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

diff --git a/src/backend/commands/analyze.c b/src/backend/commands/analyze.c
index 07613c38b5cf4d566a968b7f65067a14c917c159..a7966fff83929c56fd06d26889103bfe259a83c0 100644 (file)
--- a/src/backend/commands/analyze.c
+++ b/src/backend/commands/analyze.c
@@ -100,7 +100,7 @@ static VacAttrStats *examine_attribute(Relation onerel, int attnum,
 static int acquire_sample_rows(Relation onerel, int elevel,
                                HeapTuple *rows, int targrows,
                                double *totalrows, double *totaldeadrows);
-static int compare_rows(const void *a, const void *b);
+static int compare_rows(const void *a, const void *b, void *arg);
 static int acquire_inherited_sample_rows(Relation onerel, int elevel,
                                          HeapTuple *rows, int targrows,
                                          double *totalrows, double *totaldeadrows);
@@ -1306,7 +1306,8 @@ acquire_sample_rows(Relation onerel, int elevel,
     * tuples are already sorted.
     */
    if (numrows == targrows)
-       qsort((void *) rows, numrows, sizeof(HeapTuple), compare_rows);
+       qsort_interruptible((void *) rows, numrows, sizeof(HeapTuple),
+                           compare_rows, NULL);
 
    /*
     * Estimate total numbers of live and dead rows in relation, extrapolating
@@ -1342,10 +1343,10 @@ acquire_sample_rows(Relation onerel, int elevel,
 }
 
 /*
- * qsort comparator for sorting rows[] array
+ * Comparator for sorting rows[] array
  */
 static int
-compare_rows(const void *a, const void *b)
+compare_rows(const void *a, const void *b, void *arg)
 {
    HeapTuple   ha = *(const HeapTuple *) a;
    HeapTuple   hb = *(const HeapTuple *) b;
@@ -1836,7 +1837,7 @@ static void compute_scalar_stats(VacAttrStatsP stats,
                                 int samplerows,
                                 double totalrows);
 static int compare_scalars(const void *a, const void *b, void *arg);
-static int compare_mcvs(const void *a, const void *b);
+static int compare_mcvs(const void *a, const void *b, void *arg);
 static int analyze_mcv_list(int *mcv_counts,
                             int num_mcv,
                             double stadistinct,
@@ -2473,8 +2474,8 @@ compute_scalar_stats(VacAttrStatsP stats,
        /* Sort the collected values */
        cxt.ssup = &ssup;
        cxt.tupnoLink = tupnoLink;
-       qsort_arg((void *) values, values_cnt, sizeof(ScalarItem),
-                 compare_scalars, (void *) &cxt);
+       qsort_interruptible((void *) values, values_cnt, sizeof(ScalarItem),
+                           compare_scalars, (void *) &cxt);
 
        /*
         * Now scan the values in order, find the most common ones, and also
@@ -2718,8 +2719,8 @@ compute_scalar_stats(VacAttrStatsP stats,
                        deltafrac;
 
            /* Sort the MCV items into position order to speed next loop */
-           qsort((void *) track, num_mcv,
-                 sizeof(ScalarMCVItem), compare_mcvs);
+           qsort_interruptible((void *) track, num_mcv, sizeof(ScalarMCVItem),
+                               compare_mcvs, NULL);
 
            /*
             * Collapse out the MCV items from the values[] array.
@@ -2882,7 +2883,7 @@ compute_scalar_stats(VacAttrStatsP stats,
 }
 
 /*
- * qsort_arg comparator for sorting ScalarItems
+ * Comparator for sorting ScalarItems
  *
  * Aside from sorting the items, we update the tupnoLink[] array
  * whenever two ScalarItems are found to contain equal datums.  The array
@@ -2919,10 +2920,10 @@ compare_scalars(const void *a, const void *b, void *arg)
 }
 
 /*
- * qsort comparator for sorting ScalarMCVItems by position
+ * Comparator for sorting ScalarMCVItems by position
  */
 static int
-compare_mcvs(const void *a, const void *b)
+compare_mcvs(const void *a, const void *b, void *arg)
 {
    int         da = ((const ScalarMCVItem *) a)->first;
    int         db = ((const ScalarMCVItem *) b)->first;

diff --git a/src/backend/statistics/extended_stats.c b/src/backend/statistics/extended_stats.c
index 7c02fb279ff3a118409dbadd76e2af5ea5f27cc1..d2aa8d0ca3f88a8519aef57a56dee5990c50a9f2 100644 (file)
--- a/src/backend/statistics/extended_stats.c
+++ b/src/backend/statistics/extended_stats.c
@@ -1129,8 +1129,8 @@ build_sorted_items(StatsBuildData *data, int *nitems,
    }
 
    /* do the sort, using the multi-sort */
-   qsort_arg((void *) items, nrows, sizeof(SortItem),
-             multi_sort_compare, mss);
+   qsort_interruptible((void *) items, nrows, sizeof(SortItem),
+                       multi_sort_compare, mss);
 
    return items;
 }

diff --git a/src/backend/statistics/mcv.c b/src/backend/statistics/mcv.c
index 1ef303442854d2de907ce7aa7f821a090e2f3f8f..f10642df4f709fb84911c3e85a9aad5454a1d4ae 100644 (file)
--- 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

diff --git a/src/backend/statistics/mvdistinct.c b/src/backend/statistics/mvdistinct.c
index 6ade5eff78c227cb44787a9d1e798651e6a07836..9b216af517fd886b57f1a0eb97ac58482c868c38 100644 (file)
--- a/src/backend/statistics/mvdistinct.c
+++ b/src/backend/statistics/mvdistinct.c
@@ -489,8 +489,8 @@ 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 */
 

diff --git a/src/backend/tsearch/ts_typanalyze.c b/src/backend/tsearch/ts_typanalyze.c
index 3e1a61b56dba1fd2c70ca4fb699f30d8342be8a5..e771a7cd62d190fec3f5e40cc2ce1547a1899e17 100644 (file)
--- 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;

diff --git a/src/backend/utils/adt/array_typanalyze.c b/src/backend/utils/adt/array_typanalyze.c
index ab1d69b2f4e7c78f8a492f7d9c742ede7ec0be53..1964cedd93ff6890889f5c452bae12ecb03aa631 100644 (file)
--- a/src/backend/utils/adt/array_typanalyze.c
+++ b/src/backend/utils/adt/array_typanalyze.c
@@ -86,9 +86,9 @@ static void prune_element_hashtable(HTAB *elements_tab, int b_current);
 static uint32 element_hash(const void *key, Size keysize);
 static int element_match(const void *key1, const void *key2, Size keysize);
 static int element_compare(const void *key1, const void *key2);
-static int trackitem_compare_frequencies_desc(const void *e1, const void *e2);
-static int trackitem_compare_element(const void *e1, const void *e2);
-static int countitem_compare_count(const void *e1, const void *e2);
+static int trackitem_compare_frequencies_desc(const void *e1, const void *e2, void *arg);
+static int trackitem_compare_element(const void *e1, const void *e2, void *arg);
+static int countitem_compare_count(const void *e1, const void *e2, void *arg);
 
 
 /*
@@ -502,8 +502,8 @@ compute_array_stats(VacAttrStats *stats, AnalyzeAttrFetchFunc fetchfunc,
         */
        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;
        }
@@ -522,8 +522,8 @@ compute_array_stats(VacAttrStats *stats, AnalyzeAttrFetchFunc fetchfunc,
             * the element type's default comparison function.  This permits
             * fast binary searches in selectivity estimation functions.
             */
-           qsort(sort_table, num_mcelem, sizeof(TrackItem *),
-                 trackitem_compare_element);
+           qsort_interruptible(sort_table, num_mcelem, sizeof(TrackItem *),
+                               trackitem_compare_element, NULL);
 
            /* Must copy the target values into anl_context */
            old_context = MemoryContextSwitchTo(stats->anl_context);
@@ -599,8 +599,9 @@ compute_array_stats(VacAttrStats *stats, AnalyzeAttrFetchFunc fetchfunc,
            {
                sorted_count_items[j++] = count_item;
            }
-           qsort(sorted_count_items, count_items_count,
-                 sizeof(DECountItem *), countitem_compare_count);
+           qsort_interruptible(sorted_count_items, count_items_count,
+                               sizeof(DECountItem *),
+                               countitem_compare_count, NULL);
 
            /*
             * Prepare to fill stanumbers with the histogram, followed by the
@@ -751,10 +752,10 @@ element_compare(const void *key1, const void *key2)
 }
 
 /*
- * qsort() comparator for sorting TrackItems by frequencies (descending sort)
+ * Comparator for sorting TrackItems by 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;
@@ -763,10 +764,10 @@ trackitem_compare_frequencies_desc(const void *e1, const void *e2)
 }
 
 /*
- * qsort() comparator for sorting TrackItems by element values
+ * Comparator for sorting TrackItems by element values
  */
 static int
-trackitem_compare_element(const void *e1, const void *e2)
+trackitem_compare_element(const void *e1, const void *e2, void *arg)
 {
    const TrackItem *const *t1 = (const TrackItem *const *) e1;
    const TrackItem *const *t2 = (const TrackItem *const *) e2;
@@ -775,10 +776,10 @@ trackitem_compare_element(const void *e1, const void *e2)
 }
 
 /*
- * qsort() comparator for sorting DECountItems by count
+ * Comparator for sorting DECountItems by count
  */
 static int
-countitem_compare_count(const void *e1, const void *e2)
+countitem_compare_count(const void *e1, const void *e2, void *arg)
 {
    const DECountItem *const *t1 = (const DECountItem *const *) e1;
    const DECountItem *const *t2 = (const DECountItem *const *) e2;

diff --git a/src/backend/utils/adt/rangetypes_typanalyze.c b/src/backend/utils/adt/rangetypes_typanalyze.c
index 2b77e03449a8657a1f30d970cd96a13d3ba7ce62..2043d3f98be434f7ef730bb92a5d13a7a1c82d21 100644 (file)
--- a/src/backend/utils/adt/rangetypes_typanalyze.c
+++ b/src/backend/utils/adt/rangetypes_typanalyze.c
@@ -32,7 +32,7 @@
 #include "utils/rangetypes.h"
 #include "utils/multirangetypes.h"
 
-static int float8_qsort_cmp(const void *a1, const void *a2);
+static int float8_qsort_cmp(const void *a1, const void *a2, void *arg);
 static int range_bound_qsort_cmp(const void *a1, const void *a2, void *arg);
 static void compute_range_stats(VacAttrStats *stats,
                                AnalyzeAttrFetchFunc fetchfunc, int samplerows,
@@ -93,7 +93,7 @@ multirange_typanalyze(PG_FUNCTION_ARGS)
  * Comparison function for sorting float8s, used for range lengths.
  */
 static int
-float8_qsort_cmp(const void *a1, const void *a2)
+float8_qsort_cmp(const void *a1, const void *a2, void *arg)
 {
    const float8 *f1 = (const float8 *) a1;
    const float8 *f2 = (const float8 *) a2;
@@ -280,10 +280,10 @@ compute_range_stats(VacAttrStats *stats, AnalyzeAttrFetchFunc fetchfunc,
        if (non_empty_cnt >= 2)
        {
            /* Sort bound values */
-           qsort_arg(lowers, non_empty_cnt, sizeof(RangeBound),
-                     range_bound_qsort_cmp, typcache);
-           qsort_arg(uppers, non_empty_cnt, sizeof(RangeBound),
-                     range_bound_qsort_cmp, typcache);
+           qsort_interruptible(lowers, non_empty_cnt, sizeof(RangeBound),
+                               range_bound_qsort_cmp, typcache);
+           qsort_interruptible(uppers, non_empty_cnt, sizeof(RangeBound),
+                               range_bound_qsort_cmp, typcache);
 
            num_hist = non_empty_cnt;
            if (num_hist > num_bins)
@@ -345,7 +345,8 @@ compute_range_stats(VacAttrStats *stats, AnalyzeAttrFetchFunc fetchfunc,
             * Ascending sort of range lengths for further filling of
             * histogram
             */
-           qsort(lengths, non_empty_cnt, sizeof(float8), float8_qsort_cmp);
+           qsort_interruptible(lengths, non_empty_cnt, sizeof(float8),
+                               float8_qsort_cmp, NULL);
 
            num_hist = non_empty_cnt;
            if (num_hist > num_bins)

diff --git a/src/backend/utils/sort/Makefile b/src/backend/utils/sort/Makefile
index 26f65fcaf7ad78ddf3f12e1db0e9215ef02fd279..2c31fd453d606c738656ffaf97f0017e2d372662 100644 (file)
--- a/src/backend/utils/sort/Makefile
+++ b/src/backend/utils/sort/Makefile
@@ -16,6 +16,7 @@ override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS)
 
 OBJS = \
    logtape.o \
+   qsort_interruptible.o \
    sharedtuplestore.o \
    sortsupport.o \
    tuplesort.o \

diff --git a/src/backend/utils/sort/qsort_interruptible.c b/src/backend/utils/sort/qsort_interruptible.c
new file mode 100644 (file)
index 0000000..f179b25
--- /dev/null
+++ b/src/backend/utils/sort/qsort_interruptible.c
@@ -0,0 +1,16 @@
+/*
+ * qsort_interruptible.c: qsort_arg that includes CHECK_FOR_INTERRUPTS
+ */
+
+#include "postgres.h"
+#include "miscadmin.h"
+
+#define ST_SORT qsort_interruptible
+#define ST_ELEMENT_TYPE_VOID
+#define ST_COMPARATOR_TYPE_NAME qsort_arg_comparator
+#define ST_COMPARE_RUNTIME_POINTER
+#define ST_COMPARE_ARG_TYPE void
+#define ST_SCOPE
+#define ST_DEFINE
+#define ST_CHECK_FOR_INTERRUPTS
+#include "lib/sort_template.h"

diff --git a/src/include/port.h b/src/include/port.h
index 12c05b5d9f904d7f967e1a9f133ca9af84ccf2c7..e647f62b779d9b55ce99832a8c8697b224719070 100644 (file)
--- 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 *),