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Commit72d5b27

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Fix oversized memory allocation in Parallel Hash Join
During the calculations of the maximum for the number of buckets, take intoaccount that later we round that to the next power of 2.Reported-by: Karen TalaricoBug: #16925Discussion:https://postgr.es/m/16925-ec96d83529d0d629%40postgresql.orgAuthor: Thomas Munro, Andrei Lepikhov, Alexander KorotkovReviewed-by: Alena RybakinaBackpatch-through: 12
1 parent49fa183 commit72d5b27

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‎src/backend/executor/nodeHash.c‎

Lines changed: 11 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1141,6 +1141,7 @@ ExecParallelHashIncreaseNumBatches(HashJoinTable hashtable)
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doubledtuples;
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doubledbuckets;
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intnew_nbuckets;
1144+
uint32max_buckets;
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/*
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* We probably also need a smaller bucket array. How many
@@ -1153,9 +1154,17 @@ ExecParallelHashIncreaseNumBatches(HashJoinTable hashtable)
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* array.
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*/
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dtuples= (old_batch0->ntuples*2.0) /new_nbatch;
1157+
/*
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* We need to calculate the maximum number of buckets to
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* stay within the MaxAllocSize boundary. Round the
1160+
* maximum number to the previous power of 2 given that
1161+
* later we round the number to the next power of 2.
1162+
*/
1163+
max_buckets=MaxAllocSize /sizeof(dsa_pointer_atomic);
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if ((max_buckets& (max_buckets-1))!=0)
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max_buckets=1 << (my_log2(max_buckets)-1);
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dbuckets=ceil(dtuples /NTUP_PER_BUCKET);
1157-
dbuckets=Min(dbuckets,
1158-
MaxAllocSize /sizeof(dsa_pointer_atomic));
1167+
dbuckets=Min(dbuckets,max_buckets);
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new_nbuckets= (int)dbuckets;
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new_nbuckets=Max(new_nbuckets,1024);
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new_nbuckets=1 <<my_log2(new_nbuckets);

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