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Date: Tue, 27 Aug 2013 12:31:35 -0700 (PDT)
From: Kevin Grittner <kgrittn@ymail.com>
Reply-To: Kevin Grittner <kgrittn@ymail.com>
Subject: Re: several questions about pg_dumpall, pg_start_backup,
 pg_basebackup and WAL
To: Patrick Dung <patrick_dkt@yahoo.com.hk>,
 Albe Laurenz <laurenz.albe@wien.gv.at>,
 "pgsql-admin@postgresql.org" <pgsql-admin@postgresql.org>
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Patrick Dung <patrick_dkt@yahoo.com.hk> wrote:
> Albe Laurenz <laurenz.albe@wien.gv.at>
>> Patrick Dung wrote:

>>> It is possible that there is file changes (added or file size
>>> changed) between the pg_start_backup and pg_stop_backup.
>>
>> Yes.
>>
>>> Is the backup consistent?
>>
>> The tar or snapshot itself will not be consistent, it will have
>> to be recovered at least until the end on the online backup.
>
> I should ask: is the backup crash consistent?

PITR restore procedures will use the crash recovery mechanism to
make the database consistent, if that's what you mean.

> Which means it is consistent at the time that the pg_start_backup
> is run.

No.=A0 It will be consistent with the time that pg_stop_backup was
run, or any later point in time that you choose, as long as you
have WAL to that point in time.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company


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