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Include chunk overhead in hash table entry size estimate.

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Don't try to be precise about it, just use a constant 16 bytes of
chunk overhead. Being smarter would require knowing the memory context
where the chunk will be allocated, which is not known by all callers.

Discussion: https://postgr.es/m/20200325220936.il3ni2fj2j2b45y5@alap3.anarazel.de
This commit is contained in:
Jeff Davis
2020-04-03 19:52:16 -07:00
parent 3e0d80fd8d
commit 0588ee63aa
2 changed files with 31 additions and 7 deletions
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36
src/backend/executor/nodeAgg.c
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@ -297,6 +297,12 @@
/* minimum number of initial hash table buckets */
#define HASHAGG_MIN_BUCKETS 256
/*
* Estimate chunk overhead as a constant 16 bytes. XXX: should this be
* improved?
*/
#define CHUNKHDRSZ 16
/*
* Track all tapes needed for a HashAgg that spills. We don't know the maximum
* number of tapes needed at the start of the algorithm (because it can
@ -1639,14 +1645,32 @@ find_hash_columns(AggState *aggstate)
* Estimate per-hash-table-entry overhead.
*/
Size
hash_agg_entry_size(int numAggs, Size tupleWidth, Size transitionSpace)
hash_agg_entry_size(int numTrans, Size tupleWidth, Size transitionSpace)
{
Size tupleChunkSize;
Size pergroupChunkSize;
Size transitionChunkSize;
Size tupleSize = (MAXALIGN(SizeofMinimalTupleHeader) +
tupleWidth);
Size pergroupSize = numTrans * sizeof(AggStatePerGroupData);
tupleChunkSize = CHUNKHDRSZ + tupleSize;
if (pergroupSize > 0)
pergroupChunkSize = CHUNKHDRSZ + pergroupSize;
else
pergroupChunkSize = 0;
if (transitionSpace > 0)
transitionChunkSize = CHUNKHDRSZ + transitionSpace;
else
transitionChunkSize = 0;
return
MAXALIGN(SizeofMinimalTupleHeader) +
MAXALIGN(tupleWidth) +
MAXALIGN(sizeof(TupleHashEntryData) +
numAggs * sizeof(AggStatePerGroupData)) +
transitionSpace;
sizeof(TupleHashEntryData) +
tupleChunkSize +
pergroupChunkSize +
transitionChunkSize;
}
/*