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/[email protected]

1 files changed, 3 insertions, 0 deletions

diff --git a/src/include/port.h b/src/include/port.h
index 12c05b5d9f9..e647f62b779 100644
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -499,6 +499,9 @@ typedef int (*qsort_arg_comparator) (const void *a, const void *b, void *arg);
 extern void qsort_arg(void *base, size_t nel, size_t elsize,
 					  qsort_arg_comparator cmp, void *arg);
 
+extern void qsort_interruptible(void *base, size_t nel, size_t elsize,
+								qsort_arg_comparator cmp, void *arg);
+
 extern void *bsearch_arg(const void *key, const void *base,
 						 size_t nmemb, size_t size,
 						 int (*compar) (const void *, const void *, void *),