Re: WAL archive on slave

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От James Sewell
Тема Re: WAL archive on slave
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Msg-id CANkGpBsMrvfcgcnYP_vSnyugzq+2xskHoiAsL+q_7OMoFS6H=A@mail.gmail.com
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Ответ на Re: WAL archive on slave  (Albe Laurenz <laurenz.albe@wien.gv.at>)
Ответы Re: WAL archive on slave  (James Sewell <james.sewell@lisasoft.com>)
Список pgsql-general
Thanks for the reply Albe.

I have WAL archiving enabled on both my servers, but it only happens on the master. 

When I promote the slave to be the new master then it will start archiving automatically, which suggests that my configuration is correct.

Can you think of anything else which might cause this?

Cheers,


James Sewell,
PostgreSQL Team Lead / Solutions Architect
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Level 2, 50 Queen St, Melbourne VIC 3000

(+61) 3 8370 8000  W www.lisasoft.com  (+61) 3 8370 8099
 


On Fri, Feb 7, 2014 at 7:30 PM, Albe Laurenz <laurenz.albe@wien.gv.at> wrote:
James Sewell wrote:
> My understanding is that WAL archiving can not be enabled on the slave in a streaming replication
> pair.

It can be enabled.  Did you try it?

> If this is correct, is there a reason behind it? I can see logs showing up in pg_xlog, so could they
> not be archived?

These are files containing the WAL data replicated from the master.
They won't be archived.

> The reason I ask is if this happened it would allow the following with a streaming replication pair
> (A,B):
>
>
> 1.    Start A as master
> 2.    Attach B as slave using basebackup
> 3.    work ....
> 4.    Promote B to master
>
> 5.    Restore A from a scheduled backup to a time before promotion
> 6.    Attach A as slave pointing at B's WAL archive
>
> If we used A's WAL archive in this case and A had writes after the promotion then we would get
> timeline errors.

You shouldn't with 9.3, because in that case A would follow the
timeline switch introduced by B's promotion rather than its old timelime.
http://www.postgresql.org/message-id/E1TjCRc-00084r-1H@gemulon.postgresql.org

I may be missing something there since I have never tried it.

> As far as I can tell, using the WAL archive from B would resolve this issue.

That should work in any event.

Yours,
Laurenz Albe



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