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Avoid misbehavior when hash_table_bytes < bucket_size.

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It's possible to reach this case when work_mem is very small and tupsize
is (relatively) very large.  In that case ExecChooseHashTableSize would
get an assertion failure, or with asserts off it'd compute nbuckets = 0,
which'd likely cause misbehavior later (I've not checked).  To fix,
clamp the number of buckets to be at least 1.

This is due to faulty conversion of old my_log2() coding in 28d936031.
Back-patch to v13, as that was.

Zhang Mingli

Discussion: https://postgr.es/m/beb64ca0-91e2-44ac-bf4a-7ea36275ec02@Spark
This commit is contained in:
Tom Lane 2022-08-13 16:59:58 -04:00
parent f558088285
commit 55d9cd46f6
1 changed files with 4 additions and 1 deletions
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5
src/backend/executor/nodeHash.c
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@ -832,7 +832,10 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
* overhead for the hash code, pointer to the next tuple, etc.
*/
bucket_size = (tupsize * NTUP_PER_BUCKET + sizeof(HashJoinTuple));
sbuckets = pg_nextpower2_size_t(hash_table_bytes / bucket_size);
if (hash_table_bytes <= bucket_size)
sbuckets = 1; /* avoid pg_nextpower2_size_t(0) */
else
sbuckets = pg_nextpower2_size_t(hash_table_bytes / bucket_size);
sbuckets = Min(sbuckets, max_pointers);
nbuckets = (int) sbuckets;
nbuckets = pg_nextpower2_32(nbuckets);