Fix improper repetition of previous results from a hashed aggregate.

ExecReScanAgg's check for whether it could re-use a previously calculated
hashtable neglected the possibility that the Agg node might reference
PARAM_EXEC Params that are not referenced by its input plan node.  That's
okay if the Params are in upper tlist or qual expressions; but if one
appears in aggregate input expressions, then the hashtable contents need
to be recomputed when the Param's value changes.

To avoid unnecessary performance degradation in the case of a Param that
isn't within an aggregate input, add logic to the planner to determine
which Params are within aggregate inputs.  This requires a new field in
struct Agg, but fortunately we never write plans to disk, so this isn't
an initdb-forcing change.

Per report from Jeevan Chalke.  This has been broken since forever,
so back-patch to all supported branches.

Andrew Gierth, with minor adjustments by me

Report: <CAM2+6=VY8ykfLT5Q8vb9B6EbeBk-NGuLbT6seaQ+Fq4zXvrDcA@mail.gmail.com>

diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index 2cc67ab6304622448d53f552d956f3d102cf4daa..842fd8574f38d6be76ff42ba04dedf0b6bc94db7 100644 (file)
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -1909,13 +1909,14 @@ void
 ExecReScanAgg(AggState *node)
 {
    ExprContext *econtext = node->ss.ps.ps_ExprContext;
+   Agg        *aggnode = (Agg *) node->ss.ps.plan;
    int         aggno;
 
    node->agg_done = false;
 
    node->ss.ps.ps_TupFromTlist = false;
 
-   if (((Agg *) node->ss.ps.plan)->aggstrategy == AGG_HASHED)
+   if (aggnode->aggstrategy == AGG_HASHED)
    {
        /*
         * In the hashed case, if we haven't yet built the hash table then we
@@ -1927,11 +1928,13 @@ ExecReScanAgg(AggState *node)
            return;
 
        /*
-        * If we do have the hash table and the subplan does not have any
-        * parameter changes, then we can just rescan the existing hash table;
-        * no need to build it again.
+        * If we do have the hash table, and the subplan does not have any
+        * parameter changes, and none of our own parameter changes affect
+        * input expressions of the aggregated functions, then we can just
+        * rescan the existing hash table; no need to build it again.
         */
-       if (node->ss.ps.lefttree->chgParam == NULL)
+       if (node->ss.ps.lefttree->chgParam == NULL &&
+           !bms_overlap(node->ss.ps.chgParam, aggnode->aggParams))
        {
            ResetTupleHashIterator(node->hashtable, &node->hashiter);
            return;
@@ -1968,7 +1971,7 @@ ExecReScanAgg(AggState *node)
     */
    MemoryContextResetAndDeleteChildren(node->aggcontext);
 
-   if (((Agg *) node->ss.ps.plan)->aggstrategy == AGG_HASHED)
+   if (aggnode->aggstrategy == AGG_HASHED)
    {
        /* Rebuild an empty hash table */
        build_hash_table(node);

diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index c9878e7bc5150e22978ad851fb6913e8c15ae252..62fd5bb2c55668c22124d4450d5171f029c213a6 100644 (file)
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -780,6 +780,7 @@ _copyAgg(const Agg *from)
        COPY_POINTER_FIELD(grpOperators, from->numCols * sizeof(Oid));
    }
    COPY_SCALAR_FIELD(numGroups);
+   COPY_BITMAPSET_FIELD(aggParams);
 
    return newnode;
 }

diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 12c8fed1ab9a8514a92dbe6bcea8e4014c92c6e2..1e26a0bb913fb060498af34723f5ef5c698497d7 100644 (file)
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -644,6 +644,7 @@ _outAgg(StringInfo str, const Agg *node)
        appendStringInfo(str, " %u", node->grpOperators[i]);
 
    WRITE_LONG_FIELD(numGroups);
+   WRITE_BITMAPSET_FIELD(aggParams);
 }
 
 static void

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 50c18508dc03218c8da3c3d17bcbbe0275fc6166..39a3259e5f103115862eea85f7508da39f607e9f 100644 (file)
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -4152,6 +4152,7 @@ make_agg(PlannerInfo *root, List *tlist, List *qual,
    node->grpColIdx = grpColIdx;
    node->grpOperators = grpOperators;
    node->numGroups = numGroups;
+   node->aggParams = NULL;     /* SS_finalize_plan() will fill this */
 
    copy_plan_costsize(plan, lefttree); /* only care about copying size */
    cost_agg(&agg_path, root,

diff --git a/src/backend/optimizer/plan/subselect.c b/src/backend/optimizer/plan/subselect.c
index 51704a1342ee0266fbda5a05dcaad33b2e4822fa..d7212f52d26ec6d95cf074ce8aba070a08e1c686 100644 (file)
--- a/src/backend/optimizer/plan/subselect.c
+++ b/src/backend/optimizer/plan/subselect.c
@@ -79,6 +79,7 @@ static Bitmapset *finalize_plan(PlannerInfo *root,
              Bitmapset *valid_params,
              Bitmapset *scan_params);
 static bool finalize_primnode(Node *node, finalize_primnode_context *context);
+static bool finalize_agg_primnode(Node *node, finalize_primnode_context *context);
 
 
 /*
@@ -2354,6 +2355,29 @@ finalize_plan(PlannerInfo *root, Plan *plan, Bitmapset *valid_params,
                                         locally_added_param);
            break;
 
+       case T_Agg:
+           {
+               Agg        *agg = (Agg *) plan;
+
+               /*
+                * AGG_HASHED plans need to know which Params are referenced
+                * in aggregate calls.  Do a separate scan to identify them.
+                */
+               if (agg->aggstrategy == AGG_HASHED)
+               {
+                   finalize_primnode_context aggcontext;
+
+                   aggcontext.root = root;
+                   aggcontext.paramids = NULL;
+                   finalize_agg_primnode((Node *) agg->plan.targetlist,
+                                         &aggcontext);
+                   finalize_agg_primnode((Node *) agg->plan.qual,
+                                         &aggcontext);
+                   agg->aggParams = aggcontext.paramids;
+               }
+           }
+           break;
+
        case T_WindowAgg:
            finalize_primnode(((WindowAgg *) plan)->startOffset,
                              &context);
@@ -2362,7 +2386,6 @@ finalize_plan(PlannerInfo *root, Plan *plan, Bitmapset *valid_params,
            break;
 
        case T_Hash:
-       case T_Agg:
        case T_Material:
        case T_Sort:
        case T_Unique:
@@ -2506,6 +2529,28 @@ finalize_primnode(Node *node, finalize_primnode_context *context)
                                  (void *) context);
 }
 
+/*
+ * finalize_agg_primnode: find all Aggref nodes in the given expression tree,
+ * and add IDs of all PARAM_EXEC params appearing within their aggregated
+ * arguments to the result set.
+ */
+static bool
+finalize_agg_primnode(Node *node, finalize_primnode_context *context)
+{
+   if (node == NULL)
+       return false;
+   if (IsA(node, Aggref))
+   {
+       Aggref     *agg = (Aggref *) node;
+
+       /* we should not consider the direct arguments, if any */
+       finalize_primnode((Node *) agg->args, context);
+       return false;           /* there can't be any Aggrefs below here */
+   }
+   return expression_tree_walker(node, finalize_agg_primnode,
+                                 (void *) context);
+}
+
 /*
  * SS_make_initplan_from_plan - given a plan tree, make it an InitPlan
  *

diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 827bfe4947c2e54d6e5fee1955e14193bb80eff7..bbf03e28f6c73783bc0291bae62d652b15c60de3 100644 (file)
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -632,6 +632,8 @@ typedef struct Agg
    AttrNumber *grpColIdx;      /* their indexes in the target list */
    Oid        *grpOperators;   /* equality operators to compare with */
    long        numGroups;      /* estimated number of groups in input */
+   Bitmapset  *aggParams;      /* IDs of Params used in Aggref inputs */
+   /* Note: planner provides numGroups & aggParams only in AGG_HASHED case */
 } Agg;
 
 /* ----------------

diff --git a/src/test/regress/expected/aggregates.out b/src/test/regress/expected/aggregates.out
index 6f0d20fbae73c855487d2167269c96894939cdb6..f571aea7e1daa592ebbac495342dbaa8572ad507 100644 (file)
--- a/src/test/regress/expected/aggregates.out
+++ b/src/test/regress/expected/aggregates.out
@@ -305,6 +305,38 @@ from tenk1 o;
  9999
 (1 row)
 
+-- Test handling of Params within aggregate arguments in hashed aggregation.
+-- Per bug report from Jeevan Chalke.
+explain (verbose, costs off)
+select array(select sum(x+y) s
+            from generate_series(1,3) y group by y order by s)
+  from generate_series(1,3) x;
+                            QUERY PLAN                             
+-------------------------------------------------------------------
+ Function Scan on pg_catalog.generate_series x
+   Output: (SubPlan 1)
+   Function Call: generate_series(1, 3)
+   SubPlan 1
+     ->  Sort
+           Output: (sum(($0 + y.y))), y.y
+           Sort Key: (sum(($0 + y.y)))
+           ->  HashAggregate
+                 Output: sum((x.x + y.y)), y.y
+                 ->  Function Scan on pg_catalog.generate_series y
+                       Output: y.y
+                       Function Call: generate_series(1, 3)
+(12 rows)
+
+select array(select sum(x+y) s
+            from generate_series(1,3) y group by y order by s)
+  from generate_series(1,3) x;
+  array  
+---------
+ {2,3,4}
+ {3,4,5}
+ {4,5,6}
+(3 rows)
+
 --
 -- test for bitwise integer aggregates
 --

diff --git a/src/test/regress/sql/aggregates.sql b/src/test/regress/sql/aggregates.sql
index bfda284bf4a27bd77b5b5ffd438629dd487ba6c3..f79e7aeed2bc87e1fbcc88b9ea4eaf16da24e01f 100644 (file)
--- a/src/test/regress/sql/aggregates.sql
+++ b/src/test/regress/sql/aggregates.sql
@@ -86,6 +86,16 @@ select
   (select max((select i.unique2 from tenk1 i where i.unique1 = o.unique1)))
 from tenk1 o;
 
+-- Test handling of Params within aggregate arguments in hashed aggregation.
+-- Per bug report from Jeevan Chalke.
+explain (verbose, costs off)
+select array(select sum(x+y) s
+            from generate_series(1,3) y group by y order by s)
+  from generate_series(1,3) x;
+select array(select sum(x+y) s
+            from generate_series(1,3) y group by y order by s)
+  from generate_series(1,3) x;
+
 --
 -- test for bitwise integer aggregates
 --