pgsql: Invent qsort_interruptible().

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

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e64cdab003027acef29e713087fb667e2319f679

Modified Files
--------------
src/backend/commands/analyze.c | 25 ++++++++++-----------
src/backend/statistics/extended_stats.c | 4 ++--
src/backend/statistics/mcv.c | 14 ++++++------
src/backend/statistics/mvdistinct.c | 4 ++--
src/backend/tsearch/ts_typanalyze.c | 22 ++++++++++---------
src/backend/utils/adt/array_typanalyze.c | 31 ++++++++++++++-------------
src/backend/utils/adt/rangetypes_typanalyze.c | 15 +++++++------
src/backend/utils/sort/Makefile | 1 +
src/backend/utils/sort/qsort_interruptible.c | 16 ++++++++++++++
src/include/port.h | 3 +++
10 files changed, 80 insertions(+), 55 deletions(-)