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_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/72d5b27763a86c1d9af79e3169aef885b79373a3

Modified Files
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src/backend/executor/nodeHash.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)