Re: Too rigorous assert in reorderbuffer.c

Alvaro Herrera <alvherre@2ndquadrant.com> writes:

> note the additional pg_temp_XYZ row in the middle.  This is caused by
> the rewrite in ALTER TABLE.  Peter E fixed that in Pg11 in commit
> 325f2ec55; I don't think there's much to do in the backbranches other
> than hide the pesky record to avoid it breaking the test.

Oh, I see. Let's just remove the first insertion then, as in attached.
I've tested it on master and on 9.4.

--
Arseny Sher
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company


From b34726d9b7565df73319a44664d9cd04de5f514f Mon Sep 17 00:00:00 2001
From: Arseny Sher <sher-ars@yandex.ru>
Date: Wed, 30 Jan 2019 23:31:47 +0300
Subject: [PATCH] Remove assertion in reorderbuffer that cmax is stable.

Since it can be rewritten arbitrary number of times if subxact(s) who tried to
delete some tuple version abort later. Add small test involving DDL in aborted
subxact as this case is interesting on its own and wasn't covered before.
---
 contrib/test_decoding/expected/ddl.out          | 18 ++++++++++++++++++
 contrib/test_decoding/sql/ddl.sql               | 13 +++++++++++++
 src/backend/replication/logical/reorderbuffer.c | 10 ++++++----
 3 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/contrib/test_decoding/expected/ddl.out b/contrib/test_decoding/expected/ddl.out
index b7c76469fc..2bd28e6d15 100644
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -409,6 +409,24 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
  COMMIT
 (6 rows)
 
+-- check that DDL in aborted subtransactions handled correctly
+CREATE TABLE tr_sub_ddl(data int);
+BEGIN;
+SAVEPOINT a;
+ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE text;
+INSERT INTO tr_sub_ddl VALUES ('blah-blah');
+ROLLBACK TO SAVEPOINT a;
+ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE bigint;
+INSERT INTO tr_sub_ddl VALUES(43);
+COMMIT;
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts',
'1');
+                       data                       
+--------------------------------------------------
+ BEGIN
+ table public.tr_sub_ddl: INSERT: data[bigint]:43
+ COMMIT
+(3 rows)
+
 /*
  * Check whether treating a table as a catalog table works somewhat
  */
diff --git a/contrib/test_decoding/sql/ddl.sql b/contrib/test_decoding/sql/ddl.sql
index c4b10a4cf9..a55086443c 100644
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -236,6 +236,19 @@ COMMIT;
 
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts',
'1');
 
+-- check that DDL in aborted subtransactions handled correctly
+CREATE TABLE tr_sub_ddl(data int);
+BEGIN;
+SAVEPOINT a;
+ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE text;
+INSERT INTO tr_sub_ddl VALUES ('blah-blah');
+ROLLBACK TO SAVEPOINT a;
+ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE bigint;
+INSERT INTO tr_sub_ddl VALUES(43);
+COMMIT;
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts',
'1');
+
 
 /*
  * Check whether treating a table as a catalog table works somewhat
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index a49e226967..0ace0cfb87 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -1327,13 +1327,15 @@ ReorderBufferBuildTupleCidHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
         else
         {
             Assert(ent->cmin == change->data.tuplecid.cmin);
-            Assert(ent->cmax == InvalidCommandId ||
-                   ent->cmax == change->data.tuplecid.cmax);
 
             /*
              * if the tuple got valid in this transaction and now got deleted
-             * we already have a valid cmin stored. The cmax will be
-             * InvalidCommandId though.
+             * we already have a valid cmin stored. The cmax is still
+             * InvalidCommandId though, so stamp it. Moreover, cmax might
+             * be rewritten arbitrary number of times if subxacts who tried to
+             * delete this version abort later. Pick up the latest since it is
+             * (belonging to potentially committed subxact) the only one which
+             * matters.
              */
             ent->cmax = change->data.tuplecid.cmax;
         }
-- 
2.11.0