Improve inheritance_planner()'s performance for large inheritance sets.

Commit c03ad5602f529787968fa3201b35c119bbc6d782 introduced a planner
performance regression for UPDATE/DELETE on large inheritance sets.
It required copying the append_rel_list (which is of size proportional to
the number of inherited tables) once for each inherited table, thus
resulting in O(N^2) time and memory consumption.  While it's difficult to
avoid that in general, the extra work only has to be done for
append_rel_list entries that actually reference subquery RTEs, which
inheritance-set entries will not.  So we can buy back essentially all of
the loss in cases without subqueries in FROM; and even for those, the added
work is mainly proportional to the number of UNION ALL subqueries.

Back-patch to 9.2, like the previous commit.

Tom Lane and Dean Rasheed, per a complaint from Thomas Munro.

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index c19364e0018b38d338cfd2e22f9ab20245960ff4..0bb8d20d8e6eea0a20ecc217946bd9bbed89c0c5 100644 (file)
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -765,6 +765,8 @@ inheritance_planner(PlannerInfo *root)
 {
    Query      *parse = root->parse;
    int         parentRTindex = parse->resultRelation;
+   Bitmapset  *subqueryRTindexes;
+   Bitmapset  *modifiableARIindexes;
    List       *final_rtable = NIL;
    int         save_rel_array_size = 0;
    RelOptInfo **save_rel_array = NULL;
@@ -773,6 +775,7 @@ inheritance_planner(PlannerInfo *root)
    List       *returningLists = NIL;
    List       *rowMarks;
    ListCell   *lc;
+   Index       rti;
 
    /*
     * We generate a modified instance of the original Query for each target
@@ -788,13 +791,54 @@ inheritance_planner(PlannerInfo *root)
     * (1) would result in a rangetable of length O(N^2) for N targets, with
     * at least O(N^3) work expended here; and (2) would greatly complicate
     * management of the rowMarks list.
+    *
+    * To begin with, generate a bitmapset of the relids of the subquery RTEs.
+    */
+   subqueryRTindexes = NULL;
+   rti = 1;
+   foreach(lc, parse->rtable)
+   {
+       RangeTblEntry *rte = (RangeTblEntry *) lfirst(lc);
+
+       if (rte->rtekind == RTE_SUBQUERY)
+           subqueryRTindexes = bms_add_member(subqueryRTindexes, rti);
+       rti++;
+   }
+
+   /*
+    * Next, we want to identify which AppendRelInfo items contain references
+    * to any of the aforesaid subquery RTEs.  These items will need to be
+    * copied and modified to adjust their subquery references; whereas the
+    * other ones need not be touched.  It's worth being tense over this
+    * because we can usually avoid processing most of the AppendRelInfo
+    * items, thereby saving O(N^2) space and time when the target is a large
+    * inheritance tree.  We can identify AppendRelInfo items by their
+    * child_relid, since that should be unique within the list.
+    */
+   modifiableARIindexes = NULL;
+   if (subqueryRTindexes != NULL)
+   {
+       foreach(lc, root->append_rel_list)
+       {
+           AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(lc);
+
+           if (bms_is_member(appinfo->parent_relid, subqueryRTindexes) ||
+               bms_is_member(appinfo->child_relid, subqueryRTindexes) ||
+               bms_overlap(pull_varnos((Node *) appinfo->translated_vars),
+                           subqueryRTindexes))
+               modifiableARIindexes = bms_add_member(modifiableARIindexes,
+                                                     appinfo->child_relid);
+       }
+   }
+
+   /*
+    * And now we can get on with generating a plan for each child table.
     */
    foreach(lc, root->append_rel_list)
    {
        AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(lc);
        PlannerInfo subroot;
        Plan       *subplan;
-       Index       rti;
 
        /* append_rel_list contains all append rels; ignore others */
        if (appinfo->parent_relid != parentRTindex)
@@ -828,9 +872,29 @@ inheritance_planner(PlannerInfo *root)
        /*
         * The append_rel_list likewise might contain references to subquery
         * RTEs (if any subqueries were flattenable UNION ALLs).  So prepare
-        * to apply ChangeVarNodes to that, too.
+        * to apply ChangeVarNodes to that, too.  As explained above, we only
+        * want to copy items that actually contain such references; the rest
+        * can just get linked into the subroot's append_rel_list.
+        *
+        * If we know there are no such references, we can just use the outer
+        * append_rel_list unmodified.
         */
-       subroot.append_rel_list = (List *) copyObject(root->append_rel_list);
+       if (modifiableARIindexes != NULL)
+       {
+           ListCell   *lc2;
+
+           subroot.append_rel_list = NIL;
+           foreach(lc2, root->append_rel_list)
+           {
+               AppendRelInfo *appinfo2 = (AppendRelInfo *) lfirst(lc2);
+
+               if (bms_is_member(appinfo2->child_relid, modifiableARIindexes))
+                   appinfo2 = (AppendRelInfo *) copyObject(appinfo2);
+
+               subroot.append_rel_list = lappend(subroot.append_rel_list,
+                                                 appinfo2);
+           }
+       }
 
        /*
         * Add placeholders to the child Query's rangetable list to fill the
@@ -850,7 +914,7 @@ inheritance_planner(PlannerInfo *root)
         * since subquery RTEs couldn't contain any references to the target
         * rel.
         */
-       if (final_rtable != NIL)
+       if (final_rtable != NIL && subqueryRTindexes != NULL)
        {
            ListCell   *lr;
 
@@ -859,7 +923,7 @@ inheritance_planner(PlannerInfo *root)
            {
                RangeTblEntry *rte = (RangeTblEntry *) lfirst(lr);
 
-               if (rte->rtekind == RTE_SUBQUERY)
+               if (bms_is_member(rti, subqueryRTindexes))
                {
                    Index       newrti;
 
@@ -872,7 +936,20 @@ inheritance_planner(PlannerInfo *root)
                    newrti = list_length(subroot.parse->rtable) + 1;
                    ChangeVarNodes((Node *) subroot.parse, rti, newrti, 0);
                    ChangeVarNodes((Node *) subroot.rowMarks, rti, newrti, 0);
-                   ChangeVarNodes((Node *) subroot.append_rel_list, rti, newrti, 0);
+                   /* Skip processing unchanging parts of append_rel_list */
+                   if (modifiableARIindexes != NULL)
+                   {
+                       ListCell   *lc2;
+
+                       foreach(lc2, subroot.append_rel_list)
+                       {
+                           AppendRelInfo *appinfo2 = (AppendRelInfo *) lfirst(lc2);
+
+                           if (bms_is_member(appinfo2->child_relid,
+                                             modifiableARIindexes))
+                               ChangeVarNodes((Node *) appinfo2, rti, newrti, 0);
+                       }
+                   }
                    rte = copyObject(rte);
                    subroot.parse->rtable = lappend(subroot.parse->rtable,
                                                    rte);