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Sourcecode: postgresql-8.4 version File versions

sequence.c

/*-------------------------------------------------------------------------
 *
 * sequence.c
 *      PostgreSQL sequences support code.
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *      $PostgreSQL$
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/heapam.h"
#include "access/transam.h"
#include "access/xact.h"
#include "access/xlogutils.h"
#include "catalog/dependency.h"
#include "catalog/namespace.h"
#include "catalog/pg_type.h"
#include "commands/defrem.h"
#include "commands/sequence.h"
#include "commands/tablecmds.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "storage/bufmgr.h"
#include "storage/lmgr.h"
#include "storage/proc.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/resowner.h"
#include "utils/syscache.h"


/*
 * We don't want to log each fetching of a value from a sequence,
 * so we pre-log a few fetches in advance. In the event of
 * crash we can lose as much as we pre-logged.
 */
#define SEQ_LOG_VALS    32

/*
 * The "special area" of a sequence's buffer page looks like this.
 */
#define SEQ_MAGIC   0x1717

typedef struct sequence_magic
{
      uint32            magic;
} sequence_magic;

/*
 * We store a SeqTable item for every sequence we have touched in the current
 * session.  This is needed to hold onto nextval/currval state.  (We can't
 * rely on the relcache, since it's only, well, a cache, and may decide to
 * discard entries.)
 *
 * XXX We use linear search to find pre-existing SeqTable entries.      This is
 * good when only a small number of sequences are touched in a session, but
 * would suck with many different sequences.  Perhaps use a hashtable someday.
 */
typedef struct SeqTableData
{
      struct SeqTableData *next;    /* link to next SeqTable object */
      Oid               relid;                  /* pg_class OID of this sequence */
      LocalTransactionId lxid;      /* xact in which we last did a seq op */
      bool        last_valid;       /* do we have a valid "last" value? */
      int64       last;             /* value last returned by nextval */
      int64       cached;                 /* last value already cached for nextval */
      /* if last != cached, we have not used up all the cached values */
      int64       increment;        /* copy of sequence's increment field */
      /* note that increment is zero until we first do read_info() */
} SeqTableData;

typedef SeqTableData *SeqTable;

static SeqTable seqtab = NULL;      /* Head of list of SeqTable items */

/*
 * last_used_seq is updated by nextval() to point to the last used
 * sequence.
 */
static SeqTableData *last_used_seq = NULL;

static int64 nextval_internal(Oid relid);
static Relation open_share_lock(SeqTable seq);
static void init_sequence(Oid relid, SeqTable *p_elm, Relation *p_rel);
static Form_pg_sequence read_info(SeqTable elm, Relation rel, Buffer *buf);
static void init_params(List *options, bool isInit,
                  Form_pg_sequence new, List **owned_by);
static void do_setval(Oid relid, int64 next, bool iscalled);
static void process_owned_by(Relation seqrel, List *owned_by);


/*
 * DefineSequence
 *                      Creates a new sequence relation
 */
void
DefineSequence(CreateSeqStmt *seq)
{
      FormData_pg_sequence new;
      List     *owned_by;
      CreateStmt *stmt = makeNode(CreateStmt);
      Oid               seqoid;
      Relation    rel;
      Buffer            buf;
      Page        page;
      sequence_magic *sm;
      HeapTuple   tuple;
      TupleDesc   tupDesc;
      Datum       value[SEQ_COL_LASTCOL];
      bool        null[SEQ_COL_LASTCOL];
      int               i;
      NameData    name;

      /* Check and set all option values */
      init_params(seq->options, true, &new, &owned_by);

      /*
       * Create relation (and fill value[] and null[] for the tuple)
       */
      stmt->tableElts = NIL;
      for (i = SEQ_COL_FIRSTCOL; i <= SEQ_COL_LASTCOL; i++)
      {
            ColumnDef  *coldef = makeNode(ColumnDef);

            coldef->inhcount = 0;
            coldef->is_local = true;
            coldef->is_not_null = true;
            coldef->raw_default = NULL;
            coldef->cooked_default = NULL;
            coldef->constraints = NIL;

            null[i - 1] = false;

            switch (i)
            {
                  case SEQ_COL_NAME:
                        coldef->typename = makeTypeNameFromOid(NAMEOID, -1);
                        coldef->colname = "sequence_name";
                        namestrcpy(&name, seq->sequence->relname);
                        value[i - 1] = NameGetDatum(&name);
                        break;
                  case SEQ_COL_LASTVAL:
                        coldef->typename = makeTypeNameFromOid(INT8OID, -1);
                        coldef->colname = "last_value";
                        value[i - 1] = Int64GetDatumFast(new.last_value);
                        break;
                  case SEQ_COL_STARTVAL:
                        coldef->typename = makeTypeNameFromOid(INT8OID, -1);
                        coldef->colname = "start_value";
                        value[i - 1] = Int64GetDatumFast(new.start_value);
                        break;
                  case SEQ_COL_INCBY:
                        coldef->typename = makeTypeNameFromOid(INT8OID, -1);
                        coldef->colname = "increment_by";
                        value[i - 1] = Int64GetDatumFast(new.increment_by);
                        break;
                  case SEQ_COL_MAXVALUE:
                        coldef->typename = makeTypeNameFromOid(INT8OID, -1);
                        coldef->colname = "max_value";
                        value[i - 1] = Int64GetDatumFast(new.max_value);
                        break;
                  case SEQ_COL_MINVALUE:
                        coldef->typename = makeTypeNameFromOid(INT8OID, -1);
                        coldef->colname = "min_value";
                        value[i - 1] = Int64GetDatumFast(new.min_value);
                        break;
                  case SEQ_COL_CACHE:
                        coldef->typename = makeTypeNameFromOid(INT8OID, -1);
                        coldef->colname = "cache_value";
                        value[i - 1] = Int64GetDatumFast(new.cache_value);
                        break;
                  case SEQ_COL_LOG:
                        coldef->typename = makeTypeNameFromOid(INT8OID, -1);
                        coldef->colname = "log_cnt";
                        value[i - 1] = Int64GetDatum((int64) 1);
                        break;
                  case SEQ_COL_CYCLE:
                        coldef->typename = makeTypeNameFromOid(BOOLOID, -1);
                        coldef->colname = "is_cycled";
                        value[i - 1] = BoolGetDatum(new.is_cycled);
                        break;
                  case SEQ_COL_CALLED:
                        coldef->typename = makeTypeNameFromOid(BOOLOID, -1);
                        coldef->colname = "is_called";
                        value[i - 1] = BoolGetDatum(false);
                        break;
            }
            stmt->tableElts = lappend(stmt->tableElts, coldef);
      }

      stmt->relation = seq->sequence;
      stmt->inhRelations = NIL;
      stmt->constraints = NIL;
      stmt->options = list_make1(defWithOids(false));
      stmt->oncommit = ONCOMMIT_NOOP;
      stmt->tablespacename = NULL;

      seqoid = DefineRelation(stmt, RELKIND_SEQUENCE);

      rel = heap_open(seqoid, AccessExclusiveLock);
      tupDesc = RelationGetDescr(rel);

      /* Initialize first page of relation with special magic number */

      buf = ReadBuffer(rel, P_NEW);
      Assert(BufferGetBlockNumber(buf) == 0);

      page = BufferGetPage(buf);

      PageInit(page, BufferGetPageSize(buf), sizeof(sequence_magic));
      sm = (sequence_magic *) PageGetSpecialPointer(page);
      sm->magic = SEQ_MAGIC;

      /* hack: ensure heap_insert will insert on the just-created page */
      rel->rd_targblock = 0;

      /* Now form & insert sequence tuple */
      tuple = heap_form_tuple(tupDesc, value, null);
      simple_heap_insert(rel, tuple);

      Assert(ItemPointerGetOffsetNumber(&(tuple->t_self)) == FirstOffsetNumber);

      /*
       * Two special hacks here:
       *
       * 1. Since VACUUM does not process sequences, we have to force the tuple
       * to have xmin = FrozenTransactionId now.      Otherwise it would become
       * invisible to SELECTs after 2G transactions.  It is okay to do this
       * because if the current transaction aborts, no other xact will ever
       * examine the sequence tuple anyway.
       *
       * 2. Even though heap_insert emitted a WAL log record, we have to emit an
       * XLOG_SEQ_LOG record too, since (a) the heap_insert record will not have
       * the right xmin, and (b) REDO of the heap_insert record would re-init
       * page and sequence magic number would be lost.  This means two log
       * records instead of one :-(
       */
      LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);

      START_CRIT_SECTION();

      {
            /*
             * Note that the "tuple" structure is still just a local tuple record
             * created by heap_form_tuple; its t_data pointer doesn't point at the
             * disk buffer.  To scribble on the disk buffer we need to fetch the
             * item pointer.  But do the same to the local tuple, since that will
             * be the source for the WAL log record, below.
             */
            ItemId            itemId;
            Item        item;

            itemId = PageGetItemId((Page) page, FirstOffsetNumber);
            item = PageGetItem((Page) page, itemId);

            HeapTupleHeaderSetXmin((HeapTupleHeader) item, FrozenTransactionId);
            ((HeapTupleHeader) item)->t_infomask |= HEAP_XMIN_COMMITTED;

            HeapTupleHeaderSetXmin(tuple->t_data, FrozenTransactionId);
            tuple->t_data->t_infomask |= HEAP_XMIN_COMMITTED;
      }

      MarkBufferDirty(buf);

      /* XLOG stuff */
      if (!rel->rd_istemp)
      {
            xl_seq_rec  xlrec;
            XLogRecPtr  recptr;
            XLogRecData rdata[2];
            Form_pg_sequence newseq = (Form_pg_sequence) GETSTRUCT(tuple);

            /* We do not log first nextval call, so "advance" sequence here */
            /* Note we are scribbling on local tuple, not the disk buffer */
            newseq->is_called = true;
            newseq->log_cnt = 0;

            xlrec.node = rel->rd_node;
            rdata[0].data = (char *) &xlrec;
            rdata[0].len = sizeof(xl_seq_rec);
            rdata[0].buffer = InvalidBuffer;
            rdata[0].next = &(rdata[1]);

            rdata[1].data = (char *) tuple->t_data;
            rdata[1].len = tuple->t_len;
            rdata[1].buffer = InvalidBuffer;
            rdata[1].next = NULL;

            recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG, rdata);

            PageSetLSN(page, recptr);
            PageSetTLI(page, ThisTimeLineID);
      }

      END_CRIT_SECTION();

      UnlockReleaseBuffer(buf);

      /* process OWNED BY if given */
      if (owned_by)
            process_owned_by(rel, owned_by);

      heap_close(rel, NoLock);
}

/*
 * AlterSequence
 *
 * Modify the definition of a sequence relation
 */
void
AlterSequence(AlterSeqStmt *stmt)
{
      Oid               relid;

      /* find sequence */
      relid = RangeVarGetRelid(stmt->sequence, false);

      /* allow ALTER to sequence owner only */
      /* if you change this, see also callers of AlterSequenceInternal! */
      if (!pg_class_ownercheck(relid, GetUserId()))
            aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
                                 stmt->sequence->relname);

      /* do the work */
      AlterSequenceInternal(relid, stmt->options);
}

/*
 * AlterSequenceInternal
 *
 * Same as AlterSequence except that the sequence is specified by OID
 * and we assume the caller already checked permissions.
 */
void
AlterSequenceInternal(Oid relid, List *options)
{
      SeqTable    elm;
      Relation    seqrel;
      Buffer            buf;
      Page        page;
      Form_pg_sequence seq;
      FormData_pg_sequence new;
      List     *owned_by;

      /* open and AccessShareLock sequence */
      init_sequence(relid, &elm, &seqrel);

      /* lock page' buffer and read tuple into new sequence structure */
      seq = read_info(elm, seqrel, &buf);
      page = BufferGetPage(buf);

      /* Copy old values of options into workspace */
      memcpy(&new, seq, sizeof(FormData_pg_sequence));

      /* Check and set new values */
      init_params(options, false, &new, &owned_by);

      /* Clear local cache so that we don't think we have cached numbers */
      /* Note that we do not change the currval() state */
      elm->cached = elm->last;

      /* Now okay to update the on-disk tuple */
      memcpy(seq, &new, sizeof(FormData_pg_sequence));

      START_CRIT_SECTION();

      MarkBufferDirty(buf);

      /* XLOG stuff */
      if (!seqrel->rd_istemp)
      {
            xl_seq_rec  xlrec;
            XLogRecPtr  recptr;
            XLogRecData rdata[2];

            xlrec.node = seqrel->rd_node;
            rdata[0].data = (char *) &xlrec;
            rdata[0].len = sizeof(xl_seq_rec);
            rdata[0].buffer = InvalidBuffer;
            rdata[0].next = &(rdata[1]);

            rdata[1].data = (char *) page + ((PageHeader) page)->pd_upper;
            rdata[1].len = ((PageHeader) page)->pd_special -
                  ((PageHeader) page)->pd_upper;
            rdata[1].buffer = InvalidBuffer;
            rdata[1].next = NULL;

            recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG, rdata);

            PageSetLSN(page, recptr);
            PageSetTLI(page, ThisTimeLineID);
      }

      END_CRIT_SECTION();

      UnlockReleaseBuffer(buf);

      /* process OWNED BY if given */
      if (owned_by)
            process_owned_by(seqrel, owned_by);

      relation_close(seqrel, NoLock);
}


/*
 * Note: nextval with a text argument is no longer exported as a pg_proc
 * entry, but we keep it around to ease porting of C code that may have
 * called the function directly.
 */
Datum
nextval(PG_FUNCTION_ARGS)
{
      text     *seqin = PG_GETARG_TEXT_P(0);
      RangeVar   *sequence;
      Oid               relid;

      sequence = makeRangeVarFromNameList(textToQualifiedNameList(seqin));
      relid = RangeVarGetRelid(sequence, false);

      PG_RETURN_INT64(nextval_internal(relid));
}

Datum
nextval_oid(PG_FUNCTION_ARGS)
{
      Oid               relid = PG_GETARG_OID(0);

      PG_RETURN_INT64(nextval_internal(relid));
}

static int64
nextval_internal(Oid relid)
{
      SeqTable    elm;
      Relation    seqrel;
      Buffer            buf;
      Page        page;
      Form_pg_sequence seq;
      int64       incby,
                        maxv,
                        minv,
                        cache,
                        log,
                        fetch,
                        last;
      int64       result,
                        next,
                        rescnt = 0;
      bool        logit = false;

      /* open and AccessShareLock sequence */
      init_sequence(relid, &elm, &seqrel);

      if (pg_class_aclcheck(elm->relid, GetUserId(), ACL_USAGE) != ACLCHECK_OK &&
            pg_class_aclcheck(elm->relid, GetUserId(), ACL_UPDATE) != ACLCHECK_OK)
            ereport(ERROR,
                        (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                         errmsg("permission denied for sequence %s",
                                    RelationGetRelationName(seqrel))));

      if (elm->last != elm->cached)       /* some numbers were cached */
      {
            Assert(elm->last_valid);
            Assert(elm->increment != 0);
            elm->last += elm->increment;
            relation_close(seqrel, NoLock);
            last_used_seq = elm;
            return elm->last;
      }

      /* lock page' buffer and read tuple */
      seq = read_info(elm, seqrel, &buf);
      page = BufferGetPage(buf);

      last = next = result = seq->last_value;
      incby = seq->increment_by;
      maxv = seq->max_value;
      minv = seq->min_value;
      fetch = cache = seq->cache_value;
      log = seq->log_cnt;

      if (!seq->is_called)
      {
            rescnt++;                     /* last_value if not called */
            fetch--;
            log--;
      }

      /*
       * Decide whether we should emit a WAL log record.    If so, force up the
       * fetch count to grab SEQ_LOG_VALS more values than we actually need to
       * cache.  (These will then be usable without logging.)
       *
       * If this is the first nextval after a checkpoint, we must force a new
       * WAL record to be written anyway, else replay starting from the
       * checkpoint would fail to advance the sequence past the logged values.
       * In this case we may as well fetch extra values.
       */
      if (log < fetch)
      {
            /* forced log to satisfy local demand for values */
            fetch = log = fetch + SEQ_LOG_VALS;
            logit = true;
      }
      else
      {
            XLogRecPtr  redoptr = GetRedoRecPtr();

            if (XLByteLE(PageGetLSN(page), redoptr))
            {
                  /* last update of seq was before checkpoint */
                  fetch = log = fetch + SEQ_LOG_VALS;
                  logit = true;
            }
      }

      while (fetch)                       /* try to fetch cache [+ log ] numbers */
      {
            /*
             * Check MAXVALUE for ascending sequences and MINVALUE for descending
             * sequences
             */
            if (incby > 0)
            {
                  /* ascending sequence */
                  if ((maxv >= 0 && next > maxv - incby) ||
                        (maxv < 0 && next + incby > maxv))
                  {
                        if (rescnt > 0)
                              break;            /* stop fetching */
                        if (!seq->is_cycled)
                        {
                              char        buf[100];

                              snprintf(buf, sizeof(buf), INT64_FORMAT, maxv);
                              ereport(ERROR,
                                      (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                       errmsg("nextval: reached maximum value of sequence \"%s\" (%s)",
                                                  RelationGetRelationName(seqrel), buf)));
                        }
                        next = minv;
                  }
                  else
                        next += incby;
            }
            else
            {
                  /* descending sequence */
                  if ((minv < 0 && next < minv - incby) ||
                        (minv >= 0 && next + incby < minv))
                  {
                        if (rescnt > 0)
                              break;            /* stop fetching */
                        if (!seq->is_cycled)
                        {
                              char        buf[100];

                              snprintf(buf, sizeof(buf), INT64_FORMAT, minv);
                              ereport(ERROR,
                                      (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                       errmsg("nextval: reached minimum value of sequence \"%s\" (%s)",
                                                  RelationGetRelationName(seqrel), buf)));
                        }
                        next = maxv;
                  }
                  else
                        next += incby;
            }
            fetch--;
            if (rescnt < cache)
            {
                  log--;
                  rescnt++;
                  last = next;
                  if (rescnt == 1)  /* if it's first result - */
                        result = next;    /* it's what to return */
            }
      }

      log -= fetch;                       /* adjust for any unfetched numbers */
      Assert(log >= 0);

      /* save info in local cache */
      elm->last = result;                 /* last returned number */
      elm->cached = last;                 /* last fetched number */
      elm->last_valid = true;

      last_used_seq = elm;

      START_CRIT_SECTION();

      MarkBufferDirty(buf);

      /* XLOG stuff */
      if (logit && !seqrel->rd_istemp)
      {
            xl_seq_rec  xlrec;
            XLogRecPtr  recptr;
            XLogRecData rdata[2];

            xlrec.node = seqrel->rd_node;
            rdata[0].data = (char *) &xlrec;
            rdata[0].len = sizeof(xl_seq_rec);
            rdata[0].buffer = InvalidBuffer;
            rdata[0].next = &(rdata[1]);

            /* set values that will be saved in xlog */
            seq->last_value = next;
            seq->is_called = true;
            seq->log_cnt = 0;

            rdata[1].data = (char *) page + ((PageHeader) page)->pd_upper;
            rdata[1].len = ((PageHeader) page)->pd_special -
                  ((PageHeader) page)->pd_upper;
            rdata[1].buffer = InvalidBuffer;
            rdata[1].next = NULL;

            recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG, rdata);

            PageSetLSN(page, recptr);
            PageSetTLI(page, ThisTimeLineID);
      }

      /* update on-disk data */
      seq->last_value = last;       /* last fetched number */
      seq->is_called = true;
      seq->log_cnt = log;                 /* how much is logged */

      END_CRIT_SECTION();

      UnlockReleaseBuffer(buf);

      relation_close(seqrel, NoLock);

      return result;
}

Datum
currval_oid(PG_FUNCTION_ARGS)
{
      Oid               relid = PG_GETARG_OID(0);
      int64       result;
      SeqTable    elm;
      Relation    seqrel;

      /* open and AccessShareLock sequence */
      init_sequence(relid, &elm, &seqrel);

      if (pg_class_aclcheck(elm->relid, GetUserId(), ACL_SELECT) != ACLCHECK_OK &&
            pg_class_aclcheck(elm->relid, GetUserId(), ACL_USAGE) != ACLCHECK_OK)
            ereport(ERROR,
                        (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                         errmsg("permission denied for sequence %s",
                                    RelationGetRelationName(seqrel))));

      if (!elm->last_valid)
            ereport(ERROR,
                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("currval of sequence \"%s\" is not yet defined in this session",
                                    RelationGetRelationName(seqrel))));

      result = elm->last;

      relation_close(seqrel, NoLock);

      PG_RETURN_INT64(result);
}

Datum
lastval(PG_FUNCTION_ARGS)
{
      Relation    seqrel;
      int64       result;

      if (last_used_seq == NULL)
            ereport(ERROR,
                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("lastval is not yet defined in this session")));

      /* Someone may have dropped the sequence since the last nextval() */
      if (!SearchSysCacheExists(RELOID,
                                            ObjectIdGetDatum(last_used_seq->relid),
                                            0, 0, 0))
            ereport(ERROR,
                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("lastval is not yet defined in this session")));

      seqrel = open_share_lock(last_used_seq);

      /* nextval() must have already been called for this sequence */
      Assert(last_used_seq->last_valid);

      if (pg_class_aclcheck(last_used_seq->relid, GetUserId(), ACL_SELECT) != ACLCHECK_OK &&
            pg_class_aclcheck(last_used_seq->relid, GetUserId(), ACL_USAGE) != ACLCHECK_OK)
            ereport(ERROR,
                        (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                         errmsg("permission denied for sequence %s",
                                    RelationGetRelationName(seqrel))));

      result = last_used_seq->last;
      relation_close(seqrel, NoLock);

      PG_RETURN_INT64(result);
}

/*
 * Main internal procedure that handles 2 & 3 arg forms of SETVAL.
 *
 * Note that the 3 arg version (which sets the is_called flag) is
 * only for use in pg_dump, and setting the is_called flag may not
 * work if multiple users are attached to the database and referencing
 * the sequence (unlikely if pg_dump is restoring it).
 *
 * It is necessary to have the 3 arg version so that pg_dump can
 * restore the state of a sequence exactly during data-only restores -
 * it is the only way to clear the is_called flag in an existing
 * sequence.
 */
static void
do_setval(Oid relid, int64 next, bool iscalled)
{
      SeqTable    elm;
      Relation    seqrel;
      Buffer            buf;
      Form_pg_sequence seq;

      /* open and AccessShareLock sequence */
      init_sequence(relid, &elm, &seqrel);

      if (pg_class_aclcheck(elm->relid, GetUserId(), ACL_UPDATE) != ACLCHECK_OK)
            ereport(ERROR,
                        (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                         errmsg("permission denied for sequence %s",
                                    RelationGetRelationName(seqrel))));

      /* lock page' buffer and read tuple */
      seq = read_info(elm, seqrel, &buf);

      if ((next < seq->min_value) || (next > seq->max_value))
      {
            char        bufv[100],
                              bufm[100],
                              bufx[100];

            snprintf(bufv, sizeof(bufv), INT64_FORMAT, next);
            snprintf(bufm, sizeof(bufm), INT64_FORMAT, seq->min_value);
            snprintf(bufx, sizeof(bufx), INT64_FORMAT, seq->max_value);
            ereport(ERROR,
                        (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
                         errmsg("setval: value %s is out of bounds for sequence \"%s\" (%s..%s)",
                                    bufv, RelationGetRelationName(seqrel),
                                    bufm, bufx)));
      }

      /* Set the currval() state only if iscalled = true */
      if (iscalled)
      {
            elm->last = next;       /* last returned number */
            elm->last_valid = true;
      }

      /* In any case, forget any future cached numbers */
      elm->cached = elm->last;

      START_CRIT_SECTION();

      MarkBufferDirty(buf);

      /* XLOG stuff */
      if (!seqrel->rd_istemp)
      {
            xl_seq_rec  xlrec;
            XLogRecPtr  recptr;
            XLogRecData rdata[2];
            Page        page = BufferGetPage(buf);

            xlrec.node = seqrel->rd_node;
            rdata[0].data = (char *) &xlrec;
            rdata[0].len = sizeof(xl_seq_rec);
            rdata[0].buffer = InvalidBuffer;
            rdata[0].next = &(rdata[1]);

            /* set values that will be saved in xlog */
            seq->last_value = next;
            seq->is_called = true;
            seq->log_cnt = 0;

            rdata[1].data = (char *) page + ((PageHeader) page)->pd_upper;
            rdata[1].len = ((PageHeader) page)->pd_special -
                  ((PageHeader) page)->pd_upper;
            rdata[1].buffer = InvalidBuffer;
            rdata[1].next = NULL;

            recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG, rdata);

            PageSetLSN(page, recptr);
            PageSetTLI(page, ThisTimeLineID);
      }

      /* save info in sequence relation */
      seq->last_value = next;       /* last fetched number */
      seq->is_called = iscalled;
      seq->log_cnt = (iscalled) ? 0 : 1;

      END_CRIT_SECTION();

      UnlockReleaseBuffer(buf);

      relation_close(seqrel, NoLock);
}

/*
 * Implement the 2 arg setval procedure.
 * See do_setval for discussion.
 */
Datum
setval_oid(PG_FUNCTION_ARGS)
{
      Oid               relid = PG_GETARG_OID(0);
      int64       next = PG_GETARG_INT64(1);

      do_setval(relid, next, true);

      PG_RETURN_INT64(next);
}

/*
 * Implement the 3 arg setval procedure.
 * See do_setval for discussion.
 */
Datum
setval3_oid(PG_FUNCTION_ARGS)
{
      Oid               relid = PG_GETARG_OID(0);
      int64       next = PG_GETARG_INT64(1);
      bool        iscalled = PG_GETARG_BOOL(2);

      do_setval(relid, next, iscalled);

      PG_RETURN_INT64(next);
}


/*
 * Open the sequence and acquire AccessShareLock if needed
 *
 * If we haven't touched the sequence already in this transaction,
 * we need to acquire AccessShareLock.    We arrange for the lock to
 * be owned by the top transaction, so that we don't need to do it
 * more than once per xact.
 */
static Relation
open_share_lock(SeqTable seq)
{
      LocalTransactionId thislxid = MyProc->lxid;

      /* Get the lock if not already held in this xact */
      if (seq->lxid != thislxid)
      {
            ResourceOwner currentOwner;

            currentOwner = CurrentResourceOwner;
            PG_TRY();
            {
                  CurrentResourceOwner = TopTransactionResourceOwner;
                  LockRelationOid(seq->relid, AccessShareLock);
            }
            PG_CATCH();
            {
                  /* Ensure CurrentResourceOwner is restored on error */
                  CurrentResourceOwner = currentOwner;
                  PG_RE_THROW();
            }
            PG_END_TRY();
            CurrentResourceOwner = currentOwner;

            /* Flag that we have a lock in the current xact */
            seq->lxid = thislxid;
      }

      /* We now know we have AccessShareLock, and can safely open the rel */
      return relation_open(seq->relid, NoLock);
}

/*
 * Given a relation OID, open and lock the sequence.  p_elm and p_rel are
 * output parameters.
 */
static void
init_sequence(Oid relid, SeqTable *p_elm, Relation *p_rel)
{
      SeqTable    elm;
      Relation    seqrel;

      /* Look to see if we already have a seqtable entry for relation */
      for (elm = seqtab; elm != NULL; elm = elm->next)
      {
            if (elm->relid == relid)
                  break;
      }

      /*
       * Allocate new seqtable entry if we didn't find one.
       *
       * NOTE: seqtable entries remain in the list for the life of a backend. If
       * the sequence itself is deleted then the entry becomes wasted memory,
       * but it's small enough that this should not matter.
       */
      if (elm == NULL)
      {
            /*
             * Time to make a new seqtable entry.  These entries live as long as
             * the backend does, so we use plain malloc for them.
             */
            elm = (SeqTable) malloc(sizeof(SeqTableData));
            if (elm == NULL)
                  ereport(ERROR,
                              (errcode(ERRCODE_OUT_OF_MEMORY),
                               errmsg("out of memory")));
            elm->relid = relid;
            elm->lxid = InvalidLocalTransactionId;
            elm->last_valid = false;
            elm->last = elm->cached = elm->increment = 0;
            elm->next = seqtab;
            seqtab = elm;
      }

      /*
       * Open the sequence relation.
       */
      seqrel = open_share_lock(elm);

      if (seqrel->rd_rel->relkind != RELKIND_SEQUENCE)
            ereport(ERROR,
                        (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                         errmsg("\"%s\" is not a sequence",
                                    RelationGetRelationName(seqrel))));

      *p_elm = elm;
      *p_rel = seqrel;
}


/* Given an opened relation, lock the page buffer and find the tuple */
static Form_pg_sequence
read_info(SeqTable elm, Relation rel, Buffer *buf)
{
      Page        page;
      ItemId            lp;
      HeapTupleData tuple;
      sequence_magic *sm;
      Form_pg_sequence seq;

      *buf = ReadBuffer(rel, 0);
      LockBuffer(*buf, BUFFER_LOCK_EXCLUSIVE);

      page = BufferGetPage(*buf);
      sm = (sequence_magic *) PageGetSpecialPointer(page);

      if (sm->magic != SEQ_MAGIC)
            elog(ERROR, "bad magic number in sequence \"%s\": %08X",
                   RelationGetRelationName(rel), sm->magic);

      lp = PageGetItemId(page, FirstOffsetNumber);
      Assert(ItemIdIsNormal(lp));
      tuple.t_data = (HeapTupleHeader) PageGetItem(page, lp);

      seq = (Form_pg_sequence) GETSTRUCT(&tuple);

      /* this is a handy place to update our copy of the increment */
      elm->increment = seq->increment_by;

      return seq;
}

/*
 * init_params: process the options list of CREATE or ALTER SEQUENCE,
 * and store the values into appropriate fields of *new.  Also set
 * *owned_by to any OWNED BY option, or to NIL if there is none.
 *
 * If isInit is true, fill any unspecified options with default values;
 * otherwise, do not change existing options that aren't explicitly overridden.
 */
static void
init_params(List *options, bool isInit,
                  Form_pg_sequence new, List **owned_by)
{
      DefElem    *start_value = NULL;
      DefElem    *restart_value = NULL;
      DefElem    *increment_by = NULL;
      DefElem    *max_value = NULL;
      DefElem    *min_value = NULL;
      DefElem    *cache_value = NULL;
      DefElem    *is_cycled = NULL;
      ListCell   *option;

      *owned_by = NIL;

      foreach(option, options)
      {
            DefElem    *defel = (DefElem *) lfirst(option);

            if (strcmp(defel->defname, "increment") == 0)
            {
                  if (increment_by)
                        ereport(ERROR,
                                    (errcode(ERRCODE_SYNTAX_ERROR),
                                     errmsg("conflicting or redundant options")));
                  increment_by = defel;
            }
            else if (strcmp(defel->defname, "start") == 0)
            {
                  if (start_value)
                        ereport(ERROR,
                                    (errcode(ERRCODE_SYNTAX_ERROR),
                                     errmsg("conflicting or redundant options")));
                  start_value = defel;
            }
            else if (strcmp(defel->defname, "restart") == 0)
            {
                  if (restart_value)
                        ereport(ERROR,
                                    (errcode(ERRCODE_SYNTAX_ERROR),
                                     errmsg("conflicting or redundant options")));
                  restart_value = defel;
            }
            else if (strcmp(defel->defname, "maxvalue") == 0)
            {
                  if (max_value)
                        ereport(ERROR,
                                    (errcode(ERRCODE_SYNTAX_ERROR),
                                     errmsg("conflicting or redundant options")));
                  max_value = defel;
            }
            else if (strcmp(defel->defname, "minvalue") == 0)
            {
                  if (min_value)
                        ereport(ERROR,
                                    (errcode(ERRCODE_SYNTAX_ERROR),
                                     errmsg("conflicting or redundant options")));
                  min_value = defel;
            }
            else if (strcmp(defel->defname, "cache") == 0)
            {
                  if (cache_value)
                        ereport(ERROR,
                                    (errcode(ERRCODE_SYNTAX_ERROR),
                                     errmsg("conflicting or redundant options")));
                  cache_value = defel;
            }
            else if (strcmp(defel->defname, "cycle") == 0)
            {
                  if (is_cycled)
                        ereport(ERROR,
                                    (errcode(ERRCODE_SYNTAX_ERROR),
                                     errmsg("conflicting or redundant options")));
                  is_cycled = defel;
            }
            else if (strcmp(defel->defname, "owned_by") == 0)
            {
                  if (*owned_by)
                        ereport(ERROR,
                                    (errcode(ERRCODE_SYNTAX_ERROR),
                                     errmsg("conflicting or redundant options")));
                  *owned_by = defGetQualifiedName(defel);
            }
            else
                  elog(ERROR, "option \"%s\" not recognized",
                         defel->defname);
      }

      /* INCREMENT BY */
      if (increment_by != NULL)
      {
            new->increment_by = defGetInt64(increment_by);
            if (new->increment_by == 0)
                  ereport(ERROR,
                              (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                               errmsg("INCREMENT must not be zero")));
      }
      else if (isInit)
            new->increment_by = 1;

      /* CYCLE */
      if (is_cycled != NULL)
      {
            new->is_cycled = intVal(is_cycled->arg);
            Assert(new->is_cycled == false || new->is_cycled == true);
      }
      else if (isInit)
            new->is_cycled = false;

      /* MAXVALUE (null arg means NO MAXVALUE) */
      if (max_value != NULL && max_value->arg)
            new->max_value = defGetInt64(max_value);
      else if (isInit || max_value != NULL)
      {
            if (new->increment_by > 0)
                  new->max_value = SEQ_MAXVALUE;            /* ascending seq */
            else
                  new->max_value = -1;    /* descending seq */
      }

      /* MINVALUE (null arg means NO MINVALUE) */
      if (min_value != NULL && min_value->arg)
            new->min_value = defGetInt64(min_value);
      else if (isInit || min_value != NULL)
      {
            if (new->increment_by > 0)
                  new->min_value = 1; /* ascending seq */
            else
                  new->min_value = SEQ_MINVALUE;            /* descending seq */
      }

      /* crosscheck min/max */
      if (new->min_value >= new->max_value)
      {
            char        bufm[100],
                              bufx[100];

            snprintf(bufm, sizeof(bufm), INT64_FORMAT, new->min_value);
            snprintf(bufx, sizeof(bufx), INT64_FORMAT, new->max_value);
            ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("MINVALUE (%s) must be less than MAXVALUE (%s)",
                                    bufm, bufx)));
      }

      /* START WITH */
      if (start_value != NULL)
            new->start_value = defGetInt64(start_value);
      else if (isInit)
      {
            if (new->increment_by > 0)
                  new->start_value = new->min_value;  /* ascending seq */
            else
                  new->start_value = new->max_value;  /* descending seq */
      }

      /* crosscheck START */
      if (new->start_value < new->min_value)
      {
            char        bufs[100],
                              bufm[100];

            snprintf(bufs, sizeof(bufs), INT64_FORMAT, new->start_value);
            snprintf(bufm, sizeof(bufm), INT64_FORMAT, new->min_value);
            ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("START value (%s) cannot be less than MINVALUE (%s)",
                                    bufs, bufm)));
      }
      if (new->start_value > new->max_value)
      {
            char        bufs[100],
                              bufm[100];

            snprintf(bufs, sizeof(bufs), INT64_FORMAT, new->start_value);
            snprintf(bufm, sizeof(bufm), INT64_FORMAT, new->max_value);
            ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                    errmsg("START value (%s) cannot be greater than MAXVALUE (%s)",
                               bufs, bufm)));
      }

      /* RESTART [WITH] */
      if (restart_value != NULL)
      {
            if (restart_value->arg != NULL)
                  new->last_value = defGetInt64(restart_value);
            else
                  new->last_value = new->start_value;
            new->is_called = false;
            new->log_cnt = 1;
      }
      else if (isInit)
      {
            new->last_value = new->start_value;
            new->is_called = false;
            new->log_cnt = 1;
      }

      /* crosscheck RESTART (or current value, if changing MIN/MAX) */
      if (new->last_value < new->min_value)
      {
            char        bufs[100],
                              bufm[100];

            snprintf(bufs, sizeof(bufs), INT64_FORMAT, new->last_value);
            snprintf(bufm, sizeof(bufm), INT64_FORMAT, new->min_value);
            ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("RESTART value (%s) cannot be less than MINVALUE (%s)",
                                    bufs, bufm)));
      }
      if (new->last_value > new->max_value)
      {
            char        bufs[100],
                              bufm[100];

            snprintf(bufs, sizeof(bufs), INT64_FORMAT, new->last_value);
            snprintf(bufm, sizeof(bufm), INT64_FORMAT, new->max_value);
            ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                    errmsg("RESTART value (%s) cannot be greater than MAXVALUE (%s)",
                               bufs, bufm)));
      }

      /* CACHE */
      if (cache_value != NULL)
      {
            new->cache_value = defGetInt64(cache_value);
            if (new->cache_value <= 0)
            {
                  char        buf[100];

                  snprintf(buf, sizeof(buf), INT64_FORMAT, new->cache_value);
                  ereport(ERROR,
                              (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                               errmsg("CACHE (%s) must be greater than zero",
                                          buf)));
            }
      }
      else if (isInit)
            new->cache_value = 1;
}

/*
 * Process an OWNED BY option for CREATE/ALTER SEQUENCE
 *
 * Ownership permissions on the sequence are already checked,
 * but if we are establishing a new owned-by dependency, we must
 * enforce that the referenced table has the same owner and namespace
 * as the sequence.
 */
static void
process_owned_by(Relation seqrel, List *owned_by)
{
      int               nnames;
      Relation    tablerel;
      AttrNumber  attnum;

      nnames = list_length(owned_by);
      Assert(nnames > 0);
      if (nnames == 1)
      {
            /* Must be OWNED BY NONE */
            if (strcmp(strVal(linitial(owned_by)), "none") != 0)
                  ereport(ERROR,
                              (errcode(ERRCODE_SYNTAX_ERROR),
                               errmsg("invalid OWNED BY option"),
                        errhint("Specify OWNED BY table.column or OWNED BY NONE.")));
            tablerel = NULL;
            attnum = 0;
      }
      else
      {
            List     *relname;
            char     *attrname;
            RangeVar   *rel;

            /* Separate relname and attr name */
            relname = list_truncate(list_copy(owned_by), nnames - 1);
            attrname = strVal(lfirst(list_tail(owned_by)));

            /* Open and lock rel to ensure it won't go away meanwhile */
            rel = makeRangeVarFromNameList(relname);
            tablerel = relation_openrv(rel, AccessShareLock);

            /* Must be a regular table */
            if (tablerel->rd_rel->relkind != RELKIND_RELATION)
                  ereport(ERROR,
                              (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                               errmsg("referenced relation \"%s\" is not a table",
                                          RelationGetRelationName(tablerel))));

            /* We insist on same owner and schema */
            if (seqrel->rd_rel->relowner != tablerel->rd_rel->relowner)
                  ereport(ERROR,
                              (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                               errmsg("sequence must have same owner as table it is linked to")));
            if (RelationGetNamespace(seqrel) != RelationGetNamespace(tablerel))
                  ereport(ERROR,
                              (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                               errmsg("sequence must be in same schema as table it is linked to")));

            /* Now, fetch the attribute number from the system cache */
            attnum = get_attnum(RelationGetRelid(tablerel), attrname);
            if (attnum == InvalidAttrNumber)
                  ereport(ERROR,
                              (errcode(ERRCODE_UNDEFINED_COLUMN),
                               errmsg("column \"%s\" of relation \"%s\" does not exist",
                                          attrname, RelationGetRelationName(tablerel))));
      }

      /*
       * OK, we are ready to update pg_depend.  First remove any existing AUTO
       * dependencies for the sequence, then optionally add a new one.
       */
      markSequenceUnowned(RelationGetRelid(seqrel));

      if (tablerel)
      {
            ObjectAddress refobject,
                              depobject;

            refobject.classId = RelationRelationId;
            refobject.objectId = RelationGetRelid(tablerel);
            refobject.objectSubId = attnum;
            depobject.classId = RelationRelationId;
            depobject.objectId = RelationGetRelid(seqrel);
            depobject.objectSubId = 0;
            recordDependencyOn(&depobject, &refobject, DEPENDENCY_AUTO);
      }

      /* Done, but hold lock until commit */
      if (tablerel)
            relation_close(tablerel, NoLock);
}


void
seq_redo(XLogRecPtr lsn, XLogRecord *record)
{
      uint8       info = record->xl_info & ~XLR_INFO_MASK;
      Buffer            buffer;
      Page        page;
      char     *item;
      Size        itemsz;
      xl_seq_rec *xlrec = (xl_seq_rec *) XLogRecGetData(record);
      sequence_magic *sm;

      /* Backup blocks are not used in seq records */
      Assert(!(record->xl_info & XLR_BKP_BLOCK_MASK));

      if (info != XLOG_SEQ_LOG)
            elog(PANIC, "seq_redo: unknown op code %u", info);

      buffer = XLogReadBuffer(xlrec->node, 0, true);
      Assert(BufferIsValid(buffer));
      page = (Page) BufferGetPage(buffer);

      /* Always reinit the page and reinstall the magic number */
      /* See comments in DefineSequence */
      PageInit((Page) page, BufferGetPageSize(buffer), sizeof(sequence_magic));
      sm = (sequence_magic *) PageGetSpecialPointer(page);
      sm->magic = SEQ_MAGIC;

      item = (char *) xlrec + sizeof(xl_seq_rec);
      itemsz = record->xl_len - sizeof(xl_seq_rec);
      itemsz = MAXALIGN(itemsz);
      if (PageAddItem(page, (Item) item, itemsz,
                              FirstOffsetNumber, false, false) == InvalidOffsetNumber)
            elog(PANIC, "seq_redo: failed to add item to page");

      PageSetLSN(page, lsn);
      PageSetTLI(page, ThisTimeLineID);
      MarkBufferDirty(buffer);
      UnlockReleaseBuffer(buffer);
}

void
seq_desc(StringInfo buf, uint8 xl_info, char *rec)
{
      uint8       info = xl_info & ~XLR_INFO_MASK;
      xl_seq_rec *xlrec = (xl_seq_rec *) rec;

      if (info == XLOG_SEQ_LOG)
            appendStringInfo(buf, "log: ");
      else
      {
            appendStringInfo(buf, "UNKNOWN");
            return;
      }

      appendStringInfo(buf, "rel %u/%u/%u",
                     xlrec->node.spcNode, xlrec->node.dbNode, xlrec->node.relNode);
}

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