diff options
Diffstat (limited to 'src/backend/optimizer/prep/prepagg.c')
| -rw-r--r-- | src/backend/optimizer/prep/prepagg.c | 28 |
1 files changed, 12 insertions, 16 deletions
diff --git a/src/backend/optimizer/prep/prepagg.c b/src/backend/optimizer/prep/prepagg.c index 89046f9afbb..e1c525760cd 100644 --- a/src/backend/optimizer/prep/prepagg.c +++ b/src/backend/optimizer/prep/prepagg.c @@ -515,28 +515,24 @@ GetAggInitVal(Datum textInitVal, Oid transtype) /* * get_agg_clause_costs - * Recursively find the Aggref nodes in an expression tree, and - * accumulate cost information about them. + * Process the PlannerInfo's 'aggtransinfos' and 'agginfos' lists + * accumulating the cost information about them. * * 'aggsplit' tells us the expected partial-aggregation mode, which affects * the cost estimates. * - * NOTE that the counts/costs are ADDED to those already in *costs ... so - * the caller is responsible for zeroing the struct initially. + * NOTE that the costs are ADDED to those already in *costs ... so the caller + * is responsible for zeroing the struct initially. * - * We count the nodes, estimate their execution costs, and estimate the total - * space needed for their transition state values if all are evaluated in - * parallel (as would be done in a HashAgg plan). Also, we check whether - * partial aggregation is feasible. See AggClauseCosts for the exact set - * of statistics collected. + * For each AggTransInfo, we add the cost of an aggregate transition using + * either the transfn or combinefn depending on the 'aggsplit' value. We also + * account for the costs of any aggfilters and any serializations and + * deserializations of the transition state and also estimate the total space + * needed for the transition states as if each aggregate's state was stored in + * memory concurrently (as would be done in a HashAgg plan). * - * In addition, we mark Aggref nodes with the correct aggtranstype, so - * that that doesn't need to be done repeatedly. (That makes this function's - * name a bit of a misnomer.) - * - * This does not descend into subqueries, and so should be used only after - * reduction of sublinks to subplans, or in contexts where it's known there - * are no subqueries. There mustn't be outer-aggregate references either. + * For each AggInfo in the 'agginfos' list we add the cost of running the + * final function and the direct args, if any. */ void get_agg_clause_costs(PlannerInfo *root, AggSplit aggsplit, AggClauseCosts *costs) |