planmain.c

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/*-------------------------------------------------------------------------
 *
 * planmain.c
 *    Routines to plan a single query
 *
 * What's in a name, anyway?  The top-level entry point of the planner/
 * optimizer is over in planner.c, not here as you might think from the
 * file name.  But this is the main code for planning a basic join operation,
 * shorn of features like subselects, inheritance, aggregates, grouping,
 * and so on.  (Those are the things planner.c deals with.)
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/optimizer/plan/planmain.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "optimizer/appendinfo.h"
#include "optimizer/clauses.h"
#include "optimizer/optimizer.h"
#include "optimizer/orclauses.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/placeholder.h"
#include "optimizer/planmain.h"
 
 
/*
 * query_planner
 *    Generate a path (that is, a simplified plan) for a basic query,
 *    which may involve joins but not any fancier features.
 *
 * Since query_planner does not handle the toplevel processing (grouping,
 * sorting, etc) it cannot select the best path by itself.  Instead, it
 * returns the RelOptInfo for the top level of joining, and the caller
 * (grouping_planner) can choose among the surviving paths for the rel.
 *
 * root describes the query to plan
 * qp_callback is a function to compute query_pathkeys once it's safe to do so
 * qp_extra is optional extra data to pass to qp_callback
 *
 * Note: the PlannerInfo node also includes a query_pathkeys field, which
 * tells query_planner the sort order that is desired in the final output
 * plan.  This value is *not* available at call time, but is computed by
 * qp_callback once we have completed merging the query's equivalence classes.
 * (We cannot construct canonical pathkeys until that's done.)
 */
RelOptInfo *
query_planner(PlannerInfo *root,
              query_pathkeys_callback qp_callback, void *qp_extra)
{
    Query      *parse = root->parse;
    List       *joinlist;
    RelOptInfo *final_rel;
 
    /*
     * Init planner lists to empty.
     *
     * NOTE: append_rel_list was set up by subquery_planner, so do not touch
     * here.
     */
    root->join_rel_list = NIL;
    root->join_rel_hash = NULL;
    root->join_rel_level = NULL;
    root->join_cur_level = 0;
    root->canon_pathkeys = NIL;
    root->left_join_clauses = NIL;
    root->right_join_clauses = NIL;
    root->full_join_clauses = NIL;
    root->join_info_list = NIL;
    root->placeholder_list = NIL;
    root->placeholder_array = NULL;
    root->placeholder_array_size = 0;
    root->fkey_list = NIL;
    root->initial_rels = NIL;
 
    /*
     * Set up arrays for accessing base relations and AppendRelInfos.
     */
    setup_simple_rel_arrays(root);
 
    /*
     * In the trivial case where the jointree is a single RTE_RESULT relation,
     * bypass all the rest of this function and just make a RelOptInfo and its
     * one access path.  This is worth optimizing because it applies for
     * common cases like "SELECT expression" and "INSERT ... VALUES()".
     */
    Assert(parse->jointree->fromlist != NIL);
    if (list_length(parse->jointree->fromlist) == 1)
    {
        Node       *jtnode = (Node *) linitial(parse->jointree->fromlist);
 
        if (IsA(jtnode, RangeTblRef))
        {
            int         varno = ((RangeTblRef *) jtnode)->rtindex;
            RangeTblEntry *rte = root->simple_rte_array[varno];
 
            Assert(rte != NULL);
            if (rte->rtekind == RTE_RESULT)
            {
                /* Make the RelOptInfo for it directly */
                final_rel = build_simple_rel(root, varno, NULL);
 
                /*
                 * If query allows parallelism in general, check whether the
                 * quals are parallel-restricted.  (We need not check
                 * final_rel->reltarget because it's empty at this point.
                 * Anything parallel-restricted in the query tlist will be
                 * dealt with later.)  We should always do this in a subquery,
                 * since it might be useful to use the subquery in parallel
                 * paths in the parent level.  At top level this is normally
                 * not worth the cycles, because a Result-only plan would
                 * never be interesting to parallelize.  However, if
                 * debug_parallel_query is on, then we want to execute the
                 * Result in a parallel worker if possible, so we must check.
                 */
                if (root->glob->parallelModeOK &&
                    (root->query_level > 1 ||
                     debug_parallel_query != DEBUG_PARALLEL_OFF))
                    final_rel->consider_parallel =
                        is_parallel_safe(root, parse->jointree->quals);
 
                /*
                 * The only path for it is a trivial Result path.  We cheat a
                 * bit here by using a GroupResultPath, because that way we
                 * can just jam the quals into it without preprocessing them.
                 * (But, if you hold your head at the right angle, a FROM-less
                 * SELECT is a kind of degenerate-grouping case, so it's not
                 * that much of a cheat.)
                 */
                add_path(final_rel, (Path *)
                         create_group_result_path(root, final_rel,
                                                  final_rel->reltarget,
                                                  (List *) parse->jointree->quals));
 
                /* Select cheapest path (pretty easy in this case...) */
                set_cheapest(final_rel);
 
                /*
                 * We don't need to run generate_base_implied_equalities, but
                 * we do need to pretend that EC merging is complete.
                 */
                root->ec_merging_done = true;
 
                /*
                 * We still are required to call qp_callback, in case it's
                 * something like "SELECT 2+2 ORDER BY 1".
                 */
                (*qp_callback) (root, qp_extra);
 
                return final_rel;
            }
        }
    }
 
    /*
     * Construct RelOptInfo nodes for all base relations used in the query.
     * Appendrel member relations ("other rels") will be added later.
     *
     * Note: the reason we find the baserels by searching the jointree, rather
     * than scanning the rangetable, is that the rangetable may contain RTEs
     * for rels not actively part of the query, for example views.  We don't
     * want to make RelOptInfos for them.
     */
    add_base_rels_to_query(root, (Node *) parse->jointree);
 
    /* Remove any redundant GROUP BY columns */
    remove_useless_groupby_columns(root);
 
    /*
     * Examine the targetlist and join tree, adding entries to baserel
     * targetlists for all referenced Vars, and generating PlaceHolderInfo
     * entries for all referenced PlaceHolderVars.  Restrict and join clauses
     * are added to appropriate lists belonging to the mentioned relations. We
     * also build EquivalenceClasses for provably equivalent expressions. The
     * SpecialJoinInfo list is also built to hold information about join order
     * restrictions.  Finally, we form a target joinlist for make_one_rel() to
     * work from.
     */
    build_base_rel_tlists(root, root->processed_tlist);
 
    find_placeholders_in_jointree(root);
 
    find_lateral_references(root);
 
    joinlist = deconstruct_jointree(root);
 
    /*
     * Reconsider any postponed outer-join quals now that we have built up
     * equivalence classes.  (This could result in further additions or
     * mergings of classes.)
     */
    reconsider_outer_join_clauses(root);
 
    /*
     * If we formed any equivalence classes, generate additional restriction
     * clauses as appropriate.  (Implied join clauses are formed on-the-fly
     * later.)
     */
    generate_base_implied_equalities(root);
 
    /*
     * We have completed merging equivalence sets, so it's now possible to
     * generate pathkeys in canonical form; so compute query_pathkeys and
     * other pathkeys fields in PlannerInfo.
     */
    (*qp_callback) (root, qp_extra);
 
    /*
     * Examine any "placeholder" expressions generated during subquery pullup.
     * Make sure that the Vars they need are marked as needed at the relevant
     * join level.  This must be done before join removal because it might
     * cause Vars or placeholders to be needed above a join when they weren't
     * so marked before.
     */
    fix_placeholder_input_needed_levels(root);
 
    /*
     * Remove any useless outer joins.  Ideally this would be done during
     * jointree preprocessing, but the necessary information isn't available
     * until we've built baserel data structures and classified qual clauses.
     */
    joinlist = remove_useless_joins(root, joinlist);
 
    /*
     * Also, reduce any semijoins with unique inner rels to plain inner joins.
     * Likewise, this can't be done until now for lack of needed info.
     */
    reduce_unique_semijoins(root);
 
    /*
     * Remove self joins on a unique column.
     */
    joinlist = remove_useless_self_joins(root, joinlist);
 
    /*
     * Now distribute "placeholders" to base rels as needed.  This has to be
     * done after join removal because removal could change whether a
     * placeholder is evaluable at a base rel.
     */
    add_placeholders_to_base_rels(root);
 
    /*
     * Construct the lateral reference sets now that we have finalized
     * PlaceHolderVar eval levels.
     */
    create_lateral_join_info(root);
 
    /*
     * Match foreign keys to equivalence classes and join quals.  This must be
     * done after finalizing equivalence classes, and it's useful to wait till
     * after join removal so that we can skip processing foreign keys
     * involving removed relations.
     */
    match_foreign_keys_to_quals(root);
 
    /*
     * Look for join OR clauses that we can extract single-relation
     * restriction OR clauses from.
     */
    extract_restriction_or_clauses(root);
 
    /*
     * Now expand appendrels by adding "otherrels" for their children.  We
     * delay this to the end so that we have as much information as possible
     * available for each baserel, including all restriction clauses.  That
     * let us prune away partitions that don't satisfy a restriction clause.
     * Also note that some information such as lateral_relids is propagated
     * from baserels to otherrels here, so we must have computed it already.
     */
    add_other_rels_to_query(root);
 
    /*
     * Distribute any UPDATE/DELETE/MERGE row identity variables to the target
     * relations.  This can't be done till we've finished expansion of
     * appendrels.
     */
    distribute_row_identity_vars(root);
 
    /*
     * Ready to do the primary planning.
     */
    final_rel = make_one_rel(root, joinlist);
 
    /* Check that we got at least one usable path */
    if (!final_rel || !final_rel->cheapest_total_path ||
        final_rel->cheapest_total_path->param_info != NULL)
        elog(ERROR, "failed to construct the join relation");
 
    return final_rel;
}