Store information about elided nodes in the final plan.

An extension (or core code) might want to reconstruct the planner's
choice of join order from the final plan. To do so, it must be possible
to find all of the RTIs that were part of the join problem in that plan.
The previous commit, together with the earlier work in
8c49a484e8ebb0199fba4bd68eaaedaf49b48ed0, is enough to let us match up
RTIs we see in the final plan with RTIs that we see during the planning
cycle, but we still have a problem if the planner decides to drop some
RTIs out of the final plan altogether.

To fix that, when setrefs.c removes a SubqueryScan, single-child Append,
or single-child MergeAppend from the final Plan tree, record the type of
the removed node and the RTIs that the removed node would have scanned
in the final plan tree. It would be natural to record this information
on the child of the removed plan node, but that would require adding
an additional pointer field to type Plan, which seems undesirable.
So, instead, store the information in a separate list that the
executor need never consult, and use the plan_node_id to identify
the plan node with which the removed node is logically associated.

Also, update pg_overexplain to display these details.

diff --git a/contrib/pg_overexplain/expected/pg_overexplain.out b/contrib/pg_overexplain/expected/pg_overexplain.out
index 55d34666d87f84e76ffa8bb417ef82a45cfd82f2..ca9a23ea61f6b17d1b285f9e6e41b7b3079d7a21 100644 (file)
--- a/contrib/pg_overexplain/expected/pg_overexplain.out
+++ b/contrib/pg_overexplain/expected/pg_overexplain.out
@@ -452,6 +452,8 @@ SELECT * FROM vegetables WHERE genus = 'daucus';
  Seq Scan on daucus vegetables
    Filter: (genus = 'daucus'::text)
    Scan RTI: 2
+   Elided Node Type: Append
+   Elided Node RTIs: 1
  RTI 1 (relation, inherited, in-from-clause):
    Eref: vegetables (id, name, genus)
    Relation: vegetables
@@ -465,7 +467,7 @@ SELECT * FROM vegetables WHERE genus = 'daucus';
    Relation Kind: relation
    Relation Lock Mode: AccessShareLock
  Unprunable RTIs: 1 2
-(16 rows)
+(18 rows)
 
 -- Also test a case that involves a write.
 EXPLAIN (RANGE_TABLE, COSTS OFF)

diff --git a/contrib/pg_overexplain/pg_overexplain.c b/contrib/pg_overexplain/pg_overexplain.c
index 1c4c796adb2317dd46c8c09b94f1e1372cc57f69..e54f8cfc332cbe1c0b8d4f76e7a4cf6238274148 100644 (file)
--- a/contrib/pg_overexplain/pg_overexplain.c
+++ b/contrib/pg_overexplain/pg_overexplain.c
@@ -191,6 +191,8 @@ overexplain_per_node_hook(PlanState *planstate, List *ancestors,
         */
        if (options->range_table)
        {
+               bool            opened_elided_nodes = false;
+
                switch (nodeTag(plan))
                {
                        case T_SeqScan:
@@ -251,6 +253,43 @@ overexplain_per_node_hook(PlanState *planstate, List *ancestors,
                        default:
                                break;
                }
+
+               foreach_node(ElidedNode, n, es->pstmt->elidedNodes)
+               {
+                       char       *elidednodetag;
+
+                       if (n->plan_node_id != plan->plan_node_id)
+                               continue;
+
+                       if (!opened_elided_nodes)
+                       {
+                               ExplainOpenGroup("Elided Nodes", "Elided Nodes", false, es);
+                               opened_elided_nodes = true;
+                       }
+
+                       switch (n->elided_type)
+                       {
+                               case T_Append:
+                                       elidednodetag = "Append";
+                                       break;
+                               case T_MergeAppend:
+                                       elidednodetag = "MergeAppend";
+                                       break;
+                               case T_SubqueryScan:
+                                       elidednodetag = "SubqueryScan";
+                                       break;
+                               default:
+                                       elidednodetag = psprintf("%d", n->elided_type);
+                                       break;
+                       }
+
+                       ExplainOpenGroup("Elided Node", NULL, true, es);
+                       ExplainPropertyText("Elided Node Type", elidednodetag, es);
+                       overexplain_bitmapset("Elided Node RTIs", n->relids, es);
+                       ExplainCloseGroup("Elided Node", NULL, true, es);
+               }
+               if (opened_elided_nodes)
+                       ExplainCloseGroup("Elided Nodes", "Elided Nodes", false, es);
        }
 }
 

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 31dcbdf3422c7b2f360ebf5c0cfded1d1aabf687..df9d03d549298aba946dae9a1daeb3a93efd5026 100644 (file)
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -618,6 +618,7 @@ standard_planner(Query *parse, const char *query_string, int cursorOptions,
        result->paramExecTypes = glob->paramExecTypes;
        /* utilityStmt should be null, but we might as well copy it */
        result->utilityStmt = parse->utilityStmt;
+       result->elidedNodes = glob->elidedNodes;
        result->stmt_location = parse->stmt_location;
        result->stmt_len = parse->stmt_len;
 

diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index edcd4aaa53e3575d2d9420a93ac75d23d8a39d8f..407ec39b63b15e606f94607494cf1253c10f7c23 100644 (file)
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -211,6 +211,9 @@ static List *set_windowagg_runcondition_references(PlannerInfo *root,
                                                                                                   List *runcondition,
                                                                                                   Plan *plan);
 
+static void record_elided_node(PlannerGlobal *glob, int plan_node_id,
+                                                          NodeTag elided_type, Bitmapset *relids);
+
 
 /*****************************************************************************
  *
@@ -1460,10 +1463,17 @@ set_subqueryscan_references(PlannerInfo *root,
 
        if (trivial_subqueryscan(plan))
        {
+               Index           scanrelid;
+
                /*
                 * We can omit the SubqueryScan node and just pull up the subplan.
                 */
                result = clean_up_removed_plan_level((Plan *) plan, plan->subplan);
+
+               /* Remember that we removed a SubqueryScan */
+               scanrelid = plan->scan.scanrelid + rtoffset;
+               record_elided_node(root->glob, plan->subplan->plan_node_id,
+                                                  T_SubqueryScan, bms_make_singleton(scanrelid));
        }
        else
        {
@@ -1891,7 +1901,17 @@ set_append_references(PlannerInfo *root,
                Plan       *p = (Plan *) linitial(aplan->appendplans);
 
                if (p->parallel_aware == aplan->plan.parallel_aware)
-                       return clean_up_removed_plan_level((Plan *) aplan, p);
+               {
+                       Plan       *result;
+
+                       result = clean_up_removed_plan_level((Plan *) aplan, p);
+
+                       /* Remember that we removed an Append */
+                       record_elided_node(root->glob, p->plan_node_id, T_Append,
+                                                          offset_relid_set(aplan->apprelids, rtoffset));
+
+                       return result;
+               }
        }
 
        /*
@@ -1959,7 +1979,17 @@ set_mergeappend_references(PlannerInfo *root,
                Plan       *p = (Plan *) linitial(mplan->mergeplans);
 
                if (p->parallel_aware == mplan->plan.parallel_aware)
-                       return clean_up_removed_plan_level((Plan *) mplan, p);
+               {
+                       Plan       *result;
+
+                       result = clean_up_removed_plan_level((Plan *) mplan, p);
+
+                       /* Remember that we removed a MergeAppend */
+                       record_elided_node(root->glob, p->plan_node_id, T_MergeAppend,
+                                                          offset_relid_set(mplan->apprelids, rtoffset));
+
+                       return result;
+               }
        }
 
        /*
@@ -3774,3 +3804,21 @@ extract_query_dependencies_walker(Node *node, PlannerInfo *context)
        return expression_tree_walker(node, extract_query_dependencies_walker,
                                                                  context);
 }
+
+/*
+ * Record some details about a node removed from the plan during setrefs
+ * processing, for the benefit of code trying to reconstruct planner decisions
+ * from examination of the final plan tree.
+ */
+static void
+record_elided_node(PlannerGlobal *glob, int plan_node_id,
+                                  NodeTag elided_type, Bitmapset *relids)
+{
+       ElidedNode *n = makeNode(ElidedNode);
+
+       n->plan_node_id = plan_node_id;
+       n->elided_type = elided_type;
+       n->relids = relids;
+
+       glob->elidedNodes = lappend(glob->elidedNodes, n);
+}

diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index 3782bc640754aba227898cff21b7d8bb8301ac80..42c146d802a9c964bcbfddea67b153e048082456 100644 (file)
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -159,6 +159,9 @@ typedef struct PlannerGlobal
        /* type OIDs for PARAM_EXEC Params */
        List       *paramExecTypes;
 
+       /* info about nodes elided from the plan during setrefs processing */
+       List       *elidedNodes;
+
        /* highest PlaceHolderVar ID assigned */
        Index           lastPHId;
 

diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 1526dd2ec6bdb2c276d2a715c7c2abe13bf41130..5d0520d5e58f642d995504b29639f389c76e47f3 100644 (file)
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -152,6 +152,9 @@ typedef struct PlannedStmt
        /* non-null if this is utility stmt */
        Node       *utilityStmt;
 
+       /* info about nodes elided from the plan during setrefs processing */
+       List       *elidedNodes;
+
        /*
         * DefElem objects added by extensions, e.g. using planner_shutdown_hook
         *
@@ -1838,4 +1841,18 @@ typedef struct SubPlanRTInfo
        bool            dummy;
 } SubPlanRTInfo;
 
+/*
+ * ElidedNode
+ *
+ * Information about nodes elided from the final plan tree: trivial subquery
+ * scans, and single-child Append and MergeAppend nodes.
+ */
+typedef struct ElidedNode
+{
+       NodeTag         type;
+       int                     plan_node_id;
+       NodeTag         elided_type;
+       Bitmapset  *relids;
+} ElidedNode;
+
 #endif                                                 /* PLANNODES_H */

diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 025bba87834508a0f8dcba7f0cee11d59545d4ad..8b300ae8233321fd7981bbefe088498ceb584c51 100644 (file)
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -701,6 +701,7 @@ EachState
 Edge
 EditableObjectType
 ElementsState
+ElidedNode
 EnableTimeoutParams
 EndDataPtrType
 EndDirectModify_function