pgsql: Fix oversized memory allocation in Parallel Hash Join

Fix oversized memory allocation in Parallel Hash Join

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

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/714a987bc1333121bb83415f764076c8e7e8d8fb

Modified Files
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src/backend/executor/nodeHash.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)