has any
       * child processes, but for consistency we make all postmaster child
       * processes do this.)
       */
#ifdef HAVE_SETSID
      if (setsid() < 0)
            elog(FATAL, "setsid() failed: %m");
#endif

      /*
       * Ignore all signals usually bound to some action in the postmaster,
       * except SIGQUIT.
       */
      pqsignal(SIGHUP, pgstat_sighup_handler);
      pqsignal(SIGINT, SIG_IGN);
      pqsignal(SIGTERM, SIG_IGN);
      pqsignal(SIGQUIT, pgstat_exit);
      pqsignal(SIGALRM, SIG_IGN);
      pqsignal(SIGPIPE, SIG_IGN);
      pqsignal(SIGUSR1, SIG_IGN);
      pqsignal(SIGUSR2, SIG_IGN);
      pqsignal(SIGCHLD, SIG_DFL);
      pqsignal(SIGTTIN, SIG_DFL);
      pqsignal(SIGTTOU, SIG_DFL);
      pqsignal(SIGCONT, SIG_DFL);
      pqsignal(SIGWINCH, SIG_DFL);
      PG_SETMASK(&UnBlockSig);

      /*
       * Identify myself via ps
       */
      init_ps_display("stats collector process", "", "", "");

      /*
       * Arrange to write the initial status file right away
       */
      last_statrequest = GetCurrentTimestamp();
      last_statwrite = last_statrequest - 1;

      /*
       * Read in an existing statistics stats file or initialize the stats to
       * zero.
       */
      pgStatRunningInCollector = true;
      pgStatDBHash = pgstat_read_statsfile(InvalidOid, true);

      /*
       * Setup the descriptor set for select(2).      Since only one bit in the set
       * ever changes, we need not repeat FD_ZERO each time.
       */
#if !defined(HAVE_POLL) && !defined(WIN32)
      FD_ZERO(&rfds);
#endif

      /*
       * Loop to process messages until we get SIGQUIT or detect ungraceful
       * death of our parent postmaster.
       *
       * For performance reasons, we don't want to do a PostmasterIsAlive() test
       * after every message; instead, do it only when select()/poll() is
       * interrupted by timeout.    In essence, we'll stay alive as long as
       * backends keep sending us stuff often, even if the postmaster is gone.
       */
      for (;;)
      {
            int               got_data;

            /*
             * Quit if we get SIGQUIT from the postmaster.
             */
            if (need_exit)
                  break;

            /*
             * Reload configuration if we got SIGHUP from the postmaster.
             */
            if (got_SIGHUP)
            {
                  ProcessConfigFile(PGC_SIGHUP);
                  got_SIGHUP = false;
            }

            /*
             * Write the stats file if a new request has arrived that is not
             * satisfied by existing file.
             */
            if (last_statwrite < last_statrequest)
                  pgstat_write_statsfile(false);

            /*
             * Wait for a message to arrive; but not for more than
             * PGSTAT_SELECT_TIMEOUT seconds. (This determines how quickly we will
             * shut down after an ungraceful postmaster termination; so it needn't
             * be very fast.  However, on some systems SIGQUIT won't interrupt the
             * poll/select call, so this also limits speed of response to SIGQUIT,
             * which is more important.)
             *
             * We use poll(2) if available, otherwise select(2). Win32 has its own
             * implementation.
             */
#ifndef WIN32
#ifdef HAVE_POLL
            input_fd.fd = pgStatSock;
            input_fd.events = POLLIN | POLLERR;
            input_fd.revents = 0;

            if (poll(&input_fd, 1, PGSTAT_SELECT_TIMEOUT * 1000) < 0)
            {
                  if (errno == EINTR)
                        continue;
                  ereport(ERROR,
                              (errcode_for_socket_access(),
                               errmsg("poll() failed in statistics collector: %m")));
            }

            got_data = (input_fd.revents != 0);
#else                                     /* !HAVE_POLL */

            FD_SET            (pgStatSock, &rfds);

            /*
             * timeout struct is modified by select() on some operating systems,
             * so re-fill it each time.
             */
            sel_timeout.tv_sec = PGSTAT_SELECT_TIMEOUT;
            sel_timeout.tv_usec = 0;

            if (select(pgStatSock + 1, &rfds, NULL, NULL, &sel_timeout) < 0)
            {
                  if (errno == EINTR)
                        continue;
                  ereport(ERROR,
                              (errcode_for_socket_access(),
                               errmsg("select() failed in statistics collector: %m")));
            }

            got_data = FD_ISSET(pgStatSock, &rfds);
#endif   /* HAVE_POLL */
#else                                     /* WIN32 */
            got_data = pgwin32_waitforsinglesocket(pgStatSock, FD_READ,
                                                                     PGSTAT_SELECT_TIMEOUT * 1000);
#endif

            /*
             * If there is a message on the socket, read it and check for
             * validity.
             */
            if (got_data)
            {
                  len = recv(pgStatSock, (char *) &msg,
                                 sizeof(PgStat_Msg), 0);
                  if (len < 0)
                  {
                        if (errno == EINTR)
                              continue;
                        ereport(ERROR,
                                    (errcode_for_socket_access(),
                                     errmsg("could not read statistics message: %m")));
                  }

                  /*
                   * We ignore messages that are smaller than our common header
                   */
                  if (len < sizeof(PgStat_MsgHdr))
                        continue;

                  /*
                   * The received length must match the length in the header
                   */
                  if (msg.msg_hdr.m_size != len)
                        continue;

                  /*
                   * O.K. - we accept this message.  Process it.
                   */
                  switch (msg.msg_hdr.m_type)
                  {
                        case PGSTAT_MTYPE_DUMMY:
                              break;

                        case PGSTAT_MTYPE_INQUIRY:
                              pgstat_recv_inquiry((PgStat_MsgInquiry *) &msg, len);
                              break;

                        case PGSTAT_MTYPE_TABSTAT:
                              pgstat_recv_tabstat((PgStat_MsgTabstat *) &msg, len);
                              break;

                        case PGSTAT_MTYPE_TABPURGE:
                              pgstat_recv_tabpurge((PgStat_MsgTabpurge *) &msg, len);
                              break;

                        case PGSTAT_MTYPE_DROPDB:
                              pgstat_recv_dropdb((PgStat_MsgDropdb *) &msg, len);
                              break;

                        case PGSTAT_MTYPE_RESETCOUNTER:
                              pgstat_recv_resetcounter((PgStat_MsgResetcounter *) &msg,
                                                                   len);
                              break;

                        case PGSTAT_MTYPE_AUTOVAC_START:
                              pgstat_recv_autovac((PgStat_MsgAutovacStart *) &msg, len);
                              break;

                        case PGSTAT_MTYPE_VACUUM:
                              pgstat_recv_vacuum((PgStat_MsgVacuum *) &msg, len);
                              break;

                        case PGSTAT_MTYPE_ANALYZE:
                              pgstat_recv_analyze((PgStat_MsgAnalyze *) &msg, len);
                              break;

                        case PGSTAT_MTYPE_BGWRITER:
                              pgstat_recv_bgwriter((PgStat_MsgBgWriter *) &msg, len);
                              break;

                        case PGSTAT_MTYPE_FUNCSTAT:
                              pgstat_recv_funcstat((PgStat_MsgFuncstat *) &msg, len);
                              break;

                        case PGSTAT_MTYPE_FUNCPURGE:
                              pgstat_recv_funcpurge((PgStat_MsgFuncpurge *) &msg, len);
                              break;

                        default:
                              break;
                  }
            }
            else
            {
                  /*
                   * We can only get here if the select/poll timeout elapsed. Check
                   * for postmaster death.
                   */
                  if (!PostmasterIsAlive(true))
                        break;
            }
      }                                         /* end of message-processing loop */

      /*
       * Save the final stats to reuse at next startup.
       */
      pgstat_write_statsfile(true);

      exit(0);
}


/* SIGQUIT signal handler for collector process */
static void
pgstat_exit(SIGNAL_ARGS)
{
      need_exit = true;
}

/* SIGHUP handler for collector process */
static void
pgstat_sighup_handler(SIGNAL_ARGS)
{
      got_SIGHUP = true;
}


/*
 * Lookup the hash table entry for the specified database. If no hash
 * table entry exists, initialize it, if the create parameter is true.
 * Else, return NULL.
 */
static PgStat_StatDBEntry *
pgstat_get_db_entry(Oid databaseid, bool create)
{
      PgStat_StatDBEntry *result;
      bool        found;
      HASHACTION  action = (create ? HASH_ENTER : HASH_FIND);

      /* Lookup or create the hash table entry for this database */
      result = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
                                                                        &databaseid,
                                                                        action, &found);

      if (!create && !found)
            return NULL;

      /* If not found, initialize the new one. */
      if (!found)
      {
            HASHCTL           hash_ctl;

            result->tables = NULL;
            result->functions = NULL;
            result->n_xact_commit = 0;
            result->n_xact_rollback = 0;
            result->n_blocks_fetched = 0;
            result->n_blocks_hit = 0;
            result->n_tuples_returned = 0;
            result->n_tuples_fetched = 0;
            result->n_tuples_inserted = 0;
            result->n_tuples_updated = 0;
            result->n_tuples_deleted = 0;
            result->last_autovac_time = 0;

            memset(&hash_ctl, 0, sizeof(hash_ctl));
            hash_ctl.keysize = sizeof(Oid);
            hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
            hash_ctl.hash = oid_hash;
            result->tables = hash_create("Per-database table",
                                                       PGSTAT_TAB_HASH_SIZE,
                                                       &hash_ctl,
                                                       HASH_ELEM | HASH_FUNCTION);

            hash_ctl.keysize = sizeof(Oid);
            hash_ctl.entrysize = sizeof(PgStat_StatFuncEntry);
            hash_ctl.hash = oid_hash;
            result->functions = hash_create("Per-database function",
                                                            PGSTAT_FUNCTION_HASH_SIZE,
                                                            &hash_ctl,
                                                            HASH_ELEM | HASH_FUNCTION);
      }

      return result;
}


/* ----------
 * pgstat_write_statsfile() -
 *
 *    Tell the news.
 *    If writing to the permanent file (happens when the collector is
 *    shutting down only), remove the temporary file so that backends
 *    starting up under a new postmaster can't read the old data before
 *    the new collector is ready.
 * ----------
 */
static void
pgstat_write_statsfile(bool permanent)
{
      HASH_SEQ_STATUS hstat;
      HASH_SEQ_STATUS tstat;
      HASH_SEQ_STATUS fstat;
      PgStat_StatDBEntry *dbentry;
      PgStat_StatTabEntry *tabentry;
      PgStat_StatFuncEntry *funcentry;
      FILE     *fpout;
      int32       format_id;
      const char *tmpfile = permanent ? PGSTAT_STAT_PERMANENT_TMPFILE : pgstat_stat_tmpname;
      const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;

      /*
       * Open the statistics temp file to write out the current values.
       */
      fpout = AllocateFile(tmpfile, PG_BINARY_W);
      if (fpout == NULL)
      {
            ereport(LOG,
                        (errcode_for_file_access(),
                         errmsg("could not open temporary statistics file \"%s\": %m",
                                    tmpfile)));
            return;
      }

      /*
       * Set the timestamp of the stats file.
       */
      globalStats.stats_timestamp = GetCurrentTimestamp();

      /*
       * Write the file header --- currently just a format ID.
       */
      format_id = PGSTAT_FILE_FORMAT_ID;
      fwrite(&format_id, sizeof(format_id), 1, fpout);

      /*
       * Write global stats struct
       */
      fwrite(&globalStats, sizeof(globalStats), 1, fpout);

      /*
       * Walk through the database table.
       */
      hash_seq_init(&hstat, pgStatDBHash);
      while ((dbentry = (PgStat_StatDBEntry *) hash_seq_search(&hstat)) != NULL)
      {
            /*
             * Write out the DB entry including the number of live backends. We
             * don't write the tables or functions pointers, since they're of no
             * use to any other process.
             */
            fputc('D', fpout);
            fwrite(dbentry, offsetof(PgStat_StatDBEntry, tables), 1, fpout);

            /*
             * Walk through the database's access stats per table.
             */
            hash_seq_init(&tstat, dbentry->tables);
            while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&tstat)) != NULL)
            {
                  fputc('T', fpout);
                  fwrite(tabentry, sizeof(PgStat_StatTabEntry), 1, fpout);
            }

            /*
             * Walk through the database's function stats table.
             */
            hash_seq_init(&fstat, dbentry->functions);
            while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&fstat)) != NULL)
            {
                  fputc('F', fpout);
                  fwrite(funcentry, sizeof(PgStat_StatFuncEntry), 1, fpout);
            }

            /*
             * Mark the end of this DB
             */
            fputc('d', fpout);
      }

      /*
       * No more output to be done. Close the temp file and replace the old
       * pgstat.stat with it.  The ferror() check replaces testing for error
       * after each individual fputc or fwrite above.
       */
      fputc('E', fpout);

      if (ferror(fpout))
      {
            ereport(LOG,
                        (errcode_for_file_access(),
                     errmsg("could not write temporary statistics file \"%s\": %m",
                                tmpfile)));
            FreeFile(fpout);
            unlink(tmpfile);
      }
      else if (FreeFile(fpout) < 0)
      {
            ereport(LOG,
                        (errcode_for_file_access(),
                     errmsg("could not close temporary statistics file \"%s\": %m",
                                tmpfile)));
            unlink(tmpfile);
      }
      else if (rename(tmpfile, statfile) < 0)
      {
            ereport(LOG,
                        (errcode_for_file_access(),
                         errmsg("could not rename temporary statistics file \"%s\" to \"%s\": %m",
                                    tmpfile, statfile)));
            unlink(tmpfile);
      }
      else
      {
            /*
             * Successful write, so update last_statwrite.
             */
            last_statwrite = globalStats.stats_timestamp;

            /*
             * It's not entirely clear whether there could be clock skew between
             * backends and the collector; but just in case someone manages to
             * send us a stats request time that's far in the future, reset it.
             * This ensures that no inquiry message can cause more than one stats
             * file write to occur.
             */
            last_statrequest = last_statwrite;
      }

      if (permanent)
            unlink(pgstat_stat_filename);
}


/* ----------
 * pgstat_read_statsfile() -
 *
 *    Reads in an existing statistics collector file and initializes the
 *    databases' hash table (whose entries point to the tables' hash tables).
 * ----------
 */
static HTAB *
pgstat_read_statsfile(Oid onlydb, bool permanent)
{
      PgStat_StatDBEntry *dbentry;
      PgStat_StatDBEntry dbbuf;
      PgStat_StatTabEntry *tabentry;
      PgStat_StatTabEntry tabbuf;
      PgStat_StatFuncEntry funcbuf;
      PgStat_StatFuncEntry *funcentry;
      HASHCTL           hash_ctl;
      HTAB     *dbhash;
      HTAB     *tabhash = NULL;
      HTAB     *funchash = NULL;
      FILE     *fpin;
      int32       format_id;
      bool        found;
      const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;

      /*
       * The tables will live in pgStatLocalContext.
       */
      pgstat_setup_memcxt();

      /*
       * Create the DB hashtable
       */
      memset(&hash_ctl, 0, sizeof(hash_ctl));
      hash_ctl.keysize = sizeof(Oid);
      hash_ctl.entrysize = sizeof(PgStat_StatDBEntry);
      hash_ctl.hash = oid_hash;
      hash_ctl.hcxt = pgStatLocalContext;
      dbhash = hash_create("Databases hash", PGSTAT_DB_HASH_SIZE, &hash_ctl,
                                     HASH_ELEM | HASH_FUNCTION | HASH_CONTEXT);

      /*
       * Clear out global statistics so they start from zero in case we can't
       * load an existing statsfile.
       */
      memset(&globalStats, 0, sizeof(globalStats));

      /*
       * Try to open the status file. If it doesn't exist, the backends simply
       * return zero for anything and the collector simply starts from scratch
       * with empty counters.
       */
      if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
            return dbhash;

      /*
       * Verify it's of the expected format.
       */
      if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id)
            || format_id != PGSTAT_FILE_FORMAT_ID)
      {
            ereport(pgStatRunningInCollector ? LOG : WARNING,
                        (errmsg("corrupted pgstat.stat file")));
            goto done;
      }

      /*
       * Read global stats struct
       */
      if (fread(&globalStats, 1, sizeof(globalStats), fpin) != sizeof(globalStats))
      {
            ereport(pgStatRunningInCollector ? LOG : WARNING,
                        (errmsg("corrupted pgstat.stat file")));
            goto done;
      }

      /*
       * We found an existing collector stats file. Read it and put all the
       * hashtable entries into place.
       */
      for (;;)
      {
            switch (fgetc(fpin))
            {
                        /*
                         * 'D'      A PgStat_StatDBEntry struct describing a database
                         * follows. Subsequently, zero to many 'T' and 'F' entries
                         * will follow until a 'd' is encountered.
                         */
                  case 'D':
                        if (fread(&dbbuf, 1, offsetof(PgStat_StatDBEntry, tables),
                                      fpin) != offsetof(PgStat_StatDBEntry, tables))
                        {
                              ereport(pgStatRunningInCollector ? LOG : WARNING,
                                          (errmsg("corrupted pgstat.stat file")));
                              goto done;
                        }

                        /*
                         * Add to the DB hash
                         */
                        dbentry = (PgStat_StatDBEntry *) hash_search(dbhash,
                                                                          (void *) &dbbuf.databaseid,
                                                                                           HASH_ENTER,
                                                                                           &found);
                        if (found)
                        {
                              ereport(pgStatRunningInCollector ? LOG : WARNING,
                                          (errmsg("corrupted pgstat.stat file")));
                              goto done;
                        }

                        memcpy(dbentry, &dbbuf, sizeof(PgStat_StatDBEntry));
                        dbentry->tables = NULL;
                        dbentry->functions = NULL;

                        /*
                         * Don't collect tables if not the requested DB (or the
                         * shared-table info)
                         */
                        if (onlydb != InvalidOid)
                        {
                              if (dbbuf.databaseid != onlydb &&
                                    dbbuf.databaseid != InvalidOid)
                                    break;
                        }

                        memset(&hash_ctl, 0, sizeof(hash_ctl));
                        hash_ctl.keysize = sizeof(Oid);
                        hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
                        hash_ctl.hash = oid_hash;
                        hash_ctl.hcxt = pgStatLocalContext;
                        dbentry->tables = hash_create("Per-database table",
                                                                    PGSTAT_TAB_HASH_SIZE,
                                                                    &hash_ctl,
                                                   HASH_ELEM | HASH_FUNCTION | HASH_CONTEXT);

                        hash_ctl.keysize = sizeof(Oid);
                        hash_ctl.entrysize = sizeof(PgStat_StatFuncEntry);
                        hash_ctl.hash = oid_hash;
                        hash_ctl.hcxt = pgStatLocalContext;
                        dbentry->functions = hash_create("Per-database function",
                                                                         PGSTAT_FUNCTION_HASH_SIZE,
                                                                         &hash_ctl,
                                                   HASH_ELEM | HASH_FUNCTION | HASH_CONTEXT);

                        /*
                         * Arrange that following records add entries to this
                         * database's hash tables.
                         */
                        tabhash = dbentry->tables;
                        funchash = dbentry->functions;
                        break;

                        /*
                         * 'd'      End of this database.
                         */
                  case 'd':
                        tabhash = NULL;
                        funchash = NULL;
                        break;

                        /*
                         * 'T'      A PgStat_StatTabEntry follows.
                         */
                  case 'T':
                        if (fread(&tabbuf, 1, sizeof(PgStat_StatTabEntry),
                                      fpin) != sizeof(PgStat_StatTabEntry))
                        {
                              ereport(pgStatRunningInCollector ? LOG : WARNING,
                                          (errmsg("corrupted pgstat.stat file")));
                              goto done;
                        }

                        /*
                         * Skip if table belongs to a not requested database.
                         */
                        if (tabhash == NULL)
                              break;

                        tabentry = (PgStat_StatTabEntry *) hash_search(tabhash,
                                                                              (void *) &tabbuf.tableid,
                                                                                     HASH_ENTER, &found);

                        if (found)
                        {
                              ereport(pgStatRunningInCollector ? LOG : WARNING,
                                          (errmsg("corrupted pgstat.stat file")));
                              goto done;
                        }

                        memcpy(tabentry, &tabbuf, sizeof(tabbuf));
                        break;

                        /*
                         * 'F'      A PgStat_StatFuncEntry follows.
                         */
                  case 'F':
                        if (fread(&funcbuf, 1, sizeof(PgStat_StatFuncEntry),
                                      fpin) != sizeof(PgStat_StatFuncEntry))
                        {
                              ereport(pgStatRunningInCollector ? LOG : WARNING,
                                          (errmsg("corrupted pgstat.stat file")));
                              goto done;
                        }

                        /*
                         * Skip if function belongs to a not requested database.
                         */
                        if (funchash == NULL)
                              break;

                        funcentry = (PgStat_StatFuncEntry *) hash_search(funchash,
                                                                        (void *) &funcbuf.functionid,
                                                                                     HASH_ENTER, &found);

                        if (found)
                        {
                              ereport(pgStatRunningInCollector ? LOG : WARNING,
                                          (errmsg("corrupted pgstat.stat file")));
                              goto done;
                        }

                        memcpy(funcentry, &funcbuf, sizeof(funcbuf));
                        break;

                        /*
                         * 'E'      The EOF marker of a complete stats file.
                         */
                  case 'E':
                        goto done;

                  default:
                        ereport(pgStatRunningInCollector ? LOG : WARNING,
                                    (errmsg("corrupted pgstat.stat file")));
                        goto done;
            }
      }

done:
      FreeFile(fpin);

      if (permanent)
            unlink(PGSTAT_STAT_PERMANENT_FILENAME);

      return dbhash;
}

/* ----------
 * pgstat_read_statsfile_timestamp() -
 *
 *    Attempt to fetch the timestamp of an existing stats file.
 *    Returns TRUE if successful (timestamp is stored at *ts).
 * ----------
 */
static bool
pgstat_read_statsfile_timestamp(bool permanent, TimestampTz *ts)
{
      PgStat_GlobalStats myGlobalStats;
      FILE     *fpin;
      int32       format_id;
      const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;

      /*
       * Try to open the status file.
       */
      if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
            return false;

      /*
       * Verify it's of the expected format.
       */
      if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id)
            || format_id != PGSTAT_FILE_FORMAT_ID)
      {
            FreeFile(fpin);
            return false;
      }

      /*
       * Read global stats struct
       */
      if (fread(&myGlobalStats, 1, sizeof(myGlobalStats), fpin) != sizeof(myGlobalStats))
      {
            FreeFile(fpin);
            return false;
      }

      *ts = myGlobalStats.stats_timestamp;

      FreeFile(fpin);
      return true;
}

/*
 * If not already done, read the statistics collector stats file into
 * some hash tables.  The results will be kept until pgstat_clear_snapshot()
 * is called (typically, at end of transaction).
 */
static void
backend_read_statsfile(void)
{
      TimestampTz min_ts;
      int               count;

      /* already read it? */
      if (pgStatDBHash)
            return;
      Assert(!pgStatRunningInCollector);

      /*
       * We set the minimum acceptable timestamp to PGSTAT_STAT_INTERVAL msec
       * before now.    This indirectly ensures that the collector needn't write
       * the file more often than PGSTAT_STAT_INTERVAL.  In an autovacuum
       * worker, however, we want a lower delay to avoid using stale data, so we
       * use PGSTAT_RETRY_DELAY (since the number of worker is low, this
       * shouldn't be a problem).
       *
       * Note that we don't recompute min_ts after sleeping; so we might end up
       * accepting a file a bit older than PGSTAT_STAT_INTERVAL.  In practice
       * that shouldn't happen, though, as long as the sleep time is less than
       * PGSTAT_STAT_INTERVAL; and we don't want to lie to the collector about
       * what our cutoff time really is.
       */
      if (IsAutoVacuumWorkerProcess())
            min_ts = TimestampTzPlusMilliseconds(GetCurrentTimestamp(),
                                                                   -PGSTAT_RETRY_DELAY);
      else
            min_ts = TimestampTzPlusMilliseconds(GetCurrentTimestamp(),
                                                                   -PGSTAT_STAT_INTERVAL);

      /*
       * Loop until fresh enough stats file is available or we ran out of time.
       * The stats inquiry message is sent repeatedly in case collector drops
       * it.
       */
      for (count = 0; count < PGSTAT_POLL_LOOP_COUNT; count++)
      {
            TimestampTz file_ts = 0;

            CHECK_FOR_INTERRUPTS();

            if (pgstat_read_statsfile_timestamp(false, &file_ts) &&
                  file_ts >= min_ts)
                  break;

            /* Not there or too old, so kick the collector and wait a bit */
            pgstat_send_inquiry(min_ts);
            pg_usleep(PGSTAT_RETRY_DELAY * 1000L);
      }

      if (count >= PGSTAT_POLL_LOOP_COUNT)
            elog(WARNING, "pgstat wait timeout");

      /* Autovacuum launcher wants stats about all databases */
      if (IsAutoVacuumLauncherProcess())
            pgStatDBHash = pgstat_read_statsfile(InvalidOid, false);
      else
            pgStatDBHash = pgstat_read_statsfile(MyDatabaseId, false);
}


/* ----------
 * pgstat_setup_memcxt() -
 *
 *    Create pgStatLocalContext, if not already done.
 * ----------
 */
static void
pgstat_setup_memcxt(void)
{
      if (!pgStatLocalContext)
            pgStatLocalContext = AllocSetContextCreate(TopMemoryContext,
                                                                           "Statistics snapshot",
                                                                           ALLOCSET_SMALL_MINSIZE,
                                                                           ALLOCSET_SMALL_INITSIZE,
                                                                           ALLOCSET_SMALL_MAXSIZE);
}


/* ----------
 * pgstat_clear_snapshot() -
 *
 *    Discard any data collected in the current transaction.      Any subsequent
 *    request will cause new snapshots to be read.
 *
 *    This is also invoked during transaction commit or abort to discard
 *    the no-longer-wanted snapshot.
 * ----------
 */
void
pgstat_clear_snapshot(void)
{
      /* Release memory, if any was allocated */
      if (pgStatLocalContext)
            MemoryContextDelete(pgStatLocalContext);

      /* Reset variables */
      pgStatLocalContext = NULL;
      pgStatDBHash = NULL;
      localBackendStatusTable = NULL;
      localNumBackends = 0;
}


/* ----------
 * pgstat_recv_inquiry() -
 *
 *    Process stat inquiry requests.
 * ----------
 */
static void
pgstat_recv_inquiry(PgStat_MsgInquiry *msg, int len)
{
      if (msg->inquiry_time > last_statrequest)
            last_statrequest = msg->inquiry_time;
}


/* ----------
 * pgstat_recv_tabstat() -
 *
 *    Count what the backend has done.
 * ----------
 */
static void
pgstat_recv_tabstat(PgStat_MsgTabstat *msg, int len)
{
      PgStat_TableEntry *tabmsg = &(msg->m_entry[0]);
      PgStat_StatDBEntry *dbentry;
      PgStat_StatTabEntry *tabentry;
      int               i;
      bool        found;

      dbentry = pgstat_get_db_entry(msg->m_databaseid, true);

      /*
       * Update database-wide stats.
       */
      dbentry->n_xact_commit += (PgStat_Counter) (msg->m_xact_commit);
      dbentry->n_xact_rollback += (PgStat_Counter) (msg->m_xact_rollback);

      /*
       * Process all table entries in the message.
       */
      for (i = 0; i < msg->m_nentries; i++)
      {
            tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
                                                                          (void *) &(tabmsg[i].t_id),
                                                                                 HASH_ENTER, &found);

            if (!found)
            {
                  /*
                   * If it's a new table entry, initialize counters to the values we
                   * just got.
                   */
                  tabentry->numscans = tabmsg[i].t_counts.t_numscans;
                  tabentry->tuples_returned = tabmsg[i].t_counts.t_tuples_returned;
                  tabentry->tuples_fetched = tabmsg[i].t_counts.t_tuples_fetched;
                  tabentry->tuples_inserted = tabmsg[i].t_counts.t_tuples_inserted;
                  tabentry->tuples_updated = tabmsg[i].t_counts.t_tuples_updated;
                  tabentry->tuples_deleted = tabmsg[i].t_counts.t_tuples_deleted;
                  tabentry->tuples_hot_updated = tabmsg[i].t_counts.t_tuples_hot_updated;
                  tabentry->n_live_tuples = tabmsg[i].t_counts.t_new_live_tuples;
                  tabentry->n_dead_tuples = tabmsg[i].t_counts.t_new_dead_tuples;
                  tabentry->blocks_fetched = tabmsg[i].t_counts.t_blocks_fetched;
                  tabentry->blocks_hit = tabmsg[i].t_counts.t_blocks_hit;

                  tabentry->last_anl_tuples = 0;
                  tabentry->vacuum_timestamp = 0;
                  tabentry->autovac_vacuum_timestamp = 0;
                  tabentry->analyze_timestamp = 0;
                  tabentry->autovac_analyze_timestamp = 0;
            }
            else
            {
                  /*
                   * Otherwise add the values to the existing entry.
                   */
                  tabentry->numscans += tabmsg[i].t_counts.t_numscans;
                  tabentry->tuples_returned += tabmsg[i].t_counts.t_tuples_returned;
                  tabentry->tuples_fetched += tabmsg[i].t_counts.t_tuples_fetched;
                  tabentry->tuples_inserted += tabmsg[i].t_counts.t_tuples_inserted;
                  tabentry->tuples_updated += tabmsg[i].t_counts.t_tuples_updated;
                  tabentry->tuples_deleted += tabmsg[i].t_counts.t_tuples_deleted;
                  tabentry->tuples_hot_updated += tabmsg[i].t_counts.t_tuples_hot_updated;
                  tabentry->n_live_tuples += tabmsg[i].t_counts.t_new_live_tuples;
                  tabentry->n_dead_tuples += tabmsg[i].t_counts.t_new_dead_tuples;
                  tabentry->blocks_fetched += tabmsg[i].t_counts.t_blocks_fetched;
                  tabentry->blocks_hit += tabmsg[i].t_counts.t_blocks_hit;
            }

            /* Clamp n_live_tuples in case of negative new_live_tuples */
            tabentry->n_live_tuples = Max(tabentry->n_live_tuples, 0);
            /* Likewise for n_dead_tuples */
            tabentry->n_dead_tuples = Max(tabentry->n_dead_tuples, 0);

            /*
             * Add per-table stats to the per-database entry, too.
             */
            dbentry->n_tuples_returned += tabmsg[i].t_counts.t_tuples_returned;
            dbentry->n_tuples_fetched += tabmsg[i].t_counts.t_tuples_fetched;
            dbentry->n_tuples_inserted += tabmsg[i].t_counts.t_tuples_inserted;
            dbentry->n_tuples_updated += tabmsg[i].t_counts.t_tuples_updated;
            dbentry->n_tuples_deleted += tabmsg[i].t_counts.t_tuples_deleted;
            dbentry->n_blocks_fetched += tabmsg[i].t_counts.t_blocks_fetched;
            dbentry->n_blocks_hit += tabmsg[i].t_counts.t_blocks_hit;
      }
}


/* ----------
 * pgstat_recv_tabpurge() -
 *
 *    Arrange for dead table removal.
 * ----------
 */
static void
pgstat_recv_tabpurge(PgStat_MsgTabpurge *msg, int len)
{
      PgStat_StatDBEntry *dbentry;
      int               i;

      dbentry = pgstat_get_db_entry(msg->m_databaseid, false);

      /*
       * No need to purge if we don't even know the database.
       */
      if (!dbentry || !dbentry->tables)
            return;

      /*
       * Process all table entries in the message.
       */
      for (i = 0; i < msg->m_nentries; i++)
      {
            /* Remove from hashtable if present; we don't care if it's not. */
            (void) hash_search(dbentry->tables,
                                       (void *) &(msg->m_tableid[i]),
                                       HASH_REMOVE, NULL);
      }
}


/* ----------
 * pgstat_recv_dropdb() -
 *
 *    Arrange for dead database removal
 * ----------
 */
static void
pgstat_recv_dropdb(PgStat_MsgDropdb *msg, int len)
{
      PgStat_StatDBEntry *dbentry;

      /*
       * Lookup the database in the hashtable.
       */
      dbentry = pgstat_get_db_entry(msg->m_databaseid, false);

      /*
       * If found, remove it.
       */
      if (dbentry)
      {
            if (dbentry->tables != NULL)
                  hash_destroy(dbentry->tables);
            if (dbentry->functions != NULL)
                  hash_destroy(dbentry->functions);

            if (hash_search(pgStatDBHash,
                                    (void *) &(dbentry->databaseid),
                                    HASH_REMOVE, NULL) == NULL)
                  ereport(ERROR,
                              (errmsg("database hash table corrupted "
                                          "during cleanup --- abort")));
      }
}


/* ----------
 * pgstat_recv_resetcounter() -
 *
 *    Reset the statistics for the specified database.
 * ----------
 */
static void
pgstat_recv_resetcounter(PgStat_MsgResetcounter *msg, int len)
{
      HASHCTL           hash_ctl;
      PgStat_StatDBEntry *dbentry;

      /*
       * Lookup the database in the hashtable.  Nothing to do if not there.
       */
      dbentry = pgstat_get_db_entry(msg->m_databaseid, false);

      if (!dbentry)
            return;

      /*
       * We simply throw away all the database's table entries by recreating a
       * new hash table for them.
       */
      if (dbentry->tables != NULL)
            hash_destroy(dbentry->tables);
      if (dbentry->functions != NULL)
            hash_destroy(dbentry->functions);

      dbentry->tables = NULL;
      dbentry->functions = NULL;
      dbentry->n_xact_commit = 0;
      dbentry->n_xact_rollback = 0;
      dbentry->n_blocks_fetched = 0;
      dbentry->n_blocks_hit = 0;

      memset(&hash_ctl, 0, sizeof(hash_ctl));
      hash_ctl.keysize = sizeof(Oid);
      hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
      hash_ctl.hash = oid_hash;
      dbentry->tables = hash_create("Per-database table",
                                                  PGSTAT_TAB_HASH_SIZE,
                                                  &hash_ctl,
                                                  HASH_ELEM | HASH_FUNCTION);

      hash_ctl.keysize = sizeof(Oid);
      hash_ctl.entrysize = sizeof(PgStat_StatFuncEntry);
      hash_ctl.hash = oid_hash;
      dbentry->functions = hash_create("Per-database function",
                                                       PGSTAT_FUNCTION_HASH_SIZE,
                                                       &hash_ctl,
                                                       HASH_ELEM | HASH_FUNCTION);
}

/* ----------
 * pgstat_recv_autovac() -
 *
 *    Process an autovacuum signalling message.
 * ----------
 */
static void
pgstat_recv_autovac(PgStat_MsgAutovacStart *msg, int len)
{
      PgStat_StatDBEntry *dbentry;

      /*
       * Lookup the database in the hashtable.  Don't create the entry if it
       * doesn't exist, because autovacuum may be processing a template
       * database.  If this isn't the case, the database is most likely to have
       * an entry already.  (If it doesn't, not much harm is done anyway --
       * it'll get created as soon as somebody actually uses the database.)
       */
      dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
      if (dbentry == NULL)
            return;

      /*
       * Store the last autovacuum time in the database entry.
       */
      dbentry->last_autovac_time = msg->m_start_time;
}

/* ----------
 * pgstat_recv_vacuum() -
 *
 *    Process a VACUUM message.
 * ----------
 */
static void
pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len)
{
      PgStat_StatDBEntry *dbentry;
      PgStat_StatTabEntry *tabentry;

      /*
       * Don't create either the database or table entry if it doesn't already
       * exist.  This avoids bloating the stats with entries for stuff that is
       * only touched by vacuum and not by live operations.
       */
      dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
      if (dbentry == NULL)
            return;

      tabentry = hash_search(dbentry->tables, &(msg->m_tableoid),
                                       HASH_FIND, NULL);
      if (tabentry == NULL)
            return;

      if (msg->m_autovacuum)
            tabentry->autovac_vacuum_timestamp = msg->m_vacuumtime;
      else
            tabentry->vacuum_timestamp = msg->m_vacuumtime;
      if (msg->m_scanned_all)
            tabentry->n_live_tuples = msg->m_tuples;
      /* Resetting dead_tuples to 0 is an approximation ... */
      tabentry->n_dead_tuples = 0;
      if (msg->m_analyze)
      {
            if (msg->m_scanned_all)
                  tabentry->last_anl_tuples = msg->m_tuples;
            else
            {
                  /* last_anl_tuples must never exceed n_live_tuples+n_dead_tuples */
                  tabentry->last_anl_tuples = Min(tabentry->last_anl_tuples,
                                                                  tabentry->n_live_tuples);
            }

            if (msg->m_autovacuum)
                  tabentry->autovac_analyze_timestamp = msg->m_vacuumtime;
            else
                  tabentry->analyze_timestamp = msg->m_vacuumtime;
      }
      else
      {
            /* last_anl_tuples must never exceed n_live_tuples+n_dead_tuples */
            tabentry->last_anl_tuples = Min(tabentry->last_anl_tuples,
                                                            tabentry->n_live_tuples);
      }
}

/* ----------
 * pgstat_recv_analyze() -
 *
 *    Process an ANALYZE message.
 * ----------
 */
static void
pgstat_recv_analyze(PgStat_MsgAnalyze *msg, int len)
{
      PgStat_StatDBEntry *dbentry;
      PgStat_StatTabEntry *tabentry;

      /*
       * Don't create either the database or table entry if it doesn't already
       * exist.  This avoids bloating the stats with entries for stuff that is
       * only touched by analyze and not by live operations.
       */
      dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
      if (dbentry == NULL)
            return;

      tabentry = hash_search(dbentry->tables, &(msg->m_tableoid),
                                       HASH_FIND, NULL);
      if (tabentry == NULL)
            return;

      if (msg->m_autovacuum)
            tabentry->autovac_analyze_timestamp = msg->m_analyzetime;
      else
            tabentry->analyze_timestamp = msg->m_analyzetime;
      tabentry->n_live_tuples = msg->m_live_tuples;
      tabentry->n_dead_tuples = msg->m_dead_tuples;
      tabentry->last_anl_tuples = msg->m_live_tuples + msg->m_dead_tuples;
}


/* ----------
 * pgstat_recv_bgwriter() -
 *
 *    Process a BGWRITER message.
 * ----------
 */
static void
pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len)
{
      globalStats.timed_checkpoints += msg->m_timed_checkpoints;
      globalStats.requested_checkpoints += msg->m_requested_checkpoints;
      globalStats.buf_written_checkpoints += msg->m_buf_written_checkpoints;
      globalStats.buf_written_clean += msg->m_buf_written_clean;
      globalStats.maxwritten_clean += msg->m_maxwritten_clean;
      globalStats.buf_written_backend += msg->m_buf_written_backend;
      globalStats.buf_alloc += msg->m_buf_alloc;
}

/* ----------
 * pgstat_recv_funcstat() -
 *
 *    Count what the backend has done.
 * ----------
 */
static void
pgstat_recv_funcstat(PgStat_MsgFuncstat *msg, int len)
{
      PgStat_FunctionEntry *funcmsg = &(msg->m_entry[0]);
      PgStat_StatDBEntry *dbentry;
      PgStat_StatFuncEntry *funcentry;
      int               i;
      bool        found;

      dbentry = pgstat_get_db_entry(msg->m_databaseid, true);

      /*
       * Process all function entries in the message.
       */
      for (i = 0; i < msg->m_nentries; i++, funcmsg++)
      {
            funcentry = (PgStat_StatFuncEntry *) hash_search(dbentry->functions,
                                                                           (void *) &(funcmsg->f_id),
                                                                                     HASH_ENTER, &found);

            if (!found)
            {
                  /*
                   * If it's a new function entry, initialize counters to the values
                   * we just got.
                   */
                  funcentry->f_numcalls = funcmsg->f_numcalls;
                  funcentry->f_time = funcmsg->f_time;
                  funcentry->f_time_self = funcmsg->f_time_self;
            }
            else
            {
                  /*
                   * Otherwise add the values to the existing entry.
                   */
                  funcentry->f_numcalls += funcmsg->f_numcalls;
                  funcentry->f_time += funcmsg->f_time;
                  funcentry->f_time_self += funcmsg->f_time_self;
            }
      }
}

/* ----------
 * pgstat_recv_funcpurge() -
 *
 *    Arrange for dead function removal.
 * ----------
 */
static void
pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len)
{
      PgStat_StatDBEntry *dbentry;
      int               i;

      dbentry = pgstat_get_db_entry(msg->m_databaseid, false);

      /*
       * No need to purge if we don't even know the database.
       */
      if (!dbentry || !dbentry->functions)
            return;

      /*
       * Process all function entries in the message.
       */
      for (i = 0; i < msg->m_nentries; i++)
      {
            /* Remove from hashtable if present; we don't care if it's not. */
            (void) hash_search(dbentry->functions,
                                       (void *) &(msg->m_functionid[i]),
                                       HASH_REMOVE, NULL);
      }
}

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