pgsql: Avoid misbehavior when hash_table_bytes < bucket_size.

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

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/1dfc9193af7ff3cde963aa153e21fadbfebe030a

Modified Files
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src/backend/executor/nodeHash.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)