From af72b0889441e5ece199f782511d84d72fa6b88c Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Tue, 12 Jul 2022 16:30:36 -0400 Subject: Invent qsort_interruptible(). Justin Pryzby reported that some scenarios could cause gathering of extended statistics to spend many seconds in an un-cancelable qsort() operation. To fix, invent qsort_interruptible(), which is just like qsort_arg() except that it will also do CHECK_FOR_INTERRUPTS every so often. This bloats the backend by a couple of kB, which seems like a good investment. (We considered just enabling CHECK_FOR_INTERRUPTS in the existing qsort and qsort_arg functions, but there are some callers for which that'd demonstrably be unsafe. Opt-in seems like a better way.) For now, just apply qsort_interruptible() in statistics collection. There's probably more places where it could be useful, but we can always change other call sites as we find problems. Back-patch to v14. Before that we didn't have extended stats on expressions, so that the problem was less severe. Also, this patch depends on the sort_template infrastructure introduced in v14. Tom Lane and Justin Pryzby Discussion: https://postgr.es/m/20220509000108.GQ28830@telsasoft.com --- src/backend/statistics/mvdistinct.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'src/backend/statistics/mvdistinct.c') diff --git a/src/backend/statistics/mvdistinct.c b/src/backend/statistics/mvdistinct.c index 4481312d61d..4b4ecec9361 100644 --- a/src/backend/statistics/mvdistinct.c +++ b/src/backend/statistics/mvdistinct.c @@ -488,8 +488,8 @@ ndistinct_for_combination(double totalrows, StatsBuildData *data, } /* We can sort the array now ... */ - qsort_arg((void *) items, numrows, sizeof(SortItem), - multi_sort_compare, mss); + qsort_interruptible((void *) items, numrows, sizeof(SortItem), + multi_sort_compare, mss); /* ... and count the number of distinct combinations */ -- cgit v1.2.3