From 1a7c03e6fc75d2a5ee4893252d47f0549f078494 Mon Sep 17 00:00:00 2001 From: Alexander Korotkov <akorotkov@postgresql.org> Date: Sun, 7 Jan 2024 09:03:55 +0200 Subject: [PATCH] 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 --- src/backend/executor/nodeHash.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/src/backend/executor/nodeHash.c b/src/backend/executor/nodeHash.c index 59a720db913..aeac4cbf583 100644 --- a/src/backend/executor/nodeHash.c +++ b/src/backend/executor/nodeHash.c @@ -1162,6 +1162,7 @@ ExecParallelHashIncreaseNumBatches(HashJoinTable hashtable) double dtuples; double dbuckets; int new_nbuckets; + uint32 max_buckets; /* * We probably also need a smaller bucket array. How many @@ -1174,9 +1175,16 @@ ExecParallelHashIncreaseNumBatches(HashJoinTable hashtable) * array. */ dtuples = (old_batch0->ntuples * 2.0) / new_nbatch; + /* + * We need to calculate the maximum number of buckets to + * stay within the MaxAllocSize boundary. Round the + * maximum number to the previous power of 2 given that + * later we round the number to the next power of 2. + */ + max_buckets = pg_prevpower2_32((uint32) + (MaxAllocSize / sizeof(dsa_pointer_atomic))); dbuckets = ceil(dtuples / NTUP_PER_BUCKET); - dbuckets = Min(dbuckets, - MaxAllocSize / sizeof(dsa_pointer_atomic)); + dbuckets = Min(dbuckets, max_buckets); new_nbuckets = (int) dbuckets; new_nbuckets = Max(new_nbuckets, 1024); new_nbuckets = pg_nextpower2_32(new_nbuckets);