From 395d943f9fe86289d0831f11ef652f7342bfd792 Mon Sep 17 00:00:00 2001 From: Gregory Hennessy Date: Wed, 16 Jul 2025 20:22:58 -0400 Subject: [PATCH] Change algorithm to use sqrt of buffer size rather than log3 --- src/backend/optimizer/path/allpaths.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c index 6cc6966b060..19e7b30453f 100644 --- a/src/backend/optimizer/path/allpaths.c +++ b/src/backend/optimizer/path/allpaths.c @@ -4273,18 +4273,21 @@ compute_parallel_worker(RelOptInfo *rel, double heap_pages, double index_pages, int heap_parallel_workers = 1; /* - * Select the number of workers based on the log of the size of - * the relation. This probably needs to be a good deal more + * Select the number of workers based on the sqrt of the size of + * the ratio of the heap_pages and the min table scan size. + * This allocates more workers than the previous method based on log3 + * of the ratio. It is easier to make the number of workers smaller with a GUC + * than to make the number larger. + * This probably needs to be a good deal more * sophisticated, but we need something here for now. Note that * the upper limit of the min_parallel_table_scan_size GUC is * chosen to prevent overflow here. */ heap_parallel_threshold = Max(min_parallel_table_scan_size, 1); - while (heap_pages >= (BlockNumber) (heap_parallel_threshold * 3)) + while (heap_pages >= (BlockNumber) (heap_parallel_threshold*heap_parallel_workers*heap_parallel_workers)) { heap_parallel_workers++; - heap_parallel_threshold *= 3; - if (heap_parallel_threshold > INT_MAX / 3) + if (heap_parallel_threshold *heap_parallel_workers*heap_parallel_workers> INT_MAX ) break; /* avoid overflow */ } @@ -4298,11 +4301,10 @@ compute_parallel_worker(RelOptInfo *rel, double heap_pages, double index_pages, /* same calculation as for heap_pages above */ index_parallel_threshold = Max(min_parallel_index_scan_size, 1); - while (index_pages >= (BlockNumber) (index_parallel_threshold * 3)) + while (index_pages >= (BlockNumber) (index_parallel_threshold * index_parallel_workers*index_parallel_workers)) { index_parallel_workers++; - index_parallel_threshold *= 3; - if (index_parallel_threshold > INT_MAX / 3) + if (index_parallel_threshold*index_parallel_workers*index_parallel_workers > INT_MAX) break; /* avoid overflow */ } -- 2.50.1