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Re: Disabled features on Hot Standby

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Noah Misch <noah(at)leadboat(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Disabled features on Hot Standby
Date: 2012-01-14 11:36:52
Message-ID: CA+U5nM+AajL=MYEYq6LZJT9-wnfxZA71CeCKiS_PP1PU2ZgwXA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Sat, Jan 14, 2012 at 11:17 AM, Noah Misch <noah(at)leadboat(dot)com> wrote:
> On Sat, Jan 14, 2012 at 08:08:29AM +0000, Simon Riggs wrote:
>> On Sat, Jan 14, 2012 at 1:02 AM, Noah Misch <noah(at)leadboat(dot)com> wrote:
>> > However, CLUSTER/VACUUM FULL already
>> > remove tuples still-visible to standby snapshots without provoking a recovery
>> > conflict. ?(Again only with hot_standby_feedback=off.)
>>
>> If that were the case it would be a bug.
>>
>> CLUSTER/VACUUM FULL emit an AccessExclusiveLock record that would
>> conflict with any current lock holders, so should be fine on that.
>
> I speak of this sequence (M = master connection, S = standby connection):
>
> M: CREATE TABLE t AS SELECT * FROM generate_series(1,1000) t(n);
> S: BEGIN ISOLATION LEVEL REPEATABLE READ; SELECT 0;
> M: DELETE FROM t WHERE n <= 10;
> M: VACUUM FULL t;
> S: SELECT count(*) FROM t; -- 990, should be 1000

OK, so we need to emit a heap_xlog_cleanup_info() record at the end of
cluster to conflict with anybody that doesn't yet have a lock but has
a snapshot that can see tuples the cluster implicitly removed. Will
do.

-- 
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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