From c1a619500a41dee654868efe480b0b8a7c67dc4f Mon Sep 17 00:00:00 2001 From: Jeff Davis Date: Mon, 3 Feb 2025 15:13:03 -0800 Subject: [PATCH v2 2/2] Minor refactor of hash_agg_set_limits(). Avoid implicit assumption that input_groups is greater than or equal to one. The assumption appears to be true, but it's easier to read without it. Also, a branch that avoided underflow while calculating a max was hard to read; replace with ssize_t types and a Max(). --- src/backend/executor/nodeAgg.c | 18 ++++++------------ 1 file changed, 6 insertions(+), 12 deletions(-) diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c index 35cf18e5282..fb467ec9877 100644 --- a/src/backend/executor/nodeAgg.c +++ b/src/backend/executor/nodeAgg.c @@ -1809,8 +1809,8 @@ hash_agg_set_limits(double hashentrysize, double input_groups, int used_bits, int *num_partitions) { int npartitions; - Size partition_mem; - Size hash_mem_limit = get_hash_memory_limit(); + ssize_t partition_mem; + ssize_t hash_mem_limit = get_hash_memory_limit(); /* if not expected to spill, use all of hash_mem */ if (input_groups * hashentrysize <= hash_mem_limit) @@ -1818,7 +1818,7 @@ hash_agg_set_limits(double hashentrysize, double input_groups, int used_bits, if (num_partitions != NULL) *num_partitions = 0; *mem_limit = hash_mem_limit; - *ngroups_limit = hash_mem_limit / hashentrysize; + *ngroups_limit = Max(*mem_limit / hashentrysize, 1); return; } @@ -1841,17 +1841,11 @@ hash_agg_set_limits(double hashentrysize, double input_groups, int used_bits, /* * Don't set the limit below 3/4 of hash_mem. In that case, we are at the * minimum number of partitions, so we aren't going to dramatically exceed - * work mem anyway. + * work mem anyway. Use ssize_t to avoid underflow during subtraction. */ - if (hash_mem_limit > 4 * partition_mem) - *mem_limit = hash_mem_limit - partition_mem; - else - *mem_limit = hash_mem_limit * 0.75; + *mem_limit = Max(hash_mem_limit - partition_mem, hash_mem_limit * 0.75); - if (*mem_limit > hashentrysize) - *ngroups_limit = *mem_limit / hashentrysize; - else - *ngroups_limit = 1; + *ngroups_limit = Max(*mem_limit / hashentrysize, 1); } /* -- 2.34.1