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Commit7351bfe

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Fix costing for disk-based hash aggregation.
Report and suggestions from Richard Guo and Tomas Vondra.Discussion:https://postgr.es/m/CAMbWs4_W8fYbAn8KxgidAaZHON_Oo08OYn9ze=7remJymLqo5g@mail.gmail.com
1 parent4083f44 commit7351bfe

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2 files changed

+16
-16
lines changed

2 files changed

+16
-16
lines changed

‎src/backend/executor/nodeAgg.c

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1728,6 +1728,8 @@ hash_agg_set_limits(double hashentrysize, uint64 input_groups, int used_bits,
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/* if not expected to spill, use all of work_mem */
17291729
if (input_groups*hashentrysize<work_mem*1024L)
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{
1731+
if (num_partitions!=NULL)
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*num_partitions=0;
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*mem_limit=work_mem*1024L;
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*ngroups_limit=*mem_limit /hashentrysize;
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return;

‎src/backend/optimizer/path/costsize.c

Lines changed: 14 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -2257,14 +2257,15 @@ cost_agg(Path *path, PlannerInfo *root,
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*/
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if (aggstrategy==AGG_HASHED||aggstrategy==AGG_MIXED)
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{
2260+
doublepages;
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doublepages_written=0.0;
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doublepages_read=0.0;
22622263
doublehashentrysize;
22632264
doublenbatches;
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Sizemem_limit;
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uint64ngroups_limit;
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intnum_partitions;
2267-
2268+
intdepth;
22682269

22692270
/*
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* Estimate number of batches based on the computed limits. If less
@@ -2279,25 +2280,22 @@ cost_agg(Path *path, PlannerInfo *root,
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nbatches=Max( (numGroups*hashentrysize) /mem_limit,
22802281
numGroups /ngroups_limit );
22812282

2283+
nbatches=Max(ceil(nbatches),1.0);
2284+
num_partitions=Max(num_partitions,2);
2285+
2286+
/*
2287+
* The number of partitions can change at different levels of
2288+
* recursion; but for the purposes of this calculation assume it stays
2289+
* constant.
2290+
*/
2291+
depth=ceil(log(nbatches) /log(num_partitions) );
2292+
22822293
/*
22832294
* Estimate number of pages read and written. For each level of
22842295
* recursion, a tuple must be written and then later read.
22852296
*/
2286-
if (nbatches>1.0)
2287-
{
2288-
doubledepth;
2289-
doublepages;
2290-
2291-
pages=relation_byte_size(input_tuples,input_width) /BLCKSZ;
2292-
2293-
/*
2294-
* The number of partitions can change at different levels of
2295-
* recursion; but for the purposes of this calculation assume it
2296-
* stays constant.
2297-
*/
2298-
depth=ceil(log(nbatches-1) /log(num_partitions) );
2299-
pages_written=pages_read=pages*depth;
2300-
}
2297+
pages=relation_byte_size(input_tuples,input_width) /BLCKSZ;
2298+
pages_written=pages_read=pages*depth;
23012299

23022300
startup_cost+=pages_written*random_page_cost;
23032301
total_cost+=pages_written*random_page_cost;

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