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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2022-07-12 16:30:36 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2022-07-12 16:30:36 -0400 |
| commit | e64cdab003027acef29e713087fb667e2319f679 (patch) | |
| tree | 70f558736a70f872f201e278bd4400ba8c1d2b15 /src/backend/statistics/mcv.c | |
| parent | 920072339f304a7da0b5de966117420c96ad78cb (diff) | |
| download | postgresql-e64cdab003027acef29e713087fb667e2319f679.tar.gz postgresql-e64cdab003027acef29e713087fb667e2319f679.zip | |
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
Diffstat (limited to 'src/backend/statistics/mcv.c')
| -rw-r--r-- | src/backend/statistics/mcv.c | 14 |
1 files changed, 7 insertions, 7 deletions
diff --git a/src/backend/statistics/mcv.c b/src/backend/statistics/mcv.c index 1ef30344285..f10642df4f7 100644 --- a/src/backend/statistics/mcv.c +++ b/src/backend/statistics/mcv.c @@ -404,7 +404,7 @@ count_distinct_groups(int numrows, SortItem *items, MultiSortSupport mss) * order. */ static int -compare_sort_item_count(const void *a, const void *b) +compare_sort_item_count(const void *a, const void *b, void *arg) { SortItem *ia = (SortItem *) a; SortItem *ib = (SortItem *) b; @@ -457,8 +457,8 @@ build_distinct_groups(int numrows, SortItem *items, MultiSortSupport mss, Assert(j + 1 == ngroups); /* Sort the distinct groups by frequency (in descending order). */ - pg_qsort((void *) groups, ngroups, sizeof(SortItem), - compare_sort_item_count); + qsort_interruptible((void *) groups, ngroups, sizeof(SortItem), + compare_sort_item_count, NULL); *ndistinct = ngroups; return groups; @@ -528,8 +528,8 @@ build_column_frequencies(SortItem *groups, int ngroups, } /* sort the values, deduplicate */ - qsort_arg((void *) result[dim], ngroups, sizeof(SortItem), - sort_item_compare, ssup); + qsort_interruptible((void *) result[dim], ngroups, sizeof(SortItem), + sort_item_compare, ssup); /* * Identify distinct values, compute frequency (there might be @@ -696,8 +696,8 @@ statext_mcv_serialize(MCVList *mcvlist, VacAttrStats **stats) PrepareSortSupportFromOrderingOp(typentry->lt_opr, &ssup[dim]); - qsort_arg(values[dim], counts[dim], sizeof(Datum), - compare_scalars_simple, &ssup[dim]); + qsort_interruptible(values[dim], counts[dim], sizeof(Datum), + compare_scalars_simple, &ssup[dim]); /* * Walk through the array and eliminate duplicate values, but keep the |