From: | Kevin Grittner <kgrittn(at)gmail(dot)com> |
---|---|
To: | Greg Stark <stark(at)mit(dot)edu> |
Cc: | Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Rajeev rastogi <rajeev(dot)rastogi(at)huawei(dot)com>, Markus Wanner <markus(at)bluegap(dot)ch>, Ants Aasma <ants(at)cybertec(dot)at>, Bruce Momjian <bruce(at)momjian(dot)us>, obartunov <obartunov(at)postgrespro(dot)ru>, Teodor Sigaev <teodor(at)postgrespro(dot)ru> |
Subject: | Re: Proposal for CSN based snapshots |
Date: | 2016-08-10 18:36:54 |
Message-ID: | CACjxUsPi8Bs-=swbKrLUKVBjVD3xEc_cvkqT+Gfz_qYvoRvECQ@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On Wed, Aug 10, 2016 at 12:26 PM, Greg Stark <stark(at)mit(dot)edu> wrote:
> Complexity like this makes it hard to implement other features such as
> CSNs. IIRC this already bit hot standby as well. I think it would be a
> big improvement if we had a clear, well defined commit order that was
> easy to explain and easy to reason about when new changes are being
> made.
And here I was getting concerned that there was no mention of
"apparent order of execution" for serializable transactions --
which does not necessarily match either the order of LSNs from
commit records nor CSNs. The order in which transactions become
visible is clearly a large factor in determining AOoE, but it is
secondary to looking at whether a transaction modified data based
on reading the "before" image of a data set modified by a
concurrent transaction.
I still think that our best bet for avoiding anomalies when using
logical replication in complex environments is for logical
replication to apply transactions in apparent order of execution.
--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
From | Date | Subject | |
---|---|---|---|
Next Message | Alexander Korotkov | 2016-08-10 18:39:41 | Re: Proposal for CSN based snapshots |
Previous Message | Tomas Vondra | 2016-08-10 18:34:58 | Re: multivariate statistics (v19) |