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Avoid misbehavior when hash_table_bytes < bucket_size.
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
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@ -832,7 +832,10 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
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* overhead for the hash code, pointer to the next tuple, etc.
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*/
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bucket_size = (tupsize * NTUP_PER_BUCKET + sizeof(HashJoinTuple));
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sbuckets = pg_nextpower2_size_t(hash_table_bytes / bucket_size);
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if (hash_table_bytes <= bucket_size)
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sbuckets = 1; /* avoid pg_nextpower2_size_t(0) */
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else
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sbuckets = pg_nextpower2_size_t(hash_table_bytes / bucket_size);
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sbuckets = Min(sbuckets, max_pointers);
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nbuckets = (int) sbuckets;
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nbuckets = pg_nextpower2_32(nbuckets);
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