Test for IOS/Vacuum race conditions in index AMs

Add regression tests that demonstrate wrong results can occur with index-only
scans in GiST and SP-GiST indexes when encountering tuples being removed by a
concurrent VACUUM operation.

With these tests the index AMs are also expected to not block VACUUM even when
they're used inside a cursor.

Co-authored-by: Matthias van de Meent <boekewurm+postgres@gmail.com>
Co-authored-by: Peter Geoghegan <pg@bowt.ie>
Co-authored-by: Michail Nikolaev <michail.nikolaev@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/CANtu0oi0rkR%2BFsgyLXnGZ-uW2950-urApAWLhy-%2BV1WJD%3D_ZXA%40mail.gmail.com

Author: 3 people

src/test/isolation/expected/index-only-scan-btree-vacuum.out

@@ -0,0 +1,59 @@
+Parsed test spec with 2 sessions
+
+starting permutation: s2_mod s1_begin s1_prepare_sorted_asc s1_fetch_1 s2_vacuum s1_fetch_all s1_commit
+step s2_mod: 
+  DELETE FROM ios_needs_cleanup_lock WHERE a BETWEEN 2 AND 9;
+
+step s1_begin: BEGIN;
+step s1_prepare_sorted_asc: 
+	DECLARE foo NO SCROLL CURSOR FOR SELECT a as x FROM ios_needs_cleanup_lock ORDER BY a ASC;
+
+step s1_fetch_1: 
+	FETCH FROM foo;
+
+x
+-
+1
+(1 row)
+
+step s2_vacuum: 
+  VACUUM (TRUNCATE false) ios_needs_cleanup_lock;
+
+step s1_fetch_all: 
+	FETCH ALL FROM foo;
+
+ x
+--
+10
+(1 row)
+
+step s1_commit: COMMIT;
+
+starting permutation: s2_mod s1_begin s1_prepare_sorted_desc s1_fetch_1 s2_vacuum s1_fetch_all s1_commit
+step s2_mod: 
+  DELETE FROM ios_needs_cleanup_lock WHERE a BETWEEN 2 AND 9;
+
+step s1_begin: BEGIN;
+step s1_prepare_sorted_desc: 
+	DECLARE foo NO SCROLL CURSOR FOR SELECT a as x FROM ios_needs_cleanup_lock ORDER BY a DESC;
+
+step s1_fetch_1: 
+	FETCH FROM foo;
+
+ x
+--
+10
+(1 row)
+
+step s2_vacuum: 
+  VACUUM (TRUNCATE false) ios_needs_cleanup_lock;
+
+step s1_fetch_all: 
+	FETCH ALL FROM foo;
+
+x
+-
+1
+(1 row)
+
+step s1_commit: COMMIT;

src/test/isolation/expected/index-only-scan-gist-vacuum.out

@@ -0,0 +1,53 @@
+Parsed test spec with 2 sessions
+
+starting permutation: s2_mod s1_begin s1_prepare_sorted s1_fetch_1 s2_vacuum s1_fetch_all s1_commit
+step s2_mod: 
+  DELETE FROM ios_needs_cleanup_lock WHERE a != point '(1,1)';
+
+step s1_begin: BEGIN;
+step s1_prepare_sorted: 
+	DECLARE foo NO SCROLL CURSOR FOR SELECT a <-> point '(0,0)' as x FROM ios_needs_cleanup_lock ORDER BY a <-> point '(0,0)';
+
+step s1_fetch_1: 
+	FETCH FROM foo;
+
+                 x
+------------------
+1.4142135623730951
+(1 row)
+
+step s2_vacuum: VACUUM (TRUNCATE false) ios_needs_cleanup_lock;
+step s1_fetch_all: 
+	FETCH ALL FROM foo;
+
+x
+-
+(0 rows)
+
+step s1_commit: COMMIT;
+
+starting permutation: s2_mod s1_begin s1_prepare_unsorted s1_fetch_1 s2_vacuum s1_fetch_all s1_commit
+step s2_mod: 
+  DELETE FROM ios_needs_cleanup_lock WHERE a != point '(1,1)';
+
+step s1_begin: BEGIN;
+step s1_prepare_unsorted: 
+	DECLARE foo NO SCROLL CURSOR FOR SELECT a FROM ios_needs_cleanup_lock WHERE box '((-100,-100),(100,100))' @> a;
+
+step s1_fetch_1: 
+	FETCH FROM foo;
+
+a    
+-----
+(1,1)
+(1 row)
+
+step s2_vacuum: VACUUM (TRUNCATE false) ios_needs_cleanup_lock;
+step s1_fetch_all: 
+	FETCH ALL FROM foo;
+
+a
+-
+(0 rows)
+
+step s1_commit: COMMIT;

src/test/isolation/expected/index-only-scan-spgist-vacuum.out

@@ -0,0 +1,53 @@
+Parsed test spec with 2 sessions
+
+starting permutation: s2_mod s1_begin s1_prepare_sorted s1_fetch_1 s2_vacuum s1_fetch_all s1_commit
+step s2_mod: 
+  DELETE FROM ios_needs_cleanup_lock WHERE a != point '(1,1)';
+
+step s1_begin: BEGIN;
+step s1_prepare_sorted: 
+	DECLARE foo NO SCROLL CURSOR FOR SELECT a <-> point '(0,0)' as x FROM ios_needs_cleanup_lock ORDER BY a <-> point '(0,0)';
+
+step s1_fetch_1: 
+	FETCH FROM foo;
+
+                 x
+------------------
+1.4142135623730951
+(1 row)
+
+step s2_vacuum: VACUUM (TRUNCATE false) ios_needs_cleanup_lock;
+step s1_fetch_all: 
+	FETCH ALL FROM foo;
+
+x
+-
+(0 rows)
+
+step s1_commit: COMMIT;
+
+starting permutation: s2_mod s1_begin s1_prepare_unsorted s1_fetch_1 s2_vacuum s1_fetch_all s1_commit
+step s2_mod: 
+  DELETE FROM ios_needs_cleanup_lock WHERE a != point '(1,1)';
+
+step s1_begin: BEGIN;
+step s1_prepare_unsorted: 
+	DECLARE foo NO SCROLL CURSOR FOR SELECT a FROM ios_needs_cleanup_lock WHERE box '((-100,-100),(100,100))' @> a;
+
+step s1_fetch_1: 
+	FETCH FROM foo;
+
+a    
+-----
+(1,1)
+(1 row)
+
+step s2_vacuum: VACUUM (TRUNCATE false) ios_needs_cleanup_lock;
+step s1_fetch_all: 
+	FETCH ALL FROM foo;
+
+a
+-
+(0 rows)
+
+step s1_commit: COMMIT;

src/test/isolation/isolation_schedule

@@ -18,6 +18,9 @@ test: two-ids
 test: multiple-row-versions
 test: index-only-scan
 test: index-only-bitmapscan
+test: index-only-scan-btree-vacuum
+test: index-only-scan-gist-vacuum
+test: index-only-scan-spgist-vacuum
 test: predicate-lock-hot-tuple
 test: update-conflict-out
 test: deadlock-simple

src/test/isolation/specs/index-only-scan-btree-vacuum.spec

@@ -0,0 +1,113 @@
+# index-only-scan test showing correct results with btree even with concurrent
+# vacuum
+
+setup
+{
+	-- by using a low fillfactor and a wide tuple we can get multiple blocks
+	-- with just few rows
+	CREATE TABLE ios_needs_cleanup_lock (a int NOT NULL, pad char(1024) default '')
+	WITH (AUTOVACUUM_ENABLED = false, FILLFACTOR = 10);
+
+	INSERT INTO ios_needs_cleanup_lock SELECT g.i FROM generate_series(1, 10) g(i);
+
+	CREATE INDEX ios_btree_a ON ios_needs_cleanup_lock USING btree (a);
+}
+setup
+{
+	VACUUM (ANALYZE) ios_needs_cleanup_lock;
+}
+
+teardown
+{
+	DROP TABLE ios_needs_cleanup_lock;
+}
+
+
+session s1
+
+# Force an index-only scan, where possible:
+setup {
+	SET enable_bitmapscan = false;
+	SET enable_indexonlyscan = true;
+	SET enable_indexscan = true;
+}
+
+step s1_begin { BEGIN; }
+step s1_commit { COMMIT; }
+
+step s1_prepare_sorted_asc {
+	DECLARE foo NO SCROLL CURSOR FOR SELECT a as x FROM ios_needs_cleanup_lock ORDER BY a ASC;
+}
+step s1_prepare_sorted_desc {
+	DECLARE foo NO SCROLL CURSOR FOR SELECT a as x FROM ios_needs_cleanup_lock ORDER BY a DESC;
+}
+
+step s1_fetch_1 {
+	FETCH FROM foo;
+}
+
+step s1_fetch_all {
+	FETCH ALL FROM foo;
+}
+
+
+session s2
+
+# Don't delete row 1, nor 10, so we have a row for the cursor to "rest" on.
+step s2_mod
+{
+  DELETE FROM ios_needs_cleanup_lock WHERE a BETWEEN 2 AND 9;
+}
+
+# Disable truncation, as otherwise we'll just wait for a timeout while trying
+# to acquire the lock
+step s2_vacuum
+{
+  VACUUM (TRUNCATE false) ios_needs_cleanup_lock;
+}
+
+permutation
+  # delete nearly all rows, to make issue visible
+  s2_mod
+  # create a cursor
+  s1_begin
+  s1_prepare_sorted_asc
+
+  # fetch one row from the cursor, that ensures the index scan portion is done
+  # before the vacuum in the next step
+  s1_fetch_1
+
+  # with the bug this vacuum will mark pages as all-visible that the scan in
+  # the next step then considers all-visible, despite all rows from those
+  # pages having been removed.
+  # Because this should block on buffer-level locks, this won't ever be
+  # considered "blocked" by isolation tester, and so we only have a single
+  # step we can work with concurrently.
+  s2_vacuum
+
+  # if this returns any rows, we're busted
+  s1_fetch_all
+
+  s1_commit
+
+permutation
+  # delete nearly all rows, to make issue visible
+  s2_mod
+  # create a cursor
+  s1_begin
+  s1_prepare_sorted_desc
+
+  # fetch one row from the cursor, that ensures the index scan portion is done
+  # before the vacuum in the next step
+  s1_fetch_1
+
+  # If the index scan doesn't correctly interlock its visibility tests with
+  # concurrent VACUUM cleanup then VACUUM will mark pages as all-visible that
+  # the scan in the next steps may then consider all-visible, despite some of
+  # those rows having been removed.
+  s2_vacuum
+
+  # if this returns any rows, we're busted
+  s1_fetch_all
+
+  s1_commit