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Fix improper repetition of previous results from a hashed aggregate.

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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>
This commit is contained in:
Tom Lane
2016-08-24 14:37:50 -04:00
parent 5cd3864075
commit 2c00fad286
9 changed files with 156 additions and 6 deletions
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1
src/backend/optimizer/plan/createplan.c
View File

@ -5664,6 +5664,7 @@ make_agg(List *tlist, List *qual,
node->grpColIdx = grpColIdx;
node->grpOperators = grpOperators;
node->numGroups = numGroups;
node->aggParams = NULL; /* SS_finalize_plan() will fill this */
node->groupingSets = groupingSets;
node->chain = chain;

48
src/backend/optimizer/plan/subselect.c
View File

@ -82,6 +82,7 @@ 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);
/*
@ -2652,6 +2653,29 @@ 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);
@ -2660,7 +2684,6 @@ 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:
@ -2811,6 +2834,29 @@ 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);
finalize_primnode((Node *) agg->aggfilter, context);
return false; /* there can't be any Aggrefs below here */
}
return expression_tree_walker(node, finalize_agg_primnode,
(void *) context);
}
/*
* SS_make_initplan_output_param - make a Param for an initPlan's output
*