Date: Tue, 5 Feb 2019 18:11:19 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Arseny Sher <a.sher@postgrespro.ru>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>,
	Alexander Lakhin <a.lakhin@postgrespro.ru>
Subject: Re: Too rigorous assert in reorderbuffer.c
Message-ID: <20190205211118.GA30474@alvherre.pgsql>
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On 2019-Jan-31, Arseny Sher wrote:

> My colleague Alexander Lakhin has noticed an assertion failure in
> reorderbuffer.c:1330. Here is a simple snippet reproducing it:
> 
> SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
> 
> create table t(k int);
> begin;
> savepoint a;
> alter table t alter column k type text;
> rollback to savepoint a;
> alter table t alter column k type bigint;
> commit;
> 
> SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');

Hmm, the new test introduced by your patch fails in early branches (at
least 9.4): the transaction is decoded like this:

!                         data                         
! -----------------------------------------------------
   BEGIN
   table public.tr_sub_ddl: INSERT: data[integer]:42
+  table public.pg_temp_16445: INSERT: data[bigint]:42
   table public.tr_sub_ddl: INSERT: data[bigint]:43
   COMMIT
! (5 rows)

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.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services