mirror of https://github.com/postgres/postgres
Avoid O(N^2) cost when pulling up lots of UNION ALL subqueries.
perform_pullup_replace_vars() knows how to scan the whole parent query tree when we are replacing Vars during a subquery flattening operation. However, for the specific case of flattening a UNION ALL leaf query, that's mostly wasted work: the only place where relevant Vars could exist is in the AppendRelInfo that we just made for this leaf. Teaching perform_pullup_replace_vars() to just deal with that and exit is worthwhile because, if we have N such subqueries to pull up, we were spending O(N^2) work uselessly mutating the AppendRelInfos for all the other subqueries. While we're at it, avoid calling substitute_phv_relids if there are no PlaceHolderVars, and remove an obsolete check of parse->hasSubLinks. Andrey Lepikhov and Tom Lane Discussion: https://postgr.es/m/703c09a2-08f3-d2ec-b33d-dbecd62428b8@postgrespro.ru
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@ -128,7 +128,7 @@ static bool find_dependent_phvs_in_jointree(PlannerInfo *root,
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Node *node, int varno);
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static void substitute_phv_relids(Node *node,
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int varno, Relids subrelids);
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static void fix_append_rel_relids(List *append_rel_list, int varno,
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static void fix_append_rel_relids(PlannerInfo *root, int varno,
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Relids subrelids);
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static Node *find_jointree_node_for_rel(Node *jtnode, int relid);
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@ -1232,14 +1232,14 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
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* already checked that this won't require introducing multiple subrelids
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* into the single-slot AppendRelInfo structs.
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*/
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if (parse->hasSubLinks || root->glob->lastPHId != 0 ||
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root->append_rel_list)
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if (root->glob->lastPHId != 0 || root->append_rel_list)
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{
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Relids subrelids;
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subrelids = get_relids_in_jointree((Node *) subquery->jointree, false);
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substitute_phv_relids((Node *) parse, varno, subrelids);
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fix_append_rel_relids(root->append_rel_list, varno, subrelids);
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if (root->glob->lastPHId != 0)
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substitute_phv_relids((Node *) parse, varno, subrelids);
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fix_append_rel_relids(root, varno, subrelids);
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}
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/*
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@ -1418,7 +1418,10 @@ pull_up_union_leaf_queries(Node *setOp, PlannerInfo *root, int parentRTindex,
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/*
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* Recursively apply pull_up_subqueries to the new child RTE. (We
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* must build the AppendRelInfo first, because this will modify it.)
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* must build the AppendRelInfo first, because this will modify it;
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* indeed, that's the only part of the upper query where Vars
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* referencing childRTindex can exist at this point.)
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*
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* Note that we can pass NULL for containing-join info even if we're
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* actually under an outer join, because the child's expressions
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* aren't going to propagate up to the join. Also, we ignore the
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@ -2119,6 +2122,25 @@ perform_pullup_replace_vars(PlannerInfo *root,
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Query *parse = root->parse;
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ListCell *lc;
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/*
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* If we are considering an appendrel child subquery (that is, a UNION ALL
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* member query that we're pulling up), then the only part of the upper
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* query that could reference the child yet is the translated_vars list of
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* the associated AppendRelInfo. Furthermore, we do not need to insert
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* PHVs in the AppendRelInfo --- there isn't any outer join between.
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*/
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if (containing_appendrel)
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{
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bool save_need_phvs = rvcontext->need_phvs;
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rvcontext->need_phvs = false;
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containing_appendrel->translated_vars = (List *)
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pullup_replace_vars((Node *) containing_appendrel->translated_vars,
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rvcontext);
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rvcontext->need_phvs = save_need_phvs;
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return;
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}
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/*
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* Replace all of the top query's references to the subquery's outputs
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* with copies of the adjusted subtlist items, being careful not to
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@ -2172,22 +2194,14 @@ perform_pullup_replace_vars(PlannerInfo *root,
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parse->havingQual = pullup_replace_vars(parse->havingQual, rvcontext);
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/*
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* Replace references in the translated_vars lists of appendrels. When
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* pulling up an appendrel member, we do not need PHVs in the list of the
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* parent appendrel --- there isn't any outer join between. Elsewhere,
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* use PHVs for safety. (This analysis could be made tighter but it seems
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* unlikely to be worth much trouble.)
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* Replace references in the translated_vars lists of appendrels.
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*/
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foreach(lc, root->append_rel_list)
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{
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AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(lc);
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bool save_need_phvs = rvcontext->need_phvs;
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if (appinfo == containing_appendrel)
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rvcontext->need_phvs = false;
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appinfo->translated_vars = (List *)
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pullup_replace_vars((Node *) appinfo->translated_vars, rvcontext);
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rvcontext->need_phvs = save_need_phvs;
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}
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/*
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@ -3358,7 +3372,7 @@ remove_result_refs(PlannerInfo *root, int varno, Node *newjtloc)
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subrelids = get_relids_in_jointree(newjtloc, false);
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Assert(!bms_is_empty(subrelids));
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substitute_phv_relids((Node *) root->parse, varno, subrelids);
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fix_append_rel_relids(root->append_rel_list, varno, subrelids);
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fix_append_rel_relids(root, varno, subrelids);
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}
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/*
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@ -3577,7 +3591,7 @@ substitute_phv_relids(Node *node, int varno, Relids subrelids)
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* We assume we may modify the AppendRelInfo nodes in-place.
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*/
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static void
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fix_append_rel_relids(List *append_rel_list, int varno, Relids subrelids)
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fix_append_rel_relids(PlannerInfo *root, int varno, Relids subrelids)
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{
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ListCell *l;
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int subvarno = -1;
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@ -3588,7 +3602,7 @@ fix_append_rel_relids(List *append_rel_list, int varno, Relids subrelids)
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* AppendRelInfo nodes refer to it. So compute it on first use. Note that
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* bms_singleton_member will complain if set is not singleton.
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*/
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foreach(l, append_rel_list)
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foreach(l, root->append_rel_list)
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{
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AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
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@ -3603,8 +3617,9 @@ fix_append_rel_relids(List *append_rel_list, int varno, Relids subrelids)
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}
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/* Also fix up any PHVs in its translated vars */
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substitute_phv_relids((Node *) appinfo->translated_vars,
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varno, subrelids);
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if (root->glob->lastPHId != 0)
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substitute_phv_relids((Node *) appinfo->translated_vars,
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varno, subrelids);
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}
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}
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