Re: Core team statement on replication in PostgreSQL

From: "Gurjeet Singh" <singh(dot)gurjeet(at)gmail(dot)com>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Core team statement on replication in PostgreSQL
Date: 2008-05-30 20:21:28
Message-ID: 65937bea0805301321x668b8b1fxe15d86243ee8fcaf@mail.gmail.com
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On Thu, May 29, 2008 at 7:42 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> The big problem
> is that long-running slave-side queries might still need tuples that are
> vacuumable on the master, and so replication of vacuuming actions would
> cause the slave's queries to deliver wrong answers.

Another issue with read-only slaves just popped up in my head.

How do we block the readers on the slave while it is replaying an ALTER
TABLE or similar command that requires Exclusive lock and potentially alters
the table's structure. Or does the WAL replay already takes an x-lock on
such a table?

Best regards,
--
gurjeet[(dot)singh](at)EnterpriseDB(dot)com
singh(dot)gurjeet(at){ gmail | hotmail | indiatimes | yahoo }.com

EnterpriseDB http://www.enterprisedb.com

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