Add tests for tuplesort.c.

Previously significant parts of tuplesort.c were untested. This
commit, while not testing every path, significantly increases
coverage.  In particular, this adds tests for abbreviated key logic,
forward/backward scans & scrolling and mark/restore.

I tried to keep the table sizes reasonable, and stress the on-disk
paths by setting work_mem to low values for specific tests. The
buildfarm will tell whether more attention to test time is needed.

Author: Andres Freund
Discussion: https://postgr.es/m/20191013144153.ooxrfglvnaocsrx2@alap3.anarazel.de

src/test/regress/expected/tuplesort.out

@@ -0,0 +1,691 @@
+-- only use parallelism when explicitly intending to do so
+SET max_parallel_maintenance_workers = 0;
+SET max_parallel_workers = 0;
+-- A table with with contents that, when sorted, triggers abbreviated
+-- key aborts. One easy way to achieve that is to use uuids that all
+-- have the same prefix, as abbreviated keys for uuids just use the
+-- first sizeof(Datum) bytes.
+DROP TABLE IF EXISTS abbrev_abort_uuids;
+NOTICE:  table "abbrev_abort_uuids" does not exist, skipping
+CREATE TABLE abbrev_abort_uuids (
+    id serial not null,
+    abort_increasing uuid,
+    abort_decreasing uuid,
+    noabort_increasing uuid,
+    noabort_decreasing uuid);
+INSERT INTO abbrev_abort_uuids (abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing)
+    SELECT
+        ('00000000-0000-0000-0000-'||to_char(g.i, '000000000000FM'))::uuid abort_increasing,
+        ('00000000-0000-0000-0000-'||to_char(20000 - g.i, '000000000000FM'))::uuid abort_decreasing,
+        (to_char(g.i % 10009, '00000000FM')||'-0000-0000-0000-'||to_char(g.i, '000000000000FM'))::uuid noabort_increasing,
+        (to_char(((20000 - g.i) % 10009), '00000000FM')||'-0000-0000-0000-'||to_char(20000 - g.i, '000000000000FM'))::uuid noabort_decreasing
+    FROM generate_series(0, 20000, 1) g(i);
+-- and a few NULLs
+INSERT INTO abbrev_abort_uuids(id) VALUES(0);
+INSERT INTO abbrev_abort_uuids DEFAULT VALUES;
+INSERT INTO abbrev_abort_uuids DEFAULT VALUES;
+-- add just a few duplicates
+INSERT INTO abbrev_abort_uuids (abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing)
+    SELECT abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+    FROM abbrev_abort_uuids
+    WHERE (id < 10 OR id > 19990) AND id % 3 = 0 AND abort_increasing is not null;
+----
+-- Check sort node uses of tuplesort wrt. abbreviated keys
+----
+-- plain sort triggering abbreviated abort
+SELECT abort_increasing, abort_decreasing FROM abbrev_abort_uuids ORDER BY abort_increasing OFFSET 20000 - 4;
+           abort_increasing           |           abort_decreasing           
+--------------------------------------+--------------------------------------
+ 00000000-0000-0000-0000-000000019992 | 00000000-0000-0000-0000-000000000008
+ 00000000-0000-0000-0000-000000019993 | 00000000-0000-0000-0000-000000000007
+ 00000000-0000-0000-0000-000000019994 | 00000000-0000-0000-0000-000000000006
+ 00000000-0000-0000-0000-000000019994 | 00000000-0000-0000-0000-000000000006
+ 00000000-0000-0000-0000-000000019995 | 00000000-0000-0000-0000-000000000005
+ 00000000-0000-0000-0000-000000019996 | 00000000-0000-0000-0000-000000000004
+ 00000000-0000-0000-0000-000000019997 | 00000000-0000-0000-0000-000000000003
+ 00000000-0000-0000-0000-000000019997 | 00000000-0000-0000-0000-000000000003
+ 00000000-0000-0000-0000-000000019998 | 00000000-0000-0000-0000-000000000002
+ 00000000-0000-0000-0000-000000019999 | 00000000-0000-0000-0000-000000000001
+ 00000000-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000
+ 00000000-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000
+                                      | 
+                                      | 
+                                      | 
+(15 rows)
+
+SELECT abort_increasing, abort_decreasing FROM abbrev_abort_uuids ORDER BY abort_decreasing NULLS FIRST OFFSET 20000 - 4;
+           abort_increasing           |           abort_decreasing           
+--------------------------------------+--------------------------------------
+ 00000000-0000-0000-0000-000000000011 | 00000000-0000-0000-0000-000000019989
+ 00000000-0000-0000-0000-000000000010 | 00000000-0000-0000-0000-000000019990
+ 00000000-0000-0000-0000-000000000009 | 00000000-0000-0000-0000-000000019991
+ 00000000-0000-0000-0000-000000000008 | 00000000-0000-0000-0000-000000019992
+ 00000000-0000-0000-0000-000000000008 | 00000000-0000-0000-0000-000000019992
+ 00000000-0000-0000-0000-000000000007 | 00000000-0000-0000-0000-000000019993
+ 00000000-0000-0000-0000-000000000006 | 00000000-0000-0000-0000-000000019994
+ 00000000-0000-0000-0000-000000000005 | 00000000-0000-0000-0000-000000019995
+ 00000000-0000-0000-0000-000000000005 | 00000000-0000-0000-0000-000000019995
+ 00000000-0000-0000-0000-000000000004 | 00000000-0000-0000-0000-000000019996
+ 00000000-0000-0000-0000-000000000003 | 00000000-0000-0000-0000-000000019997
+ 00000000-0000-0000-0000-000000000002 | 00000000-0000-0000-0000-000000019998
+ 00000000-0000-0000-0000-000000000002 | 00000000-0000-0000-0000-000000019998
+ 00000000-0000-0000-0000-000000000001 | 00000000-0000-0000-0000-000000019999
+ 00000000-0000-0000-0000-000000000000 | 00000000-0000-0000-0000-000000020000
+(15 rows)
+
+-- plain sort not triggering abbreviated abort
+SELECT noabort_increasing, noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_increasing OFFSET 20000 - 4;
+          noabort_increasing          |          noabort_decreasing          
+--------------------------------------+--------------------------------------
+ 00009997-0000-0000-0000-000000009997 | 00010003-0000-0000-0000-000000010003
+ 00009998-0000-0000-0000-000000009998 | 00010002-0000-0000-0000-000000010002
+ 00009999-0000-0000-0000-000000009999 | 00010001-0000-0000-0000-000000010001
+ 00010000-0000-0000-0000-000000010000 | 00010000-0000-0000-0000-000000010000
+ 00010001-0000-0000-0000-000000010001 | 00009999-0000-0000-0000-000000009999
+ 00010002-0000-0000-0000-000000010002 | 00009998-0000-0000-0000-000000009998
+ 00010003-0000-0000-0000-000000010003 | 00009997-0000-0000-0000-000000009997
+ 00010004-0000-0000-0000-000000010004 | 00009996-0000-0000-0000-000000009996
+ 00010005-0000-0000-0000-000000010005 | 00009995-0000-0000-0000-000000009995
+ 00010006-0000-0000-0000-000000010006 | 00009994-0000-0000-0000-000000009994
+ 00010007-0000-0000-0000-000000010007 | 00009993-0000-0000-0000-000000009993
+ 00010008-0000-0000-0000-000000010008 | 00009992-0000-0000-0000-000000009992
+                                      | 
+                                      | 
+                                      | 
+(15 rows)
+
+SELECT noabort_increasing, noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing NULLS FIRST OFFSET 20000 - 4;
+          noabort_increasing          |          noabort_decreasing          
+--------------------------------------+--------------------------------------
+ 00010006-0000-0000-0000-000000010006 | 00009994-0000-0000-0000-000000009994
+ 00010005-0000-0000-0000-000000010005 | 00009995-0000-0000-0000-000000009995
+ 00010004-0000-0000-0000-000000010004 | 00009996-0000-0000-0000-000000009996
+ 00010003-0000-0000-0000-000000010003 | 00009997-0000-0000-0000-000000009997
+ 00010002-0000-0000-0000-000000010002 | 00009998-0000-0000-0000-000000009998
+ 00010001-0000-0000-0000-000000010001 | 00009999-0000-0000-0000-000000009999
+ 00010000-0000-0000-0000-000000010000 | 00010000-0000-0000-0000-000000010000
+ 00009999-0000-0000-0000-000000009999 | 00010001-0000-0000-0000-000000010001
+ 00009998-0000-0000-0000-000000009998 | 00010002-0000-0000-0000-000000010002
+ 00009997-0000-0000-0000-000000009997 | 00010003-0000-0000-0000-000000010003
+ 00009996-0000-0000-0000-000000009996 | 00010004-0000-0000-0000-000000010004
+ 00009995-0000-0000-0000-000000009995 | 00010005-0000-0000-0000-000000010005
+ 00009994-0000-0000-0000-000000009994 | 00010006-0000-0000-0000-000000010006
+ 00009993-0000-0000-0000-000000009993 | 00010007-0000-0000-0000-000000010007
+ 00009992-0000-0000-0000-000000009992 | 00010008-0000-0000-0000-000000010008
+(15 rows)
+
+-- bounded sort (disables abbreviated keys)
+SELECT abort_increasing, noabort_increasing FROM abbrev_abort_uuids ORDER BY abort_increasing LIMIT 5;
+           abort_increasing           |          noabort_increasing          
+--------------------------------------+--------------------------------------
+ 00000000-0000-0000-0000-000000000000 | 00000000-0000-0000-0000-000000000000
+ 00000000-0000-0000-0000-000000000001 | 00000001-0000-0000-0000-000000000001
+ 00000000-0000-0000-0000-000000000002 | 00000002-0000-0000-0000-000000000002
+ 00000000-0000-0000-0000-000000000002 | 00000002-0000-0000-0000-000000000002
+ 00000000-0000-0000-0000-000000000003 | 00000003-0000-0000-0000-000000000003
+(5 rows)
+
+SELECT abort_increasing, noabort_increasing FROM abbrev_abort_uuids ORDER BY noabort_increasing NULLS FIRST LIMIT 5;
+           abort_increasing           |          noabort_increasing          
+--------------------------------------+--------------------------------------
+                                      | 
+                                      | 
+                                      | 
+ 00000000-0000-0000-0000-000000000000 | 00000000-0000-0000-0000-000000000000
+ 00000000-0000-0000-0000-000000010009 | 00000000-0000-0000-0000-000000010009
+(5 rows)
+
+----
+-- Check index creation uses of tuplesort wrt. abbreviated keys
+----
+-- index creation using abbreviated keys successfully
+CREATE INDEX abbrev_abort_uuids__noabort_increasing_idx ON abbrev_abort_uuids (noabort_increasing);
+CREATE INDEX abbrev_abort_uuids__noabort_decreasing_idx ON abbrev_abort_uuids (noabort_decreasing);
+-- verify
+EXPLAIN (COSTS OFF)
+SELECT id, noabort_increasing, noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_increasing LIMIT 5;
+                                       QUERY PLAN                                        
+-----------------------------------------------------------------------------------------
+ Limit
+   ->  Index Scan using abbrev_abort_uuids__noabort_increasing_idx on abbrev_abort_uuids
+(2 rows)
+
+SELECT id, noabort_increasing, noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_increasing LIMIT 5;
+  id   |          noabort_increasing          |          noabort_decreasing          
+-------+--------------------------------------+--------------------------------------
+     1 | 00000000-0000-0000-0000-000000000000 | 00009991-0000-0000-0000-000000020000
+ 10010 | 00000000-0000-0000-0000-000000010009 | 00009991-0000-0000-0000-000000009991
+     2 | 00000001-0000-0000-0000-000000000001 | 00009990-0000-0000-0000-000000019999
+ 10011 | 00000001-0000-0000-0000-000000010010 | 00009990-0000-0000-0000-000000009990
+     3 | 00000002-0000-0000-0000-000000000002 | 00009989-0000-0000-0000-000000019998
+(5 rows)
+
+EXPLAIN (COSTS OFF)
+SELECT id, noabort_increasing, noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing LIMIT 5;
+                                       QUERY PLAN                                        
+-----------------------------------------------------------------------------------------
+ Limit
+   ->  Index Scan using abbrev_abort_uuids__noabort_decreasing_idx on abbrev_abort_uuids
+(2 rows)
+
+SELECT id, noabort_increasing, noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing LIMIT 5;
+  id   |          noabort_increasing          |          noabort_decreasing          
+-------+--------------------------------------+--------------------------------------
+ 20001 | 00009991-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000
+ 20010 | 00009991-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000
+  9992 | 00009991-0000-0000-0000-000000009991 | 00000000-0000-0000-0000-000000010009
+ 20000 | 00009990-0000-0000-0000-000000019999 | 00000001-0000-0000-0000-000000000001
+  9991 | 00009990-0000-0000-0000-000000009990 | 00000001-0000-0000-0000-000000010010
+(5 rows)
+
+-- index creation using abbreviated keys, hitting abort
+CREATE INDEX abbrev_abort_uuids__abort_increasing_idx ON abbrev_abort_uuids (abort_increasing);
+CREATE INDEX abbrev_abort_uuids__abort_decreasing_idx ON abbrev_abort_uuids (abort_decreasing);
+-- verify
+EXPLAIN (COSTS OFF)
+SELECT id, abort_increasing, abort_decreasing FROM abbrev_abort_uuids ORDER BY abort_increasing LIMIT 5;
+                                      QUERY PLAN                                       
+---------------------------------------------------------------------------------------
+ Limit
+   ->  Index Scan using abbrev_abort_uuids__abort_increasing_idx on abbrev_abort_uuids
+(2 rows)
+
+SELECT id, abort_increasing, abort_decreasing FROM abbrev_abort_uuids ORDER BY abort_increasing LIMIT 5;
+  id   |           abort_increasing           |           abort_decreasing           
+-------+--------------------------------------+--------------------------------------
+     1 | 00000000-0000-0000-0000-000000000000 | 00000000-0000-0000-0000-000000020000
+     2 | 00000000-0000-0000-0000-000000000001 | 00000000-0000-0000-0000-000000019999
+     3 | 00000000-0000-0000-0000-000000000002 | 00000000-0000-0000-0000-000000019998
+ 20004 | 00000000-0000-0000-0000-000000000002 | 00000000-0000-0000-0000-000000019998
+     4 | 00000000-0000-0000-0000-000000000003 | 00000000-0000-0000-0000-000000019997
+(5 rows)
+
+EXPLAIN (COSTS OFF)
+SELECT id, abort_increasing, abort_decreasing FROM abbrev_abort_uuids ORDER BY abort_decreasing LIMIT 5;
+                                      QUERY PLAN                                       
+---------------------------------------------------------------------------------------
+ Limit
+   ->  Index Scan using abbrev_abort_uuids__abort_decreasing_idx on abbrev_abort_uuids
+(2 rows)
+
+SELECT id, abort_increasing, abort_decreasing FROM abbrev_abort_uuids ORDER BY abort_decreasing LIMIT 5;
+  id   |           abort_increasing           |           abort_decreasing           
+-------+--------------------------------------+--------------------------------------
+ 20001 | 00000000-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000
+ 20010 | 00000000-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000
+ 20000 | 00000000-0000-0000-0000-000000019999 | 00000000-0000-0000-0000-000000000001
+ 19999 | 00000000-0000-0000-0000-000000019998 | 00000000-0000-0000-0000-000000000002
+ 19998 | 00000000-0000-0000-0000-000000019997 | 00000000-0000-0000-0000-000000000003
+(5 rows)
+
+----
+-- Check CLUSTER uses of tuplesort wrt. abbreviated keys
+----
+-- when aborting, increasing order
+BEGIN;
+SET LOCAL enable_indexscan = false;
+CLUSTER abbrev_abort_uuids USING abbrev_abort_uuids__abort_increasing_idx;
+-- head
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid LIMIT 5;
+  id   |           abort_increasing           |           abort_decreasing           |          noabort_increasing          |          noabort_decreasing          
+-------+--------------------------------------+--------------------------------------+--------------------------------------+--------------------------------------
+     1 | 00000000-0000-0000-0000-000000000000 | 00000000-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000 | 00009991-0000-0000-0000-000000020000
+     2 | 00000000-0000-0000-0000-000000000001 | 00000000-0000-0000-0000-000000019999 | 00000001-0000-0000-0000-000000000001 | 00009990-0000-0000-0000-000000019999
+     3 | 00000000-0000-0000-0000-000000000002 | 00000000-0000-0000-0000-000000019998 | 00000002-0000-0000-0000-000000000002 | 00009989-0000-0000-0000-000000019998
+ 20004 | 00000000-0000-0000-0000-000000000002 | 00000000-0000-0000-0000-000000019998 | 00000002-0000-0000-0000-000000000002 | 00009989-0000-0000-0000-000000019998
+     4 | 00000000-0000-0000-0000-000000000003 | 00000000-0000-0000-0000-000000019997 | 00000003-0000-0000-0000-000000000003 | 00009988-0000-0000-0000-000000019997
+(5 rows)
+
+-- tail
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid DESC LIMIT 5;
+  id   |           abort_increasing           |           abort_decreasing           |          noabort_increasing          |          noabort_decreasing          
+-------+--------------------------------------+--------------------------------------+--------------------------------------+--------------------------------------
+     0 |                                      |                                      |                                      | 
+ 20002 |                                      |                                      |                                      | 
+ 20003 |                                      |                                      |                                      | 
+ 20001 | 00000000-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000 | 00009991-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000
+ 20010 | 00000000-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000 | 00009991-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000
+(5 rows)
+
+ROLLBACK;
+-- when aborting, decreasing order
+BEGIN;
+SET LOCAL enable_indexscan = false;
+CLUSTER abbrev_abort_uuids USING abbrev_abort_uuids__abort_decreasing_idx;
+-- head
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid LIMIT 5;
+  id   |           abort_increasing           |           abort_decreasing           |          noabort_increasing          |          noabort_decreasing          
+-------+--------------------------------------+--------------------------------------+--------------------------------------+--------------------------------------
+ 20010 | 00000000-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000 | 00009991-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000
+ 20001 | 00000000-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000 | 00009991-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000
+ 20000 | 00000000-0000-0000-0000-000000019999 | 00000000-0000-0000-0000-000000000001 | 00009990-0000-0000-0000-000000019999 | 00000001-0000-0000-0000-000000000001
+ 19999 | 00000000-0000-0000-0000-000000019998 | 00000000-0000-0000-0000-000000000002 | 00009989-0000-0000-0000-000000019998 | 00000002-0000-0000-0000-000000000002
+ 20009 | 00000000-0000-0000-0000-000000019997 | 00000000-0000-0000-0000-000000000003 | 00009988-0000-0000-0000-000000019997 | 00000003-0000-0000-0000-000000000003
+(5 rows)
+
+-- tail
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid DESC LIMIT 5;
+  id   |           abort_increasing           |           abort_decreasing           |          noabort_increasing          |          noabort_decreasing          
+-------+--------------------------------------+--------------------------------------+--------------------------------------+--------------------------------------
+     0 |                                      |                                      |                                      | 
+ 20002 |                                      |                                      |                                      | 
+ 20003 |                                      |                                      |                                      | 
+     1 | 00000000-0000-0000-0000-000000000000 | 00000000-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000 | 00009991-0000-0000-0000-000000020000
+     2 | 00000000-0000-0000-0000-000000000001 | 00000000-0000-0000-0000-000000019999 | 00000001-0000-0000-0000-000000000001 | 00009990-0000-0000-0000-000000019999
+(5 rows)
+
+ROLLBACK;
+-- when not aborting, increasing order
+BEGIN;
+SET LOCAL enable_indexscan = false;
+CLUSTER abbrev_abort_uuids USING abbrev_abort_uuids__noabort_increasing_idx;
+-- head
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid LIMIT 5;
+  id   |           abort_increasing           |           abort_decreasing           |          noabort_increasing          |          noabort_decreasing          
+-------+--------------------------------------+--------------------------------------+--------------------------------------+--------------------------------------
+     1 | 00000000-0000-0000-0000-000000000000 | 00000000-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000 | 00009991-0000-0000-0000-000000020000
+ 10010 | 00000000-0000-0000-0000-000000010009 | 00000000-0000-0000-0000-000000009991 | 00000000-0000-0000-0000-000000010009 | 00009991-0000-0000-0000-000000009991
+     2 | 00000000-0000-0000-0000-000000000001 | 00000000-0000-0000-0000-000000019999 | 00000001-0000-0000-0000-000000000001 | 00009990-0000-0000-0000-000000019999
+ 10011 | 00000000-0000-0000-0000-000000010010 | 00000000-0000-0000-0000-000000009990 | 00000001-0000-0000-0000-000000010010 | 00009990-0000-0000-0000-000000009990
+ 20004 | 00000000-0000-0000-0000-000000000002 | 00000000-0000-0000-0000-000000019998 | 00000002-0000-0000-0000-000000000002 | 00009989-0000-0000-0000-000000019998
+(5 rows)
+
+-- tail
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid DESC LIMIT 5;
+  id   |           abort_increasing           |           abort_decreasing           |          noabort_increasing          |          noabort_decreasing          
+-------+--------------------------------------+--------------------------------------+--------------------------------------+--------------------------------------
+     0 |                                      |                                      |                                      | 
+ 20002 |                                      |                                      |                                      | 
+ 20003 |                                      |                                      |                                      | 
+ 10009 | 00000000-0000-0000-0000-000000010008 | 00000000-0000-0000-0000-000000009992 | 00010008-0000-0000-0000-000000010008 | 00009992-0000-0000-0000-000000009992
+ 10008 | 00000000-0000-0000-0000-000000010007 | 00000000-0000-0000-0000-000000009993 | 00010007-0000-0000-0000-000000010007 | 00009993-0000-0000-0000-000000009993
+(5 rows)
+
+ROLLBACK;
+-- when no aborting, decreasing order
+BEGIN;
+SET LOCAL enable_indexscan = false;
+CLUSTER abbrev_abort_uuids USING abbrev_abort_uuids__noabort_decreasing_idx;
+-- head
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid LIMIT 5;
+  id   |           abort_increasing           |           abort_decreasing           |          noabort_increasing          |          noabort_decreasing          
+-------+--------------------------------------+--------------------------------------+--------------------------------------+--------------------------------------
+ 20010 | 00000000-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000 | 00009991-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000
+ 20001 | 00000000-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000 | 00009991-0000-0000-0000-000000020000 | 00000000-0000-0000-0000-000000000000
+  9992 | 00000000-0000-0000-0000-000000009991 | 00000000-0000-0000-0000-000000010009 | 00009991-0000-0000-0000-000000009991 | 00000000-0000-0000-0000-000000010009
+ 20000 | 00000000-0000-0000-0000-000000019999 | 00000000-0000-0000-0000-000000000001 | 00009990-0000-0000-0000-000000019999 | 00000001-0000-0000-0000-000000000001
+  9991 | 00000000-0000-0000-0000-000000009990 | 00000000-0000-0000-0000-000000010010 | 00009990-0000-0000-0000-000000009990 | 00000001-0000-0000-0000-000000010010
+(5 rows)
+
+-- tail
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid DESC LIMIT 5;
+  id   |           abort_increasing           |           abort_decreasing           |          noabort_increasing          |          noabort_decreasing          
+-------+--------------------------------------+--------------------------------------+--------------------------------------+--------------------------------------
+     0 |                                      |                                      |                                      | 
+ 20003 |                                      |                                      |                                      | 
+ 20002 |                                      |                                      |                                      | 
+  9993 | 00000000-0000-0000-0000-000000009992 | 00000000-0000-0000-0000-000000010008 | 00009992-0000-0000-0000-000000009992 | 00010008-0000-0000-0000-000000010008
+  9994 | 00000000-0000-0000-0000-000000009993 | 00000000-0000-0000-0000-000000010007 | 00009993-0000-0000-0000-000000009993 | 00010007-0000-0000-0000-000000010007
+(5 rows)
+
+ROLLBACK;
+----
+-- test forward and backward scans for in-memory and disk based tuplesort
+----
+-- in-memory
+BEGIN;
+SET LOCAL enable_indexscan = false;
+-- unfortunately can't show analyze output confirming sort method,
+-- the memory used output wouldn't be stable
+EXPLAIN (COSTS OFF) DECLARE c SCROLL CURSOR FOR SELECT noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing;
+              QUERY PLAN              
+--------------------------------------
+ Sort
+   Sort Key: noabort_decreasing
+   ->  Seq Scan on abbrev_abort_uuids
+(3 rows)
+
+DECLARE c SCROLL CURSOR FOR SELECT noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing;
+-- first and second
+FETCH NEXT FROM c;
+          noabort_decreasing          
+--------------------------------------
+ 00000000-0000-0000-0000-000000000000
+(1 row)
+
+FETCH NEXT FROM c;
+          noabort_decreasing          
+--------------------------------------
+ 00000000-0000-0000-0000-000000000000
+(1 row)
+
+-- scroll beyond beginning
+FETCH BACKWARD FROM c;
+          noabort_decreasing          
+--------------------------------------
+ 00000000-0000-0000-0000-000000000000
+(1 row)
+
+FETCH BACKWARD FROM c;
+ noabort_decreasing 
+--------------------
+(0 rows)
+
+FETCH BACKWARD FROM c;
+ noabort_decreasing 
+--------------------
+(0 rows)
+
+FETCH BACKWARD FROM c;
+ noabort_decreasing 
+--------------------
+(0 rows)
+
+FETCH NEXT FROM c;
+          noabort_decreasing          
+--------------------------------------
+ 00000000-0000-0000-0000-000000000000
+(1 row)
+
+-- scroll beyond end end
+FETCH LAST FROM c;
+ noabort_decreasing 
+--------------------
+ 
+(1 row)
+
+FETCH BACKWARD FROM c;
+ noabort_decreasing 
+--------------------
+ 
+(1 row)
+
+FETCH NEXT FROM c;
+ noabort_decreasing 
+--------------------
+ 
+(1 row)
+
+FETCH NEXT FROM c;
+ noabort_decreasing 
+--------------------
+(0 rows)
+
+FETCH NEXT FROM c;
+ noabort_decreasing 
+--------------------
+(0 rows)
+
+FETCH BACKWARD FROM c;
+ noabort_decreasing 
+--------------------
+ 
+(1 row)
+
+FETCH NEXT FROM c;
+ noabort_decreasing 
+--------------------
+(0 rows)
+
+COMMIT;
+-- disk based
+BEGIN;
+SET LOCAL enable_indexscan = false;
+SET LOCAL work_mem = '100kB';
+-- unfortunately can't show analyze output confirming sort method,
+-- the memory used output wouldn't be stable
+EXPLAIN (COSTS OFF) DECLARE c SCROLL CURSOR FOR SELECT noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing;
+              QUERY PLAN              
+--------------------------------------
+ Sort
+   Sort Key: noabort_decreasing
+   ->  Seq Scan on abbrev_abort_uuids
+(3 rows)
+
+DECLARE c SCROLL CURSOR FOR SELECT noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing;
+-- first and second
+FETCH NEXT FROM c;
+          noabort_decreasing          
+--------------------------------------
+ 00000000-0000-0000-0000-000000000000
+(1 row)
+
+FETCH NEXT FROM c;
+          noabort_decreasing          
+--------------------------------------
+ 00000000-0000-0000-0000-000000000000
+(1 row)
+
+-- scroll beyond beginning
+FETCH BACKWARD FROM c;
+          noabort_decreasing          
+--------------------------------------
+ 00000000-0000-0000-0000-000000000000
+(1 row)
+
+FETCH BACKWARD FROM c;
+ noabort_decreasing 
+--------------------
+(0 rows)
+
+FETCH BACKWARD FROM c;
+ noabort_decreasing 
+--------------------
+(0 rows)
+
+FETCH BACKWARD FROM c;
+ noabort_decreasing 
+--------------------
+(0 rows)
+
+FETCH NEXT FROM c;
+          noabort_decreasing          
+--------------------------------------
+ 00000000-0000-0000-0000-000000000000
+(1 row)
+
+-- scroll beyond end end
+FETCH LAST FROM c;
+ noabort_decreasing 
+--------------------
+ 
+(1 row)
+
+FETCH BACKWARD FROM c;
+ noabort_decreasing 
+--------------------
+ 
+(1 row)
+
+FETCH NEXT FROM c;
+ noabort_decreasing 
+--------------------
+ 
+(1 row)
+
+FETCH NEXT FROM c;
+ noabort_decreasing 
+--------------------
+(0 rows)
+
+FETCH NEXT FROM c;
+ noabort_decreasing 
+--------------------
+(0 rows)
+
+FETCH BACKWARD FROM c;
+ noabort_decreasing 
+--------------------
+ 
+(1 row)
+
+FETCH NEXT FROM c;
+ noabort_decreasing 
+--------------------
+(0 rows)
+
+COMMIT;
+----
+-- test tuplesort using both in-memory and disk sort
+---
+-- memory based
+SELECT
+    -- fixed-width by-value datum
+    (array_agg(id ORDER BY id DESC NULLS FIRST))[0:5],
+    -- fixed-width by-ref datum
+    (array_agg(abort_increasing ORDER BY abort_increasing DESC NULLS LAST))[0:5],
+    -- variable-width datum
+    (array_agg(id::text ORDER BY id::text DESC NULLS LAST))[0:5],
+    -- fixed width by-value datum tuplesort
+    percentile_disc(0.99) WITHIN GROUP (ORDER BY id),
+    -- ensure state is shared
+    percentile_disc(0.01) WITHIN GROUP (ORDER BY id),
+    -- fixed width by-ref datum tuplesort
+    percentile_disc(0.8) WITHIN GROUP (ORDER BY abort_increasing),
+    -- variable width by-ref datum tuplesort
+    percentile_disc(0.2) WITHIN GROUP (ORDER BY id::text),
+    -- multi-column tuplesort
+    rank('00000000-0000-0000-0000-000000000000', '2', '2') WITHIN GROUP (ORDER BY noabort_increasing, id, id::text)
+FROM (
+    SELECT * FROM abbrev_abort_uuids
+    UNION ALL
+    SELECT NULL, NULL, NULL, NULL, NULL) s;
+           array_agg            |                                                                                         array_agg                                                                                          |         array_agg          | percentile_disc | percentile_disc |           percentile_disc            | percentile_disc | rank 
+--------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------+-----------------+-----------------+--------------------------------------+-----------------+------
+ {NULL,20010,20009,20008,20007} | {00000000-0000-0000-0000-000000020000,00000000-0000-0000-0000-000000020000,00000000-0000-0000-0000-000000019999,00000000-0000-0000-0000-000000019998,00000000-0000-0000-0000-000000019997} | {9999,9998,9997,9996,9995} |           19810 |             200 | 00000000-0000-0000-0000-000000016003 | 136             |    2
+(1 row)
+
+-- disk based (see also above)
+BEGIN;
+SET LOCAL work_mem = '100kB';
+SELECT
+    (array_agg(id ORDER BY id DESC NULLS FIRST))[0:5],
+    (array_agg(abort_increasing ORDER BY abort_increasing DESC NULLS LAST))[0:5],
+    (array_agg(id::text ORDER BY id::text DESC NULLS LAST))[0:5],
+    percentile_disc(0.99) WITHIN GROUP (ORDER BY id),
+    percentile_disc(0.01) WITHIN GROUP (ORDER BY id),
+    percentile_disc(0.8) WITHIN GROUP (ORDER BY abort_increasing),
+    percentile_disc(0.2) WITHIN GROUP (ORDER BY id::text),
+    rank('00000000-0000-0000-0000-000000000000', '2', '2') WITHIN GROUP (ORDER BY noabort_increasing, id, id::text)
+FROM (
+    SELECT * FROM abbrev_abort_uuids
+    UNION ALL
+    SELECT NULL, NULL, NULL, NULL, NULL) s;
+           array_agg            |                                                                                         array_agg                                                                                          |         array_agg          | percentile_disc | percentile_disc |           percentile_disc            | percentile_disc | rank 
+--------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------+-----------------+-----------------+--------------------------------------+-----------------+------
+ {NULL,20010,20009,20008,20007} | {00000000-0000-0000-0000-000000020000,00000000-0000-0000-0000-000000020000,00000000-0000-0000-0000-000000019999,00000000-0000-0000-0000-000000019998,00000000-0000-0000-0000-000000019997} | {9999,9998,9997,9996,9995} |           19810 |             200 | 00000000-0000-0000-0000-000000016003 | 136             |    2
+(1 row)
+
+ROLLBACK;
+----
+-- test tuplesort mark/restore
+---
+CREATE TABLE test_mark_restore(col1 int, col2 int, col12 int);
+-- need a few duplicates for mark/restore to matter
+INSERT INTO test_mark_restore(col1, col2, col12)
+   SELECT a.i, b.i, a.i * b.i FROM generate_series(1, 500) a(i), generate_series(1, 5) b(i);
+BEGIN;
+SET LOCAL enable_nestloop = off;
+SET LOCAL enable_hashjoin = off;
+-- set query into variable once, to avoid repetition of the fairly long query
+SELECT $$
+    SELECT col12, count(distinct a.col1), count(distinct a.col2), count(distinct b.col1), count(distinct b.col2), count(*)
+    FROM test_mark_restore a
+        JOIN test_mark_restore b USING(col12)
+    GROUP BY 1
+    HAVING count(*) > 1
+    ORDER BY 2 DESC, 1 DESC, 3 DESC, 4 DESC, 5 DESC, 6 DESC
+    LIMIT 10
+$$ AS qry \gset
+-- test mark/restore with in-memory sorts
+EXPLAIN (COSTS OFF) :qry;
+                                                                                 QUERY PLAN                                                                                  
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Limit
+   ->  Sort
+         Sort Key: (count(DISTINCT a.col1)) DESC, a.col12 DESC, (count(DISTINCT a.col2)) DESC, (count(DISTINCT b.col1)) DESC, (count(DISTINCT b.col2)) DESC, (count(*)) DESC
+         ->  GroupAggregate
+               Group Key: a.col12
+               Filter: (count(*) > 1)
+               ->  Merge Join
+                     Merge Cond: (a.col12 = b.col12)
+                     ->  Sort
+                           Sort Key: a.col12 DESC
+                           ->  Seq Scan on test_mark_restore a
+                     ->  Sort
+                           Sort Key: b.col12 DESC
+                           ->  Seq Scan on test_mark_restore b
+(14 rows)
+
+:qry;
+ col12 | count | count | count | count | count 
+-------+-------+-------+-------+-------+-------
+   480 |     5 |     5 |     5 |     5 |    25
+   420 |     5 |     5 |     5 |     5 |    25
+   360 |     5 |     5 |     5 |     5 |    25
+   300 |     5 |     5 |     5 |     5 |    25
+   240 |     5 |     5 |     5 |     5 |    25
+   180 |     5 |     5 |     5 |     5 |    25
+   120 |     5 |     5 |     5 |     5 |    25
+    60 |     5 |     5 |     5 |     5 |    25
+   960 |     4 |     4 |     4 |     4 |    16
+   900 |     4 |     4 |     4 |     4 |    16
+(10 rows)
+
+-- test mark/restore with on-disk sorts
+SET LOCAL work_mem = '100kB';
+EXPLAIN (COSTS OFF) :qry;
+                                                                                 QUERY PLAN                                                                                  
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Limit
+   ->  Sort
+         Sort Key: (count(DISTINCT a.col1)) DESC, a.col12 DESC, (count(DISTINCT a.col2)) DESC, (count(DISTINCT b.col1)) DESC, (count(DISTINCT b.col2)) DESC, (count(*)) DESC
+         ->  GroupAggregate
+               Group Key: a.col12
+               Filter: (count(*) > 1)
+               ->  Merge Join
+                     Merge Cond: (a.col12 = b.col12)
+                     ->  Sort
+                           Sort Key: a.col12 DESC
+                           ->  Seq Scan on test_mark_restore a
+                     ->  Materialize
+                           ->  Sort
+                                 Sort Key: b.col12 DESC
+                                 ->  Seq Scan on test_mark_restore b
+(15 rows)
+
+:qry;
+ col12 | count | count | count | count | count 
+-------+-------+-------+-------+-------+-------
+   480 |     5 |     5 |     5 |     5 |    25
+   420 |     5 |     5 |     5 |     5 |    25
+   360 |     5 |     5 |     5 |     5 |    25
+   300 |     5 |     5 |     5 |     5 |    25
+   240 |     5 |     5 |     5 |     5 |    25
+   180 |     5 |     5 |     5 |     5 |    25
+   120 |     5 |     5 |     5 |     5 |    25
+    60 |     5 |     5 |     5 |     5 |    25
+   960 |     4 |     4 |     4 |     4 |    16
+   900 |     4 |     4 |     4 |     4 |    16
+(10 rows)
+
+COMMIT;
+-- cleanup
+DROP TABLE IF EXISTS abbrev_abort_uuids;
+DROP TABLE IF EXISTS test_mark_restore;

src/test/regress/parallel_schedule

@@ -112,7 +112,7 @@ test: plancache limit plpgsql copy2 temp domain rangefuncs prepare conversion tr
 # ----------
 # Another group of parallel tests
 # ----------
-test: partition_join partition_prune reloptions hash_part indexing partition_aggregate partition_info
+test: partition_join partition_prune reloptions hash_part indexing partition_aggregate partition_info tuplesort
 
 # event triggers cannot run concurrently with any test that runs DDL
 test: event_trigger

src/test/regress/sql/tuplesort.sql

@@ -0,0 +1,304 @@
+-- only use parallelism when explicitly intending to do so
+SET max_parallel_maintenance_workers = 0;
+SET max_parallel_workers = 0;
+
+-- A table with with contents that, when sorted, triggers abbreviated
+-- key aborts. One easy way to achieve that is to use uuids that all
+-- have the same prefix, as abbreviated keys for uuids just use the
+-- first sizeof(Datum) bytes.
+DROP TABLE IF EXISTS abbrev_abort_uuids;
+
+CREATE TABLE abbrev_abort_uuids (
+    id serial not null,
+    abort_increasing uuid,
+    abort_decreasing uuid,
+    noabort_increasing uuid,
+    noabort_decreasing uuid);
+
+INSERT INTO abbrev_abort_uuids (abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing)
+    SELECT
+        ('00000000-0000-0000-0000-'||to_char(g.i, '000000000000FM'))::uuid abort_increasing,
+        ('00000000-0000-0000-0000-'||to_char(20000 - g.i, '000000000000FM'))::uuid abort_decreasing,
+        (to_char(g.i % 10009, '00000000FM')||'-0000-0000-0000-'||to_char(g.i, '000000000000FM'))::uuid noabort_increasing,
+        (to_char(((20000 - g.i) % 10009), '00000000FM')||'-0000-0000-0000-'||to_char(20000 - g.i, '000000000000FM'))::uuid noabort_decreasing
+    FROM generate_series(0, 20000, 1) g(i);
+
+-- and a few NULLs
+INSERT INTO abbrev_abort_uuids(id) VALUES(0);
+INSERT INTO abbrev_abort_uuids DEFAULT VALUES;
+INSERT INTO abbrev_abort_uuids DEFAULT VALUES;
+
+-- add just a few duplicates
+INSERT INTO abbrev_abort_uuids (abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing)
+    SELECT abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+    FROM abbrev_abort_uuids
+    WHERE (id < 10 OR id > 19990) AND id % 3 = 0 AND abort_increasing is not null;
+
+----
+-- Check sort node uses of tuplesort wrt. abbreviated keys
+----
+
+-- plain sort triggering abbreviated abort
+SELECT abort_increasing, abort_decreasing FROM abbrev_abort_uuids ORDER BY abort_increasing OFFSET 20000 - 4;
+SELECT abort_increasing, abort_decreasing FROM abbrev_abort_uuids ORDER BY abort_decreasing NULLS FIRST OFFSET 20000 - 4;
+
+-- plain sort not triggering abbreviated abort
+SELECT noabort_increasing, noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_increasing OFFSET 20000 - 4;
+SELECT noabort_increasing, noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing NULLS FIRST OFFSET 20000 - 4;
+
+-- bounded sort (disables abbreviated keys)
+SELECT abort_increasing, noabort_increasing FROM abbrev_abort_uuids ORDER BY abort_increasing LIMIT 5;
+SELECT abort_increasing, noabort_increasing FROM abbrev_abort_uuids ORDER BY noabort_increasing NULLS FIRST LIMIT 5;
+
+
+----
+-- Check index creation uses of tuplesort wrt. abbreviated keys
+----
+
+-- index creation using abbreviated keys successfully
+CREATE INDEX abbrev_abort_uuids__noabort_increasing_idx ON abbrev_abort_uuids (noabort_increasing);
+CREATE INDEX abbrev_abort_uuids__noabort_decreasing_idx ON abbrev_abort_uuids (noabort_decreasing);
+
+-- verify
+EXPLAIN (COSTS OFF)
+SELECT id, noabort_increasing, noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_increasing LIMIT 5;
+SELECT id, noabort_increasing, noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_increasing LIMIT 5;
+EXPLAIN (COSTS OFF)
+SELECT id, noabort_increasing, noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing LIMIT 5;
+SELECT id, noabort_increasing, noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing LIMIT 5;
+
+-- index creation using abbreviated keys, hitting abort
+CREATE INDEX abbrev_abort_uuids__abort_increasing_idx ON abbrev_abort_uuids (abort_increasing);
+CREATE INDEX abbrev_abort_uuids__abort_decreasing_idx ON abbrev_abort_uuids (abort_decreasing);
+
+-- verify
+EXPLAIN (COSTS OFF)
+SELECT id, abort_increasing, abort_decreasing FROM abbrev_abort_uuids ORDER BY abort_increasing LIMIT 5;
+SELECT id, abort_increasing, abort_decreasing FROM abbrev_abort_uuids ORDER BY abort_increasing LIMIT 5;
+EXPLAIN (COSTS OFF)
+SELECT id, abort_increasing, abort_decreasing FROM abbrev_abort_uuids ORDER BY abort_decreasing LIMIT 5;
+SELECT id, abort_increasing, abort_decreasing FROM abbrev_abort_uuids ORDER BY abort_decreasing LIMIT 5;
+
+
+----
+-- Check CLUSTER uses of tuplesort wrt. abbreviated keys
+----
+
+-- when aborting, increasing order
+BEGIN;
+SET LOCAL enable_indexscan = false;
+CLUSTER abbrev_abort_uuids USING abbrev_abort_uuids__abort_increasing_idx;
+
+-- head
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid LIMIT 5;
+
+-- tail
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid DESC LIMIT 5;
+ROLLBACK;
+
+-- when aborting, decreasing order
+BEGIN;
+SET LOCAL enable_indexscan = false;
+CLUSTER abbrev_abort_uuids USING abbrev_abort_uuids__abort_decreasing_idx;
+
+-- head
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid LIMIT 5;
+
+-- tail
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid DESC LIMIT 5;
+ROLLBACK;
+
+-- when not aborting, increasing order
+BEGIN;
+SET LOCAL enable_indexscan = false;
+CLUSTER abbrev_abort_uuids USING abbrev_abort_uuids__noabort_increasing_idx;
+
+-- head
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid LIMIT 5;
+
+-- tail
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid DESC LIMIT 5;
+ROLLBACK;
+
+-- when no aborting, decreasing order
+BEGIN;
+SET LOCAL enable_indexscan = false;
+CLUSTER abbrev_abort_uuids USING abbrev_abort_uuids__noabort_decreasing_idx;
+
+-- head
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid LIMIT 5;
+
+-- tail
+SELECT id, abort_increasing, abort_decreasing, noabort_increasing, noabort_decreasing
+FROM abbrev_abort_uuids
+ORDER BY ctid DESC LIMIT 5;
+ROLLBACK;
+
+----
+-- test forward and backward scans for in-memory and disk based tuplesort
+----
+
+-- in-memory
+BEGIN;
+SET LOCAL enable_indexscan = false;
+-- unfortunately can't show analyze output confirming sort method,
+-- the memory used output wouldn't be stable
+EXPLAIN (COSTS OFF) DECLARE c SCROLL CURSOR FOR SELECT noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing;
+DECLARE c SCROLL CURSOR FOR SELECT noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing;
+
+-- first and second
+FETCH NEXT FROM c;
+FETCH NEXT FROM c;
+
+-- scroll beyond beginning
+FETCH BACKWARD FROM c;
+FETCH BACKWARD FROM c;
+FETCH BACKWARD FROM c;
+FETCH BACKWARD FROM c;
+FETCH NEXT FROM c;
+
+-- scroll beyond end end
+FETCH LAST FROM c;
+FETCH BACKWARD FROM c;
+FETCH NEXT FROM c;
+FETCH NEXT FROM c;
+FETCH NEXT FROM c;
+FETCH BACKWARD FROM c;
+FETCH NEXT FROM c;
+
+COMMIT;
+
+-- disk based
+BEGIN;
+SET LOCAL enable_indexscan = false;
+SET LOCAL work_mem = '100kB';
+-- unfortunately can't show analyze output confirming sort method,
+-- the memory used output wouldn't be stable
+EXPLAIN (COSTS OFF) DECLARE c SCROLL CURSOR FOR SELECT noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing;
+DECLARE c SCROLL CURSOR FOR SELECT noabort_decreasing FROM abbrev_abort_uuids ORDER BY noabort_decreasing;
+
+-- first and second
+FETCH NEXT FROM c;
+FETCH NEXT FROM c;
+
+-- scroll beyond beginning
+FETCH BACKWARD FROM c;
+FETCH BACKWARD FROM c;
+FETCH BACKWARD FROM c;
+FETCH BACKWARD FROM c;
+FETCH NEXT FROM c;
+
+-- scroll beyond end end
+FETCH LAST FROM c;
+FETCH BACKWARD FROM c;
+FETCH NEXT FROM c;
+FETCH NEXT FROM c;
+FETCH NEXT FROM c;
+FETCH BACKWARD FROM c;
+FETCH NEXT FROM c;
+
+COMMIT;
+
+
+----
+-- test tuplesort using both in-memory and disk sort
+---
+
+-- memory based
+SELECT
+    -- fixed-width by-value datum
+    (array_agg(id ORDER BY id DESC NULLS FIRST))[0:5],
+    -- fixed-width by-ref datum
+    (array_agg(abort_increasing ORDER BY abort_increasing DESC NULLS LAST))[0:5],
+    -- variable-width datum
+    (array_agg(id::text ORDER BY id::text DESC NULLS LAST))[0:5],
+    -- fixed width by-value datum tuplesort
+    percentile_disc(0.99) WITHIN GROUP (ORDER BY id),
+    -- ensure state is shared
+    percentile_disc(0.01) WITHIN GROUP (ORDER BY id),
+    -- fixed width by-ref datum tuplesort
+    percentile_disc(0.8) WITHIN GROUP (ORDER BY abort_increasing),
+    -- variable width by-ref datum tuplesort
+    percentile_disc(0.2) WITHIN GROUP (ORDER BY id::text),
+    -- multi-column tuplesort
+    rank('00000000-0000-0000-0000-000000000000', '2', '2') WITHIN GROUP (ORDER BY noabort_increasing, id, id::text)
+FROM (
+    SELECT * FROM abbrev_abort_uuids
+    UNION ALL
+    SELECT NULL, NULL, NULL, NULL, NULL) s;
+
+-- disk based (see also above)
+BEGIN;
+SET LOCAL work_mem = '100kB';
+
+SELECT
+    (array_agg(id ORDER BY id DESC NULLS FIRST))[0:5],
+    (array_agg(abort_increasing ORDER BY abort_increasing DESC NULLS LAST))[0:5],
+    (array_agg(id::text ORDER BY id::text DESC NULLS LAST))[0:5],
+    percentile_disc(0.99) WITHIN GROUP (ORDER BY id),
+    percentile_disc(0.01) WITHIN GROUP (ORDER BY id),
+    percentile_disc(0.8) WITHIN GROUP (ORDER BY abort_increasing),
+    percentile_disc(0.2) WITHIN GROUP (ORDER BY id::text),
+    rank('00000000-0000-0000-0000-000000000000', '2', '2') WITHIN GROUP (ORDER BY noabort_increasing, id, id::text)
+FROM (
+    SELECT * FROM abbrev_abort_uuids
+    UNION ALL
+    SELECT NULL, NULL, NULL, NULL, NULL) s;
+
+ROLLBACK;
+
+
+----
+-- test tuplesort mark/restore
+---
+
+CREATE TABLE test_mark_restore(col1 int, col2 int, col12 int);
+-- need a few duplicates for mark/restore to matter
+INSERT INTO test_mark_restore(col1, col2, col12)
+   SELECT a.i, b.i, a.i * b.i FROM generate_series(1, 500) a(i), generate_series(1, 5) b(i);
+
+BEGIN;
+
+SET LOCAL enable_nestloop = off;
+SET LOCAL enable_hashjoin = off;
+
+-- set query into variable once, to avoid repetition of the fairly long query
+SELECT $$
+    SELECT col12, count(distinct a.col1), count(distinct a.col2), count(distinct b.col1), count(distinct b.col2), count(*)
+    FROM test_mark_restore a
+        JOIN test_mark_restore b USING(col12)
+    GROUP BY 1
+    HAVING count(*) > 1
+    ORDER BY 2 DESC, 1 DESC, 3 DESC, 4 DESC, 5 DESC, 6 DESC
+    LIMIT 10
+$$ AS qry \gset
+
+-- test mark/restore with in-memory sorts
+EXPLAIN (COSTS OFF) :qry;
+:qry;
+
+-- test mark/restore with on-disk sorts
+SET LOCAL work_mem = '100kB';
+EXPLAIN (COSTS OFF) :qry;
+:qry;
+
+COMMIT;
+
+
+-- cleanup
+DROP TABLE IF EXISTS abbrev_abort_uuids;
+DROP TABLE IF EXISTS test_mark_restore;