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, 12 insertions, 10 deletions

diff --git a/src/backend/tsearch/ts_typanalyze.c b/src/backend/tsearch/ts_typanalyze.c
index 3e1a61b56db..e771a7cd62d 100644
--- a/src/backend/tsearch/ts_typanalyze.c
+++ b/src/backend/tsearch/ts_typanalyze.c
@@ -44,8 +44,10 @@ static void prune_lexemes_hashtable(HTAB *lexemes_tab, int b_current);
 static uint32 lexeme_hash(const void *key, Size keysize);
 static int	lexeme_match(const void *key1, const void *key2, Size keysize);
 static int	lexeme_compare(const void *key1, const void *key2);
-static int	trackitem_compare_frequencies_desc(const void *e1, const void *e2);
-static int	trackitem_compare_lexemes(const void *e1, const void *e2);
+static int	trackitem_compare_frequencies_desc(const void *e1, const void *e2,
+											   void *arg);
+static int	trackitem_compare_lexemes(const void *e1, const void *e2,
+									  void *arg);
 
 
 /*
@@ -347,8 +349,8 @@ compute_tsvector_stats(VacAttrStats *stats,
 		 */
 		if (num_mcelem < track_len)
 		{
-			qsort(sort_table, track_len, sizeof(TrackItem *),
-				  trackitem_compare_frequencies_desc);
+			qsort_interruptible(sort_table, track_len, sizeof(TrackItem *),
+								trackitem_compare_frequencies_desc, NULL);
 			/* reset minfreq to the smallest frequency we're keeping */
 			minfreq = sort_table[num_mcelem - 1]->frequency;
 		}
@@ -376,8 +378,8 @@ compute_tsvector_stats(VacAttrStats *stats,
 			 * presorted we can employ binary search for that.  See
 			 * ts_selfuncs.c for a real usage scenario.
 			 */
-			qsort(sort_table, num_mcelem, sizeof(TrackItem *),
-				  trackitem_compare_lexemes);
+			qsort_interruptible(sort_table, num_mcelem, sizeof(TrackItem *),
+								trackitem_compare_lexemes, NULL);
 
 			/* Must copy the target values into anl_context */
 			old_context = MemoryContextSwitchTo(stats->anl_context);
@@ -510,10 +512,10 @@ lexeme_compare(const void *key1, const void *key2)
 }
 
 /*
- *	qsort() comparator for sorting TrackItems on frequencies (descending sort)
+ *	Comparator for sorting TrackItems on frequencies (descending sort)
  */
 static int
-trackitem_compare_frequencies_desc(const void *e1, const void *e2)
+trackitem_compare_frequencies_desc(const void *e1, const void *e2, void *arg)
 {
 	const TrackItem *const *t1 = (const TrackItem *const *) e1;
 	const TrackItem *const *t2 = (const TrackItem *const *) e2;
@@ -522,10 +524,10 @@ trackitem_compare_frequencies_desc(const void *e1, const void *e2)
 }
 
 /*
- *	qsort() comparator for sorting TrackItems on lexemes
+ *	Comparator for sorting TrackItems on lexemes
  */
 static int
-trackitem_compare_lexemes(const void *e1, const void *e2)
+trackitem_compare_lexemes(const void *e1, const void *e2, void *arg)
 {
 	const TrackItem *const *t1 = (const TrackItem *const *) e1;
 	const TrackItem *const *t2 = (const TrackItem *const *) e2;