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_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/1a7c03e6fc75d2a5ee4893252d47f0549f078494

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