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Sourcecode: postgresql-8.4 version File versions

initsplan.c

/*-------------------------------------------------------------------------
 *
 * initsplan.c
 *      Target list, qualification, joininfo initialization routines
 *
 * 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 "catalog/pg_operator.h"
#include "catalog/pg_type.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/joininfo.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/placeholder.h"
#include "optimizer/planmain.h"
#include "optimizer/prep.h"
#include "optimizer/restrictinfo.h"
#include "optimizer/var.h"
#include "parser/parse_expr.h"
#include "parser/parse_oper.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"


/* These parameters are set by GUC */
int               from_collapse_limit;
int               join_collapse_limit;


static List *deconstruct_recurse(PlannerInfo *root, Node *jtnode,
                              bool below_outer_join,
                              Relids *qualscope, Relids *inner_join_rels);
static SpecialJoinInfo *make_outerjoininfo(PlannerInfo *root,
                           Relids left_rels, Relids right_rels,
                           Relids inner_join_rels,
                           JoinType jointype, List *clause);
static void distribute_qual_to_rels(PlannerInfo *root, Node *clause,
                                    bool is_deduced,
                                    bool below_outer_join,
                                    JoinType jointype,
                                    Relids qualscope,
                                    Relids ojscope,
                                    Relids outerjoin_nonnullable);
static bool check_outerjoin_delay(PlannerInfo *root, Relids *relids_p,
                                bool is_pushed_down);
static bool check_redundant_nullability_qual(PlannerInfo *root, Node *clause);
static void check_mergejoinable(RestrictInfo *restrictinfo);
static void check_hashjoinable(RestrictInfo *restrictinfo);


/*****************************************************************************
 *
 *     JOIN TREES
 *
 *****************************************************************************/

/*
 * add_base_rels_to_query
 *
 *      Scan the query's jointree and create baserel RelOptInfos for all
 *      the base relations (ie, table, subquery, and function RTEs)
 *      appearing in the jointree.
 *
 * The initial invocation must pass root->parse->jointree as the value of
 * jtnode.  Internally, the function recurses through the jointree.
 *
 * At the end of this process, there should be one baserel RelOptInfo for
 * every non-join RTE that is used in the query.  Therefore, this routine
 * is the only place that should call build_simple_rel with reloptkind
 * RELOPT_BASEREL.      (Note: build_simple_rel recurses internally to build
 * "other rel" RelOptInfos for the members of any appendrels we find here.)
 */
void
add_base_rels_to_query(PlannerInfo *root, Node *jtnode)
{
      if (jtnode == NULL)
            return;
      if (IsA(jtnode, RangeTblRef))
      {
            int               varno = ((RangeTblRef *) jtnode)->rtindex;

            (void) build_simple_rel(root, varno, RELOPT_BASEREL);
      }
      else if (IsA(jtnode, FromExpr))
      {
            FromExpr   *f = (FromExpr *) jtnode;
            ListCell   *l;

            foreach(l, f->fromlist)
                  add_base_rels_to_query(root, lfirst(l));
      }
      else if (IsA(jtnode, JoinExpr))
      {
            JoinExpr   *j = (JoinExpr *) jtnode;

            add_base_rels_to_query(root, j->larg);
            add_base_rels_to_query(root, j->rarg);
      }
      else
            elog(ERROR, "unrecognized node type: %d",
                   (int) nodeTag(jtnode));
}


/*****************************************************************************
 *
 *     TARGET LISTS
 *
 *****************************************************************************/

/*
 * build_base_rel_tlists
 *      Add targetlist entries for each var needed in the query's final tlist
 *      to the appropriate base relations.
 *
 * We mark such vars as needed by "relation 0" to ensure that they will
 * propagate up through all join plan steps.
 */
void
build_base_rel_tlists(PlannerInfo *root, List *final_tlist)
{
      List     *tlist_vars = pull_var_clause((Node *) final_tlist, true);

      if (tlist_vars != NIL)
      {
            add_vars_to_targetlist(root, tlist_vars, bms_make_singleton(0));
            list_free(tlist_vars);
      }
}

/*
 * add_vars_to_targetlist
 *      For each variable appearing in the list, add it to the owning
 *      relation's targetlist if not already present, and mark the variable
 *      as being needed for the indicated join (or for final output if
 *      where_needed includes "relation 0").
 *
 *      The list may also contain PlaceHolderVars.  These don't necessarily
 *      have a single owning relation; we keep their attr_needed info in
 *      root->placeholder_list instead.
 */
void
add_vars_to_targetlist(PlannerInfo *root, List *vars, Relids where_needed)
{
      ListCell   *temp;

      Assert(!bms_is_empty(where_needed));

      foreach(temp, vars)
      {
            Node     *node = (Node *) lfirst(temp);

            if (IsA(node, Var))
            {
                  Var            *var = (Var *) node;
                  RelOptInfo *rel = find_base_rel(root, var->varno);
                  int               attno = var->varattno;

                  Assert(attno >= rel->min_attr && attno <= rel->max_attr);
                  attno -= rel->min_attr;
                  if (rel->attr_needed[attno] == NULL)
                  {
                        /* Variable not yet requested, so add to reltargetlist */
                        /* XXX is copyObject necessary here? */
                        rel->reltargetlist = lappend(rel->reltargetlist,
                                                                   copyObject(var));
                  }
                  rel->attr_needed[attno] = bms_add_members(rel->attr_needed[attno],
                                                                                where_needed);
            }
            else if (IsA(node, PlaceHolderVar))
            {
                  PlaceHolderVar *phv = (PlaceHolderVar *) node;
                  PlaceHolderInfo *phinfo = find_placeholder_info(root, phv);

                  phinfo->ph_needed = bms_add_members(phinfo->ph_needed,
                                                                        where_needed);
            }
            else
                  elog(ERROR, "unrecognized node type: %d", (int) nodeTag(node));
      }
}


/*****************************************************************************
 *
 *      JOIN TREE PROCESSING
 *
 *****************************************************************************/

/*
 * deconstruct_jointree
 *      Recursively scan the query's join tree for WHERE and JOIN/ON qual
 *      clauses, and add these to the appropriate restrictinfo and joininfo
 *      lists belonging to base RelOptInfos.    Also, add SpecialJoinInfo nodes
 *      to root->join_info_list for any outer joins appearing in the query tree.
 *      Return a "joinlist" data structure showing the join order decisions
 *      that need to be made by make_one_rel().
 *
 * The "joinlist" result is a list of items that are either RangeTblRef
 * jointree nodes or sub-joinlists.  All the items at the same level of
 * joinlist must be joined in an order to be determined by make_one_rel()
 * (note that legal orders may be constrained by SpecialJoinInfo nodes).
 * A sub-joinlist represents a subproblem to be planned separately. Currently
 * sub-joinlists arise only from FULL OUTER JOIN or when collapsing of
 * subproblems is stopped by join_collapse_limit or from_collapse_limit.
 *
 * NOTE: when dealing with inner joins, it is appropriate to let a qual clause
 * be evaluated at the lowest level where all the variables it mentions are
 * available.  However, we cannot push a qual down into the nullable side(s)
 * of an outer join since the qual might eliminate matching rows and cause a
 * NULL row to be incorrectly emitted by the join.    Therefore, we artificially
 * OR the minimum-relids of such an outer join into the required_relids of
 * clauses appearing above it.      This forces those clauses to be delayed until
 * application of the outer join (or maybe even higher in the join tree).
 */
List *
deconstruct_jointree(PlannerInfo *root)
{
      Relids            qualscope;
      Relids            inner_join_rels;

      /* Start recursion at top of jointree */
      Assert(root->parse->jointree != NULL &&
               IsA(root->parse->jointree, FromExpr));

      return deconstruct_recurse(root, (Node *) root->parse->jointree, false,
                                             &qualscope, &inner_join_rels);
}

/*
 * deconstruct_recurse
 *      One recursion level of deconstruct_jointree processing.
 *
 * Inputs:
 *    jtnode is the jointree node to examine
 *    below_outer_join is TRUE if this node is within the nullable side of a
 *          higher-level outer join
 * Outputs:
 *    *qualscope gets the set of base Relids syntactically included in this
 *          jointree node (do not modify or free this, as it may also be pointed
 *          to by RestrictInfo and SpecialJoinInfo nodes)
 *    *inner_join_rels gets the set of base Relids syntactically included in
 *          inner joins appearing at or below this jointree node (do not modify
 *          or free this, either)
 *    Return value is the appropriate joinlist for this jointree node
 *
 * In addition, entries will be added to root->join_info_list for outer joins.
 */
static List *
deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
                              Relids *qualscope, Relids *inner_join_rels)
{
      List     *joinlist;

      if (jtnode == NULL)
      {
            *qualscope = NULL;
            *inner_join_rels = NULL;
            return NIL;
      }
      if (IsA(jtnode, RangeTblRef))
      {
            int               varno = ((RangeTblRef *) jtnode)->rtindex;

            /* No quals to deal with, just return correct result */
            *qualscope = bms_make_singleton(varno);
            /* A single baserel does not create an inner join */
            *inner_join_rels = NULL;
            joinlist = list_make1(jtnode);
      }
      else if (IsA(jtnode, FromExpr))
      {
            FromExpr   *f = (FromExpr *) jtnode;
            int               remaining;
            ListCell   *l;

            /*
             * First, recurse to handle child joins.  We collapse subproblems into
             * a single joinlist whenever the resulting joinlist wouldn't exceed
             * from_collapse_limit members.  Also, always collapse one-element
             * subproblems, since that won't lengthen the joinlist anyway.
             */
            *qualscope = NULL;
            *inner_join_rels = NULL;
            joinlist = NIL;
            remaining = list_length(f->fromlist);
            foreach(l, f->fromlist)
            {
                  Relids            sub_qualscope;
                  List     *sub_joinlist;
                  int               sub_members;

                  sub_joinlist = deconstruct_recurse(root, lfirst(l),
                                                                     below_outer_join,
                                                                     &sub_qualscope,
                                                                     inner_join_rels);
                  *qualscope = bms_add_members(*qualscope, sub_qualscope);
                  sub_members = list_length(sub_joinlist);
                  remaining--;
                  if (sub_members <= 1 ||
                        list_length(joinlist) + sub_members + remaining <= from_collapse_limit)
                        joinlist = list_concat(joinlist, sub_joinlist);
                  else
                        joinlist = lappend(joinlist, sub_joinlist);
            }

            /*
             * A FROM with more than one list element is an inner join subsuming
             * all below it, so we should report inner_join_rels = qualscope. If
             * there was exactly one element, we should (and already did) report
             * whatever its inner_join_rels were.  If there were no elements (is
             * that possible?) the initialization before the loop fixed it.
             */
            if (list_length(f->fromlist) > 1)
                  *inner_join_rels = *qualscope;

            /*
             * Now process the top-level quals.
             */
            foreach(l, (List *) f->quals)
            {
                  Node   *qual = (Node *) lfirst(l);

                  distribute_qual_to_rels(root, qual,
                                                      false, below_outer_join, JOIN_INNER,
                                                      *qualscope, NULL, NULL);
            }
      }
      else if (IsA(jtnode, JoinExpr))
      {
            JoinExpr   *j = (JoinExpr *) jtnode;
            Relids            leftids,
                              rightids,
                              left_inners,
                              right_inners,
                              nonnullable_rels,
                              ojscope;
            List     *leftjoinlist,
                           *rightjoinlist;
            SpecialJoinInfo *sjinfo;
            ListCell   *l;

            /*
             * Order of operations here is subtle and critical.  First we recurse
             * to handle sub-JOINs.  Their join quals will be placed without
             * regard for whether this level is an outer join, which is correct.
             * Then we place our own join quals, which are restricted by lower
             * outer joins in any case, and are forced to this level if this is an
             * outer join and they mention the outer side.  Finally, if this is an
             * outer join, we create a join_info_list entry for the join.  This
             * will prevent quals above us in the join tree that use those rels
             * from being pushed down below this level.  (It's okay for upper
             * quals to be pushed down to the outer side, however.)
             */
            switch (j->jointype)
            {
                  case JOIN_INNER:
                        leftjoinlist = deconstruct_recurse(root, j->larg,
                                                                           below_outer_join,
                                                                           &leftids, &left_inners);
                        rightjoinlist = deconstruct_recurse(root, j->rarg,
                                                                              below_outer_join,
                                                                              &rightids, &right_inners);
                        *qualscope = bms_union(leftids, rightids);
                        *inner_join_rels = *qualscope;
                        /* Inner join adds no restrictions for quals */
                        nonnullable_rels = NULL;
                        break;
                  case JOIN_LEFT:
                  case JOIN_ANTI:
                        leftjoinlist = deconstruct_recurse(root, j->larg,
                                                                           below_outer_join,
                                                                           &leftids, &left_inners);
                        rightjoinlist = deconstruct_recurse(root, j->rarg,
                                                                              true,
                                                                              &rightids, &right_inners);
                        *qualscope = bms_union(leftids, rightids);
                        *inner_join_rels = bms_union(left_inners, right_inners);
                        nonnullable_rels = leftids;
                        break;
                  case JOIN_SEMI:
                        leftjoinlist = deconstruct_recurse(root, j->larg,
                                                                           below_outer_join,
                                                                           &leftids, &left_inners);
                        rightjoinlist = deconstruct_recurse(root, j->rarg,
                                                                              below_outer_join,
                                                                              &rightids, &right_inners);
                        *qualscope = bms_union(leftids, rightids);
                        *inner_join_rels = bms_union(left_inners, right_inners);
                        /* Semi join adds no restrictions for quals */
                        nonnullable_rels = NULL;
                        break;
                  case JOIN_FULL:
                        leftjoinlist = deconstruct_recurse(root, j->larg,
                                                                           true,
                                                                           &leftids, &left_inners);
                        rightjoinlist = deconstruct_recurse(root, j->rarg,
                                                                              true,
                                                                              &rightids, &right_inners);
                        *qualscope = bms_union(leftids, rightids);
                        *inner_join_rels = bms_union(left_inners, right_inners);
                        /* each side is both outer and inner */
                        nonnullable_rels = *qualscope;
                        break;
                  default:
                        /* JOIN_RIGHT was eliminated during reduce_outer_joins() */
                        elog(ERROR, "unrecognized join type: %d",
                               (int) j->jointype);
                        nonnullable_rels = NULL;            /* keep compiler quiet */
                        leftjoinlist = rightjoinlist = NIL;
                        break;
            }

            /*
             * For an OJ, form the SpecialJoinInfo now, because we need the OJ's
             * semantic scope (ojscope) to pass to distribute_qual_to_rels.  But
             * we mustn't add it to join_info_list just yet, because we don't want
             * distribute_qual_to_rels to think it is an outer join below us.
             *
             * Semijoins are a bit of a hybrid: we build a SpecialJoinInfo,
             * but we want ojscope = NULL for distribute_qual_to_rels.
             */
            if (j->jointype != JOIN_INNER)
            {
                  sjinfo = make_outerjoininfo(root,
                                                            leftids, rightids,
                                                            *inner_join_rels,
                                                            j->jointype,
                                                            (List *) j->quals);
                  if (j->jointype == JOIN_SEMI)
                        ojscope = NULL;
                  else
                        ojscope = bms_union(sjinfo->min_lefthand,
                                                      sjinfo->min_righthand);
            }
            else
            {
                  sjinfo = NULL;
                  ojscope = NULL;
            }

            /* Process the qual clauses */
            foreach(l, (List *) j->quals)
            {
                  Node   *qual = (Node *) lfirst(l);

                  distribute_qual_to_rels(root, qual,
                                                      false, below_outer_join, j->jointype,
                                                      *qualscope,
                                                      ojscope, nonnullable_rels);
            }

            /* Now we can add the SpecialJoinInfo to join_info_list */
            if (sjinfo)
                  root->join_info_list = lappend(root->join_info_list, sjinfo);

            /*
             * Finally, compute the output joinlist.  We fold subproblems together
             * except at a FULL JOIN or where join_collapse_limit would be
             * exceeded.
             */
            if (j->jointype == JOIN_FULL)
            {
                  /* force the join order exactly at this node */
                  joinlist = list_make1(list_make2(leftjoinlist, rightjoinlist));
            }
            else if (list_length(leftjoinlist) + list_length(rightjoinlist) <=
                         join_collapse_limit)
            {
                  /* OK to combine subproblems */
                  joinlist = list_concat(leftjoinlist, rightjoinlist);
            }
            else
            {
                  /* can't combine, but needn't force join order above here */
                  Node     *leftpart,
                                 *rightpart;

                  /* avoid creating useless 1-element sublists */
                  if (list_length(leftjoinlist) == 1)
                        leftpart = (Node *) linitial(leftjoinlist);
                  else
                        leftpart = (Node *) leftjoinlist;
                  if (list_length(rightjoinlist) == 1)
                        rightpart = (Node *) linitial(rightjoinlist);
                  else
                        rightpart = (Node *) rightjoinlist;
                  joinlist = list_make2(leftpart, rightpart);
            }
      }
      else
      {
            elog(ERROR, "unrecognized node type: %d",
                   (int) nodeTag(jtnode));
            joinlist = NIL;               /* keep compiler quiet */
      }
      return joinlist;
}

/*
 * make_outerjoininfo
 *      Build a SpecialJoinInfo for the current outer join
 *
 * Inputs:
 *    left_rels: the base Relids syntactically on outer side of join
 *    right_rels: the base Relids syntactically on inner side of join
 *    inner_join_rels: base Relids participating in inner joins below this one
 *    jointype: what it says (must always be LEFT, FULL, SEMI, or ANTI)
 *    clause: the outer join's join condition (in implicit-AND format)
 *
 * The node should eventually be appended to root->join_info_list, but we
 * do not do that here.
 *
 * Note: we assume that this function is invoked bottom-up, so that
 * root->join_info_list already contains entries for all outer joins that are
 * syntactically below this one.
 */
static SpecialJoinInfo *
make_outerjoininfo(PlannerInfo *root,
                           Relids left_rels, Relids right_rels,
                           Relids inner_join_rels,
                           JoinType jointype, List *clause)
{
      SpecialJoinInfo *sjinfo = makeNode(SpecialJoinInfo);
      Relids            clause_relids;
      Relids            strict_relids;
      Relids            min_lefthand;
      Relids            min_righthand;
      ListCell   *l;

      /*
       * We should not see RIGHT JOIN here because left/right were switched
       * earlier
       */
      Assert(jointype != JOIN_INNER);
      Assert(jointype != JOIN_RIGHT);

      /*
       * Presently the executor cannot support FOR UPDATE/SHARE marking of rels
       * appearing on the nullable side of an outer join. (It's somewhat unclear
       * what that would mean, anyway: what should we mark when a result row is
       * generated from no element of the nullable relation?)  So, complain if
       * any nullable rel is FOR UPDATE/SHARE.
       *
       * You might be wondering why this test isn't made far upstream in the
       * parser.  It's because the parser hasn't got enough info --- consider
       * FOR UPDATE applied to a view.  Only after rewriting and flattening do
       * we know whether the view contains an outer join.
       */
      foreach(l, root->parse->rowMarks)
      {
            RowMarkClause *rc = (RowMarkClause *) lfirst(l);

            if (bms_is_member(rc->rti, right_rels) ||
                  (jointype == JOIN_FULL && bms_is_member(rc->rti, left_rels)))
                  ereport(ERROR,
                              (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                               errmsg("SELECT FOR UPDATE/SHARE cannot be applied to the nullable side of an outer join")));
      }

      sjinfo->syn_lefthand = left_rels;
      sjinfo->syn_righthand = right_rels;
      sjinfo->jointype = jointype;
      /* this always starts out false */
      sjinfo->delay_upper_joins = false;
      sjinfo->join_quals = clause;

      /* If it's a full join, no need to be very smart */
      if (jointype == JOIN_FULL)
      {
            sjinfo->min_lefthand = bms_copy(left_rels);
            sjinfo->min_righthand = bms_copy(right_rels);
            sjinfo->lhs_strict = false;         /* don't care about this */
            return sjinfo;
      }

      /*
       * Retrieve all relids mentioned within the join clause.
       */
      clause_relids = pull_varnos((Node *) clause);

      /*
       * For which relids is the clause strict, ie, it cannot succeed if the
       * rel's columns are all NULL?
       */
      strict_relids = find_nonnullable_rels((Node *) clause);

      /* Remember whether the clause is strict for any LHS relations */
      sjinfo->lhs_strict = bms_overlap(strict_relids, left_rels);

      /*
       * Required LHS always includes the LHS rels mentioned in the clause. We
       * may have to add more rels based on lower outer joins; see below.
       */
      min_lefthand = bms_intersect(clause_relids, left_rels);

      /*
       * Similarly for required RHS.      But here, we must also include any lower
       * inner joins, to ensure we don't try to commute with any of them.
       */
      min_righthand = bms_int_members(bms_union(clause_relids, inner_join_rels),
                                                      right_rels);

      foreach(l, root->join_info_list)
      {
            SpecialJoinInfo *otherinfo = (SpecialJoinInfo *) lfirst(l);

            /* ignore full joins --- other mechanisms preserve their ordering */
            if (otherinfo->jointype == JOIN_FULL)
                  continue;

            /*
             * For a lower OJ in our LHS, if our join condition uses the lower
             * join's RHS and is not strict for that rel, we must preserve the
             * ordering of the two OJs, so add lower OJ's full syntactic relset to
             * min_lefthand.  (We must use its full syntactic relset, not just its
             * min_lefthand + min_righthand.  This is because there might be other
             * OJs below this one that this one can commute with, but we cannot
             * commute with them if we don't with this one.)  Also, if the
             * current join is an antijoin, we must preserve ordering regardless
             * of strictness.
             *
             * Note: I believe we have to insist on being strict for at least one
             * rel in the lower OJ's min_righthand, not its whole syn_righthand.
             */
            if (bms_overlap(left_rels, otherinfo->syn_righthand))
            {
                  if (bms_overlap(clause_relids, otherinfo->syn_righthand) &&
                        (jointype == JOIN_ANTI ||
                         !bms_overlap(strict_relids, otherinfo->min_righthand)))
                  {
                        min_lefthand = bms_add_members(min_lefthand,
                                                                     otherinfo->syn_lefthand);
                        min_lefthand = bms_add_members(min_lefthand,
                                                                     otherinfo->syn_righthand);
                  }
            }

            /*
             * For a lower OJ in our RHS, if our join condition does not use the
             * lower join's RHS and the lower OJ's join condition is strict, we
             * can interchange the ordering of the two OJs; otherwise we must add
             * lower OJ's full syntactic relset to min_righthand.  Here, we must
             * preserve ordering anyway if the lower OJ is an antijoin.
             *
             * Here, we have to consider that "our join condition" includes any
             * clauses that syntactically appeared above the lower OJ and below
             * ours; those are equivalent to degenerate clauses in our OJ and must
             * be treated as such.  Such clauses obviously can't reference our
             * LHS, and they must be non-strict for the lower OJ's RHS (else
             * reduce_outer_joins would have reduced the lower OJ to a plain
             * join).  Hence the other ways in which we handle clauses within our
             * join condition are not affected by them.  The net effect is
             * therefore sufficiently represented by the delay_upper_joins flag
             * saved for us by check_outerjoin_delay.
             */
            if (bms_overlap(right_rels, otherinfo->syn_righthand))
            {
                  if (bms_overlap(clause_relids, otherinfo->syn_righthand) ||
                        otherinfo->jointype == JOIN_ANTI ||
                        !otherinfo->lhs_strict || otherinfo->delay_upper_joins)
                  {
                        min_righthand = bms_add_members(min_righthand,
                                                                        otherinfo->syn_lefthand);
                        min_righthand = bms_add_members(min_righthand,
                                                                        otherinfo->syn_righthand);
                  }
            }
      }

      /*
       * If we found nothing to put in min_lefthand, punt and make it the full
       * LHS, to avoid having an empty min_lefthand which will confuse later
       * processing. (We don't try to be smart about such cases, just correct.)
       * Likewise for min_righthand.
       */
      if (bms_is_empty(min_lefthand))
            min_lefthand = bms_copy(left_rels);
      if (bms_is_empty(min_righthand))
            min_righthand = bms_copy(right_rels);

      /* Now they'd better be nonempty */
      Assert(!bms_is_empty(min_lefthand));
      Assert(!bms_is_empty(min_righthand));
      /* Shouldn't overlap either */
      Assert(!bms_overlap(min_lefthand, min_righthand));

      sjinfo->min_lefthand = min_lefthand;
      sjinfo->min_righthand = min_righthand;

      return sjinfo;
}


/*****************************************************************************
 *
 *      QUALIFICATIONS
 *
 *****************************************************************************/

/*
 * distribute_qual_to_rels
 *      Add clause information to either the baserestrictinfo or joininfo list
 *      (depending on whether the clause is a join) of each base relation
 *      mentioned in the clause.    A RestrictInfo node is created and added to
 *      the appropriate list for each rel.  Alternatively, if the clause uses a
 *      mergejoinable operator and is not delayed by outer-join rules, enter
 *      the left- and right-side expressions into the query's list of
 *      EquivalenceClasses.
 *
 * 'clause': the qual clause to be distributed
 * 'is_deduced': TRUE if the qual came from implied-equality deduction
 * 'below_outer_join': TRUE if the qual is from a JOIN/ON that is below the
 *          nullable side of a higher-level outer join
 * 'jointype': type of join the qual is from (JOIN_INNER for a WHERE clause)
 * 'qualscope': set of baserels the qual's syntactic scope covers
 * 'ojscope': NULL if not an outer-join qual, else the minimum set of baserels
 *          needed to form this join
 * 'outerjoin_nonnullable': NULL if not an outer-join qual, else the set of
 *          baserels appearing on the outer (nonnullable) side of the join
 *          (for FULL JOIN this includes both sides of the join, and must in fact
 *          equal qualscope)
 *
 * 'qualscope' identifies what level of JOIN the qual came from syntactically.
 * 'ojscope' is needed if we decide to force the qual up to the outer-join
 * level, which will be ojscope not necessarily qualscope.
 *
 * At the time this is called, root->join_info_list must contain entries for
 * all and only those special joins that are syntactically below this qual.
 */
static void
distribute_qual_to_rels(PlannerInfo *root, Node *clause,
                                    bool is_deduced,
                                    bool below_outer_join,
                                    JoinType jointype,
                                    Relids qualscope,
                                    Relids ojscope,
                                    Relids outerjoin_nonnullable)
{
      Relids            relids;
      bool        is_pushed_down;
      bool        outerjoin_delayed;
      bool        pseudoconstant = false;
      bool        maybe_equivalence;
      bool        maybe_outer_join;
      RestrictInfo *restrictinfo;

      /*
       * Retrieve all relids mentioned within the clause.
       */
      relids = pull_varnos(clause);

      /*
       * Cross-check: clause should contain no relids not within its scope.
       * Otherwise the parser messed up.
       */
      if (!bms_is_subset(relids, qualscope))
            elog(ERROR, "JOIN qualification cannot refer to other relations");
      if (ojscope && !bms_is_subset(relids, ojscope))
            elog(ERROR, "JOIN qualification cannot refer to other relations");

      /*
       * If the clause is variable-free, our normal heuristic for pushing it
       * down to just the mentioned rels doesn't work, because there are none.
       *
       * If the clause is an outer-join clause, we must force it to the OJ's
       * semantic level to preserve semantics.
       *
       * Otherwise, when the clause contains volatile functions, we force it to
       * be evaluated at its original syntactic level.  This preserves the
       * expected semantics.
       *
       * When the clause contains no volatile functions either, it is actually a
       * pseudoconstant clause that will not change value during any one
       * execution of the plan, and hence can be used as a one-time qual in a
       * gating Result plan node.  We put such a clause into the regular
       * RestrictInfo lists for the moment, but eventually createplan.c will
       * pull it out and make a gating Result node immediately above whatever
       * plan node the pseudoconstant clause is assigned to.      It's usually best
       * to put a gating node as high in the plan tree as possible. If we are
       * not below an outer join, we can actually push the pseudoconstant qual
       * all the way to the top of the tree.    If we are below an outer join, we
       * leave the qual at its original syntactic level (we could push it up to
       * just below the outer join, but that seems more complex than it's
       * worth).
       */
      if (bms_is_empty(relids))
      {
            if (ojscope)
            {
                  /* clause is attached to outer join, eval it there */
                  relids = bms_copy(ojscope);
                  /* mustn't use as gating qual, so don't mark pseudoconstant */
            }
            else
            {
                  /* eval at original syntactic level */
                  relids = bms_copy(qualscope);
                  if (!contain_volatile_functions(clause))
                  {
                        /* mark as gating qual */
                        pseudoconstant = true;
                        /* tell createplan.c to check for gating quals */
                        root->hasPseudoConstantQuals = true;
                        /* if not below outer join, push it to top of tree */
                        if (!below_outer_join)
                              relids =
                                    get_relids_in_jointree((Node *) root->parse->jointree,
                                                                     false);
                  }
            }
      }

      /*----------
       * Check to see if clause application must be delayed by outer-join
       * considerations.
       *
       * A word about is_pushed_down: we mark the qual as "pushed down" if
       * it is (potentially) applicable at a level different from its original
       * syntactic level.  This flag is used to distinguish OUTER JOIN ON quals
       * from other quals pushed down to the same joinrel.  The rules are:
       *          WHERE quals and INNER JOIN quals: is_pushed_down = true.
       *          Non-degenerate OUTER JOIN quals: is_pushed_down = false.
       *          Degenerate OUTER JOIN quals: is_pushed_down = true.
       * A "degenerate" OUTER JOIN qual is one that doesn't mention the
       * non-nullable side, and hence can be pushed down into the nullable side
       * without changing the join result.  It is correct to treat it as a
       * regular filter condition at the level where it is evaluated.
       *
       * Note: it is not immediately obvious that a simple boolean is enough
       * for this: if for some reason we were to attach a degenerate qual to
       * its original join level, it would need to be treated as an outer join
       * qual there.    However, this cannot happen, because all the rels the
       * clause mentions must be in the outer join's min_righthand, therefore
       * the join it needs must be formed before the outer join; and we always
       * attach quals to the lowest level where they can be evaluated.  But
       * if we were ever to re-introduce a mechanism for delaying evaluation
       * of "expensive" quals, this area would need work.
       *----------
       */
      if (is_deduced)
      {
            /*
             * If the qual came from implied-equality deduction, it should not be
             * outerjoin-delayed, else deducer blew it.  But we can't check this
             * because the join_info_list may now contain OJs above where the qual
             * belongs.
             */
            Assert(!ojscope);
            is_pushed_down = true;
            outerjoin_delayed = false;
            /* Don't feed it back for more deductions */
            maybe_equivalence = false;
            maybe_outer_join = false;
      }
      else if (bms_overlap(relids, outerjoin_nonnullable))
      {
            /*
             * The qual is attached to an outer join and mentions (some of the)
             * rels on the nonnullable side, so it's not degenerate.
             *
             * We can't use such a clause to deduce equivalence (the left and
             * right sides might be unequal above the join because one of them has
             * gone to NULL) ... but we might be able to use it for more limited
             * deductions, if it is mergejoinable.  So consider adding it to the
             * lists of set-aside outer-join clauses.
             */
            is_pushed_down = false;
            maybe_equivalence = false;
            maybe_outer_join = true;

            /* Check to see if must be delayed by lower outer join */
            outerjoin_delayed = check_outerjoin_delay(root, &relids, false);

            /*
             * Now force the qual to be evaluated exactly at the level of joining
             * corresponding to the outer join.  We cannot let it get pushed down
             * into the nonnullable side, since then we'd produce no output rows,
             * rather than the intended single null-extended row, for any
             * nonnullable-side rows failing the qual.
             *
             * (Do this step after calling check_outerjoin_delay, because that
             * trashes relids.)
             */
            Assert(ojscope);
            relids = ojscope;
            Assert(!pseudoconstant);
      }
      else
      {
            /*
             * Normal qual clause or degenerate outer-join clause.      Either way, we
             * can mark it as pushed-down.
             */
            is_pushed_down = true;

            /* Check to see if must be delayed by lower outer join */
            outerjoin_delayed = check_outerjoin_delay(root, &relids, true);

            if (outerjoin_delayed)
            {
                  /* Should still be a subset of current scope ... */
                  Assert(bms_is_subset(relids, qualscope));

                  /*
                   * Because application of the qual will be delayed by outer join,
                   * we mustn't assume its vars are equal everywhere.
                   */
                  maybe_equivalence = false;

                  /*
                   * It's possible that this is an IS NULL clause that's redundant
                   * with a lower antijoin; if so we can just discard it.  We need
                   * not test in any of the other cases, because this will only
                   * be possible for pushed-down, delayed clauses.
                   */
                  if (check_redundant_nullability_qual(root, clause))
                        return;
            }
            else
            {
                  /*
                   * Qual is not delayed by any lower outer-join restriction, so we
                   * can consider feeding it to the equivalence machinery. However,
                   * if it's itself within an outer-join clause, treat it as though
                   * it appeared below that outer join (note that we can only get
                   * here when the clause references only nullable-side rels).
                   */
                  maybe_equivalence = true;
                  if (outerjoin_nonnullable != NULL)
                        below_outer_join = true;
            }

            /*
             * Since it doesn't mention the LHS, it's certainly not useful as a
             * set-aside OJ clause, even if it's in an OJ.
             */
            maybe_outer_join = false;
      }

      /*
       * Build the RestrictInfo node itself.
       */
      restrictinfo = make_restrictinfo((Expr *) clause,
                                                       is_pushed_down,
                                                       outerjoin_delayed,
                                                       pseudoconstant,
                                                       relids);

      /*
       * If it's a join clause (either naturally, or because delayed by
       * outer-join rules), add vars used in the clause to targetlists of their
       * relations, so that they will be emitted by the plan nodes that scan
       * those relations (else they won't be available at the join node!).
       *
       * Note: if the clause gets absorbed into an EquivalenceClass then this
       * may be unnecessary, but for now we have to do it to cover the case
       * where the EC becomes ec_broken and we end up reinserting the original
       * clauses into the plan.
       */
      if (bms_membership(relids) == BMS_MULTIPLE)
      {
            List     *vars = pull_var_clause(clause, true);

            add_vars_to_targetlist(root, vars, relids);
            list_free(vars);
      }

      /*
       * We check "mergejoinability" of every clause, not only join clauses,
       * because we want to know about equivalences between vars of the same
       * relation, or between vars and consts.
       */
      check_mergejoinable(restrictinfo);

      /*
       * If it is a true equivalence clause, send it to the EquivalenceClass
       * machinery.  We do *not* attach it directly to any restriction or join
       * lists.  The EC code will propagate it to the appropriate places later.
       *
       * If the clause has a mergejoinable operator and is not
       * outerjoin-delayed, yet isn't an equivalence because it is an outer-join
       * clause, the EC code may yet be able to do something with it.  We add it
       * to appropriate lists for further consideration later.  Specifically:
       *
       * If it is a left or right outer-join qualification that relates the two
       * sides of the outer join (no funny business like leftvar1 = leftvar2 +
       * rightvar), we add it to root->left_join_clauses or
       * root->right_join_clauses according to which side the nonnullable
       * variable appears on.
       *
       * If it is a full outer-join qualification, we add it to
       * root->full_join_clauses.  (Ideally we'd discard cases that aren't
       * leftvar = rightvar, as we do for left/right joins, but this routine
       * doesn't have the info needed to do that; and the current usage of the
       * full_join_clauses list doesn't require that, so it's not currently
       * worth complicating this routine's API to make it possible.)
       *
       * If none of the above hold, pass it off to
       * distribute_restrictinfo_to_rels().
       */
      if (restrictinfo->mergeopfamilies)
      {
            if (maybe_equivalence)
            {
                  if (process_equivalence(root, restrictinfo, below_outer_join))
                        return;
                  /* EC rejected it, so pass to distribute_restrictinfo_to_rels */
            }
            else if (maybe_outer_join && restrictinfo->can_join)
            {
                  if (bms_is_subset(restrictinfo->left_relids,
                                            outerjoin_nonnullable) &&
                        !bms_overlap(restrictinfo->right_relids,
                                           outerjoin_nonnullable))
                  {
                        /* we have outervar = innervar */
                        root->left_join_clauses = lappend(root->left_join_clauses,
                                                                          restrictinfo);
                        return;
                  }
                  if (bms_is_subset(restrictinfo->right_relids,
                                            outerjoin_nonnullable) &&
                        !bms_overlap(restrictinfo->left_relids,
                                           outerjoin_nonnullable))
                  {
                        /* we have innervar = outervar */
                        root->right_join_clauses = lappend(root->right_join_clauses,
                                                                           restrictinfo);
                        return;
                  }
                  if (jointype == JOIN_FULL)
                  {
                        /* FULL JOIN (above tests cannot match in this case) */
                        root->full_join_clauses = lappend(root->full_join_clauses,
                                                                          restrictinfo);
                        return;
                  }
            }
      }

      /* No EC special case applies, so push it into the clause lists */
      distribute_restrictinfo_to_rels(root, restrictinfo);
}

/*
 * check_outerjoin_delay
 *          Detect whether a qual referencing the given relids must be delayed
 *          in application due to the presence of a lower outer join, and/or
 *          may force extra delay of higher-level outer joins.
 *
 * If the qual must be delayed, add relids to *relids_p to reflect the lowest
 * safe level for evaluating the qual, and return TRUE.  Any extra delay for
 * higher-level joins is reflected by setting delay_upper_joins to TRUE in
 * SpecialJoinInfo structs.
 *
 * For an is_pushed_down qual, we can evaluate the qual as soon as (1) we have
 * all the rels it mentions, and (2) we are at or above any outer joins that
 * can null any of these rels and are below the syntactic location of the
 * given qual.    We must enforce (2) because pushing down such a clause below
 * the OJ might cause the OJ to emit null-extended rows that should not have
 * been formed, or that should have been rejected by the clause.  (This is
 * only an issue for non-strict quals, since if we can prove a qual mentioning
 * only nullable rels is strict, we'd have reduced the outer join to an inner
 * join in reduce_outer_joins().)
 *
 * To enforce (2), scan the join_info_list and merge the required-relid sets of
 * any such OJs into the clause's own reference list.  At the time we are
 * called, the join_info_list contains only outer joins below this qual.  We
 * have to repeat the scan until no new relids get added; this ensures that
 * the qual is suitably delayed regardless of the order in which OJs get
 * executed.  As an example, if we have one OJ with LHS=A, RHS=B, and one with
 * LHS=B, RHS=C, it is implied that these can be done in either order; if the
 * B/C join is done first then the join to A can null C, so a qual actually
 * mentioning only C cannot be applied below the join to A.
 *
 * For a non-pushed-down qual, this isn't going to determine where we place the
 * qual, but we need to determine outerjoin_delayed anyway for possible use
 * in reconsider_outer_join_clauses().
 *
 * Lastly, a pushed-down qual that references the nullable side of any current
 * join_info_list member and has to be evaluated above that OJ (because its
 * required relids overlap the LHS too) causes that OJ's delay_upper_joins
 * flag to be set TRUE.  This will prevent any higher-level OJs from
 * being interchanged with that OJ, which would result in not having any
 * correct place to evaluate the qual.    (The case we care about here is a
 * sub-select WHERE clause within the RHS of some outer join.  The WHERE
 * clause must effectively be treated as a degenerate clause of that outer
 * join's condition.  Rather than trying to match such clauses with joins
 * directly, we set delay_upper_joins here, and when the upper outer join
 * is processed by make_outerjoininfo, it will refrain from allowing the
 * two OJs to commute.)
 */
static bool
check_outerjoin_delay(PlannerInfo *root, Relids *relids_p,
                                bool is_pushed_down)
{
      Relids            relids = *relids_p;
      bool        outerjoin_delayed;
      bool        found_some;

      outerjoin_delayed = false;
      do
      {
            ListCell   *l;

            found_some = false;
            foreach(l, root->join_info_list)
            {
                  SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);

                  /* do we reference any nullable rels of this OJ? */
                  if (bms_overlap(relids, sjinfo->min_righthand) ||
                        (sjinfo->jointype == JOIN_FULL &&
                         bms_overlap(relids, sjinfo->min_lefthand)))
                  {
                        /* yes, so set the result flag */
                        outerjoin_delayed = true;
                        /* have we included all its rels in relids? */
                        if (!bms_is_subset(sjinfo->min_lefthand, relids) ||
                              !bms_is_subset(sjinfo->min_righthand, relids))
                        {
                              /* no, so add them in */
                              relids = bms_add_members(relids, sjinfo->min_lefthand);
                              relids = bms_add_members(relids, sjinfo->min_righthand);
                              /* we'll need another iteration */
                              found_some = true;
                        }
                        /* set delay_upper_joins if needed */
                        if (is_pushed_down && sjinfo->jointype != JOIN_FULL &&
                              bms_overlap(relids, sjinfo->min_lefthand))
                              sjinfo->delay_upper_joins = true;
                  }
            }
      } while (found_some);

      *relids_p = relids;
      return outerjoin_delayed;
}

/*
 * check_redundant_nullability_qual
 *      Check to see if the qual is an IS NULL qual that is redundant with
 *      a lower JOIN_ANTI join.
 *
 * We want to suppress redundant IS NULL quals, not so much to save cycles
 * as to avoid generating bogus selectivity estimates for them.  So if
 * redundancy is detected here, distribute_qual_to_rels() just throws away
 * the qual.
 */
static bool
check_redundant_nullability_qual(PlannerInfo *root, Node *clause)
{
      Var            *forced_null_var;
      Index       forced_null_rel;
      ListCell   *lc;

      /* Check for IS NULL, and identify the Var forced to NULL */
      forced_null_var = find_forced_null_var(clause);
      if (forced_null_var == NULL)
            return false;
      forced_null_rel = forced_null_var->varno;

      /*
       * If the Var comes from the nullable side of a lower antijoin, the
       * IS NULL condition is necessarily true.
       */
      foreach(lc, root->join_info_list)
      {
            SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);

            if (sjinfo->jointype == JOIN_ANTI &&
                  bms_is_member(forced_null_rel, sjinfo->syn_righthand))
                  return true;
      }

      return false;
}

/*
 * distribute_restrictinfo_to_rels
 *      Push a completed RestrictInfo into the proper restriction or join
 *      clause list(s).
 *
 * This is the last step of distribute_qual_to_rels() for ordinary qual
 * clauses.  Clauses that are interesting for equivalence-class processing
 * are diverted to the EC machinery, but may ultimately get fed back here.
 */
void
distribute_restrictinfo_to_rels(PlannerInfo *root,
                                                RestrictInfo *restrictinfo)
{
      Relids            relids = restrictinfo->required_relids;
      RelOptInfo *rel;

      switch (bms_membership(relids))
      {
            case BMS_SINGLETON:

                  /*
                   * There is only one relation participating in the clause, so it
                   * is a restriction clause for that relation.
                   */
                  rel = find_base_rel(root, bms_singleton_member(relids));

                  /* Add clause to rel's restriction list */
                  rel->baserestrictinfo = lappend(rel->baserestrictinfo,
                                                                  restrictinfo);
                  break;
            case BMS_MULTIPLE:

                  /*
                   * The clause is a join clause, since there is more than one rel
                   * in its relid set.
                   */

                  /*
                   * Check for hashjoinable operators.  (We don't bother setting the
                   * hashjoin info if we're not going to need it.)
                   */
                  if (enable_hashjoin)
                        check_hashjoinable(restrictinfo);

                  /*
                   * Add clause to the join lists of all the relevant relations.
                   */
                  add_join_clause_to_rels(root, restrictinfo, relids);
                  break;
            default:

                  /*
                   * clause references no rels, and therefore we have no place to
                   * attach it.  Shouldn't get here if callers are working properly.
                   */
                  elog(ERROR, "cannot cope with variable-free clause");
                  break;
      }
}

/*
 * process_implied_equality
 *      Create a restrictinfo item that says "item1 op item2", and push it
 *      into the appropriate lists.  (In practice opno is always a btree
 *      equality operator.)
 *
 * "qualscope" is the nominal syntactic level to impute to the restrictinfo.
 * This must contain at least all the rels used in the expressions, but it
 * is used only to set the qual application level when both exprs are
 * variable-free.  Otherwise the qual is applied at the lowest join level
 * that provides all its variables.
 *
 * "both_const" indicates whether both items are known pseudo-constant;
 * in this case it is worth applying eval_const_expressions() in case we
 * can produce constant TRUE or constant FALSE.  (Otherwise it's not,
 * because the expressions went through eval_const_expressions already.)
 *
 * This is currently used only when an EquivalenceClass is found to
 * contain pseudoconstants.  See path/pathkeys.c for more details.
 */
void
process_implied_equality(PlannerInfo *root,
                                     Oid opno,
                                     Expr *item1,
                                     Expr *item2,
                                     Relids qualscope,
                                     bool below_outer_join,
                                     bool both_const)
{
      Expr     *clause;

      /*
       * Build the new clause.  Copy to ensure it shares no substructure with
       * original (this is necessary in case there are subselects in there...)
       */
      clause = make_opclause(opno,
                                       BOOLOID,       /* opresulttype */
                                       false,         /* opretset */
                                       (Expr *) copyObject(item1),
                                       (Expr *) copyObject(item2));

      /* If both constant, try to reduce to a boolean constant. */
      if (both_const)
      {
            clause = (Expr *) eval_const_expressions(root, (Node *) clause);

            /* If we produced const TRUE, just drop the clause */
            if (clause && IsA(clause, Const))
            {
                  Const    *cclause = (Const *) clause;

                  Assert(cclause->consttype == BOOLOID);
                  if (!cclause->constisnull && DatumGetBool(cclause->constvalue))
                        return;
            }
      }

      /* Make a copy of qualscope to avoid problems if source EC changes */
      qualscope = bms_copy(qualscope);

      /*
       * Push the new clause into all the appropriate restrictinfo lists.
       */
      distribute_qual_to_rels(root, (Node *) clause,
                                          true, below_outer_join, JOIN_INNER,
                                          qualscope, NULL, NULL);
}

/*
 * build_implied_join_equality --- build a RestrictInfo for a derived equality
 *
 * This overlaps the functionality of process_implied_equality(), but we
 * must return the RestrictInfo, not push it into the joininfo tree.
 */
RestrictInfo *
build_implied_join_equality(Oid opno,
                                          Expr *item1,
                                          Expr *item2,
                                          Relids qualscope)
{
      RestrictInfo *restrictinfo;
      Expr     *clause;

      /*
       * Build the new clause.  Copy to ensure it shares no substructure with
       * original (this is necessary in case there are subselects in there...)
       */
      clause = make_opclause(opno,
                                       BOOLOID,       /* opresulttype */
                                       false,         /* opretset */
                                       (Expr *) copyObject(item1),
                                       (Expr *) copyObject(item2));

      /* Make a copy of qualscope to avoid problems if source EC changes */
      qualscope = bms_copy(qualscope);

      /*
       * Build the RestrictInfo node itself.
       */
      restrictinfo = make_restrictinfo(clause,
                                                       true,            /* is_pushed_down */
                                                       false,           /* outerjoin_delayed */
                                                       false,           /* pseudoconstant */
                                                       qualscope);

      /* Set mergejoinability info always, and hashjoinability if enabled */
      check_mergejoinable(restrictinfo);
      if (enable_hashjoin)
            check_hashjoinable(restrictinfo);

      return restrictinfo;
}


/*****************************************************************************
 *
 *     CHECKS FOR MERGEJOINABLE AND HASHJOINABLE CLAUSES
 *
 *****************************************************************************/

/*
 * check_mergejoinable
 *      If the restrictinfo's clause is mergejoinable, set the mergejoin
 *      info fields in the restrictinfo.
 *
 *      Currently, we support mergejoin for binary opclauses where
 *      the operator is a mergejoinable operator.  The arguments can be
 *      anything --- as long as there are no volatile functions in them.
 */
static void
check_mergejoinable(RestrictInfo *restrictinfo)
{
      Expr     *clause = restrictinfo->clause;
      Oid               opno;

      if (restrictinfo->pseudoconstant)
            return;
      if (!is_opclause(clause))
            return;
      if (list_length(((OpExpr *) clause)->args) != 2)
            return;

      opno = ((OpExpr *) clause)->opno;

      if (op_mergejoinable(opno) &&
            !contain_volatile_functions((Node *) clause))
            restrictinfo->mergeopfamilies = get_mergejoin_opfamilies(opno);

      /*
       * Note: op_mergejoinable is just a hint; if we fail to find the operator
       * in any btree opfamilies, mergeopfamilies remains NIL and so the clause
       * is not treated as mergejoinable.
       */
}

/*
 * check_hashjoinable
 *      If the restrictinfo's clause is hashjoinable, set the hashjoin
 *      info fields in the restrictinfo.
 *
 *      Currently, we support hashjoin for binary opclauses where
 *      the operator is a hashjoinable operator.      The arguments can be
 *      anything --- as long as there are no volatile functions in them.
 */
static void
check_hashjoinable(RestrictInfo *restrictinfo)
{
      Expr     *clause = restrictinfo->clause;
      Oid               opno;

      if (restrictinfo->pseudoconstant)
            return;
      if (!is_opclause(clause))
            return;
      if (list_length(((OpExpr *) clause)->args) != 2)
            return;

      opno = ((OpExpr *) clause)->opno;

      if (op_hashjoinable(opno) &&
            !contain_volatile_functions((Node *) clause))
            restrictinfo->hashjoinoperator = opno;
}

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