From 55d9cd46f65a5fc0c3bbb69d36cc9dba597a8c9c Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sat, 13 Aug 2022 16:59:58 -0400 Subject: [PATCH] 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 --- src/backend/executor/nodeHash.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/src/backend/executor/nodeHash.c b/src/backend/executor/nodeHash.c index 123079c16cc..c48d92259f9 100644 --- a/src/backend/executor/nodeHash.c +++ b/src/backend/executor/nodeHash.c @@ -832,7 +832,10 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew, * overhead for the hash code, pointer to the next tuple, etc. */ bucket_size = (tupsize * NTUP_PER_BUCKET + sizeof(HashJoinTuple)); - sbuckets = pg_nextpower2_size_t(hash_table_bytes / bucket_size); + if (hash_table_bytes <= bucket_size) + sbuckets = 1; /* avoid pg_nextpower2_size_t(0) */ + else + sbuckets = pg_nextpower2_size_t(hash_table_bytes / bucket_size); sbuckets = Min(sbuckets, max_pointers); nbuckets = (int) sbuckets; nbuckets = pg_nextpower2_32(nbuckets);