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Fix oversized memory allocation in Parallel Hash Join

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During the calculations of the maximum for the number of buckets, take into
account that later we round that to the next power of 2.

Reported-by: Karen Talarico
Bug: #16925
Discussion: https://postgr.es/m/16925-ec96d83529d0d629%40postgresql.org
Author: Thomas Munro, Andrei Lepikhov, Alexander Korotkov
Reviewed-by: Alena Rybakina
Backpatch-through: 12
This commit is contained in:
Alexander Korotkov 2024-01-07 09:03:55 +02:00
parent 37c5516633
commit 714a987bc1
1 changed files with 10 additions and 2 deletions
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12
src/backend/executor/nodeHash.c
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@ -1160,6 +1160,7 @@ ExecParallelHashIncreaseNumBatches(HashJoinTable hashtable)
double dtuples;
double dbuckets;
int new_nbuckets;
uint32 max_buckets;
/*
* We probably also need a smaller bucket array. How many
@ -1172,9 +1173,16 @@ ExecParallelHashIncreaseNumBatches(HashJoinTable hashtable)
* array.
*/
dtuples = (old_batch0->ntuples * 2.0) / new_nbatch;
/*
* We need to calculate the maximum number of buckets to
* stay within the MaxAllocSize boundary. Round the
* maximum number to the previous power of 2 given that
* later we round the number to the next power of 2.
*/
max_buckets = pg_prevpower2_32((uint32)
(MaxAllocSize / sizeof(dsa_pointer_atomic)));
dbuckets = ceil(dtuples / NTUP_PER_BUCKET);
dbuckets = Min(dbuckets,
MaxAllocSize / sizeof(dsa_pointer_atomic));
dbuckets = Min(dbuckets, max_buckets);
new_nbuckets = (int) dbuckets;
new_nbuckets = Max(new_nbuckets, 1024);
new_nbuckets = pg_nextpower2_32(new_nbuckets);