pgpa_scan.c

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/*-------------------------------------------------------------------------
 *
 * pgpa_scan.c
 *    analysis of scans in Plan trees
 *
 * Copyright (c) 2016-2026, PostgreSQL Global Development Group
 *
 *    contrib/pg_plan_advice/pgpa_scan.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "pgpa_scan.h"
#include "pgpa_walker.h"
 
#include "nodes/parsenodes.h"
#include "parser/parsetree.h"
 
static pgpa_scan *pgpa_make_scan(pgpa_plan_walker_context *walker, Plan *plan,
                                 pgpa_scan_strategy strategy,
                                 Bitmapset *relids);
 
 
static RTEKind unique_nonjoin_rtekind(Bitmapset *relids, List *rtable);
 
/*
 * Build a pgpa_scan object for a Plan node and update the plan walker
 * context as appropriate.  If this is an Append or MergeAppend scan, also
 * build pgpa_scan for any scans that were consolidated into this one by
 * Append/MergeAppend pull-up.
 *
 * If there is at least one ElidedNode for this plan node, pass the uppermost
 * one as elided_node, else pass NULL.
 *
 * Set the 'beneath_any_gather' node if we are underneath a Gather or
 * Gather Merge node (except for a single-copy Gather node, for which
 * GATHER or GATHER_MERGE advice should not be emitted).
 *
 * Set the 'within_join_problem' flag if we're inside of a join problem and
 * not otherwise.
 */
pgpa_scan *
pgpa_build_scan(pgpa_plan_walker_context *walker, Plan *plan,
                ElidedNode *elided_node,
                bool beneath_any_gather, bool within_join_problem)
{
    pgpa_scan_strategy strategy = PGPA_SCAN_ORDINARY;
    Bitmapset  *relids = NULL;
    int         rti = -1;
    List       *child_append_relid_sets = NIL;
    NodeTag     nodetype = nodeTag(plan);
 
    if (elided_node != NULL)
    {
        nodetype = elided_node->elided_type;
        relids = elided_node->relids;
 
        /*
         * If setrefs processing elided an Append or MergeAppend node that had
         * only one surviving child, it could be either a partitionwise
         * operation or a setop over subqueries, depending on the rtekind.
         *
         * A setop over subqueries, or a trivial SubqueryScan that was elided,
         * is an "ordinary" scan i.e. one for which we do not need to generate
         * advice because the planner has not made any meaningful choice.
         *
         * Note that the PGPA_SCAN_PARTITIONWISE case also includes
         * partitionwise joins; this module considers those to be a form of
         * scan, since they lack internal structure that we can decompose.
         */
        if ((nodetype == T_Append || nodetype == T_MergeAppend) &&
            unique_nonjoin_rtekind(relids,
                                   walker->pstmt->rtable) == RTE_RELATION)
            strategy = PGPA_SCAN_PARTITIONWISE;
        else
            strategy = PGPA_SCAN_ORDINARY;
 
        /* Join RTIs can be present, but advice never refers to them. */
        relids = pgpa_filter_out_join_relids(relids, walker->pstmt->rtable);
    }
    else if ((rti = pgpa_scanrelid(plan)) != 0)
    {
        relids = bms_make_singleton(rti);
 
        switch (nodeTag(plan))
        {
            case T_SeqScan:
                strategy = PGPA_SCAN_SEQ;
                break;
            case T_BitmapHeapScan:
                strategy = PGPA_SCAN_BITMAP_HEAP;
                break;
            case T_IndexScan:
                strategy = PGPA_SCAN_INDEX;
                break;
            case T_IndexOnlyScan:
                strategy = PGPA_SCAN_INDEX_ONLY;
                break;
            case T_TidScan:
            case T_TidRangeScan:
                strategy = PGPA_SCAN_TID;
                break;
            default:
 
                /*
                 * This case includes a ForeignScan targeting a single
                 * relation; no other strategy is possible in that case, but
                 * see below, where things are different in multi-relation
                 * cases.
                 */
                strategy = PGPA_SCAN_ORDINARY;
                break;
        }
    }
    else if ((relids = pgpa_relids(plan)) != NULL)
    {
        switch (nodeTag(plan))
        {
            case T_ForeignScan:
 
                /*
                 * If multiple relations are being targeted by a single
                 * foreign scan, then the foreign join has been pushed to the
                 * remote side, and we want that to be reflected in the
                 * generated advice.
                 */
                strategy = PGPA_SCAN_FOREIGN;
                break;
            case T_Append:
 
                /*
                 * Append nodes can represent partitionwise scans of a
                 * relation, but when they implement a set operation, they are
                 * just ordinary scans.
                 */
                if (unique_nonjoin_rtekind(relids, walker->pstmt->rtable)
                    == RTE_RELATION)
                    strategy = PGPA_SCAN_PARTITIONWISE;
                else
                    strategy = PGPA_SCAN_ORDINARY;
 
                /* Be sure to account for pulled-up scans. */
                child_append_relid_sets =
                    ((Append *) plan)->child_append_relid_sets;
                break;
            case T_MergeAppend:
                /* Same logic here as for Append, above. */
                if (unique_nonjoin_rtekind(relids, walker->pstmt->rtable)
                    == RTE_RELATION)
                    strategy = PGPA_SCAN_PARTITIONWISE;
                else
                    strategy = PGPA_SCAN_ORDINARY;
 
                /* Be sure to account for pulled-up scans. */
                child_append_relid_sets =
                    ((MergeAppend *) plan)->child_append_relid_sets;
                break;
            default:
                strategy = PGPA_SCAN_ORDINARY;
                break;
        }
 
 
        /* Join RTIs can be present, but advice never refers to them. */
        relids = pgpa_filter_out_join_relids(relids, walker->pstmt->rtable);
    }
 
    /*
     * If this is an Append or MergeAppend node into which subordinate Append
     * or MergeAppend paths were merged, each of those merged paths is
     * effectively another scan for which we need to account.
     */
    foreach_node(Bitmapset, child_relids, child_append_relid_sets)
    {
        Bitmapset  *child_nonjoin_relids;
 
        child_nonjoin_relids =
            pgpa_filter_out_join_relids(child_relids,
                                        walker->pstmt->rtable);
        (void) pgpa_make_scan(walker, plan, strategy,
                              child_nonjoin_relids);
    }
 
    /*
     * If this plan node has no associated RTIs, it's not a scan. When the
     * 'within_join_problem' flag is set, that's unexpected, so throw an
     * error, else return quietly.
     */
    if (relids == NULL)
    {
        if (within_join_problem)
            elog(ERROR, "plan node has no RTIs: %d", (int) nodeTag(plan));
        return NULL;
    }
 
    /*
     * Add the appropriate set of RTIs to walker->no_gather_scans.
     *
     * Add nothing if we're beneath a Gather or Gather Merge node, since
     * NO_GATHER advice is clearly inappropriate in that situation.
     *
     * Add nothing if this is an Append or MergeAppend node, whether or not
     * elided. We'll emit NO_GATHER() for the underlying scan, which is good
     * enough.
     */
    if (!beneath_any_gather && nodetype != T_Append &&
        nodetype != T_MergeAppend)
        walker->no_gather_scans =
            bms_add_members(walker->no_gather_scans, relids);
 
    /* Caller tells us whether NO_GATHER() advice for this scan is needed. */
    return pgpa_make_scan(walker, plan, strategy, relids);
}
 
/*
 * Create a single pgpa_scan object and update the pgpa_plan_walker_context.
 */
static pgpa_scan *
pgpa_make_scan(pgpa_plan_walker_context *walker, Plan *plan,
               pgpa_scan_strategy strategy, Bitmapset *relids)
{
    pgpa_scan  *scan;
 
    /* Create the scan object. */
    scan = palloc(sizeof(pgpa_scan));
    scan->plan = plan;
    scan->strategy = strategy;
    scan->relids = relids;
 
    /* Add it to the appropriate list. */
    walker->scans[scan->strategy] = lappend(walker->scans[scan->strategy],
                                            scan);
 
    return scan;
}
 
/*
 * Determine the unique rtekind of a set of relids.
 */
static RTEKind
unique_nonjoin_rtekind(Bitmapset *relids, List *rtable)
{
    int         rti = -1;
    bool        first = true;
    RTEKind     rtekind;
 
    Assert(relids != NULL);
 
    while ((rti = bms_next_member(relids, rti)) >= 0)
    {
        RangeTblEntry *rte = rt_fetch(rti, rtable);
 
        if (rte->rtekind == RTE_JOIN)
            continue;
 
        if (first)
        {
            rtekind = rte->rtekind;
            first = false;
        }
        else if (rtekind != rte->rtekind)
            elog(ERROR, "rtekind mismatch: %d vs. %d",
                 rtekind, rte->rtekind);
    }
 
    if (first)
        elog(ERROR, "no non-RTE_JOIN RTEs found");
 
    return rtekind;
}