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Re: Query Plans on Slaves - Mailing list pgsql-general

From Anthony Presley
Subject Re: Query Plans on Slaves
Date
Msg-id CALL+CaqB9PCrT6+MN0TCvUaPUV4f+T7PkLU==V3-MStRtZVgxQ@mail.gmail.com
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In response to Re: Query Plans on Slaves  (Tatsuo Ishii <ishii@postgresql.org>)
Responses Re: Query Plans on Slaves  (Tatsuo Ishii <ishii@postgresql.org>)
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We're still considering this architecture - so I don't have any plans.

My question is, does the ANALYZE command, which is only executed on the master, mean that the statistics / plans that are used on the master are ALSO used on the slaves?  OR .... does the slave create it's own plan?

I would anticipate very different plans between the two machines, and different postgresql.conf settings as well.

I would *want* different query plans between the two.  Is that possible?


On Sun, Nov 9, 2014 at 8:50 PM, Tatsuo Ishii <ishii@postgresql.org> wrote:
> Hi all!
>
> We're working on our architecture for our next set of systems, and we
> normally have a simple master/slave with wal shipping and hot_standby set
> up, with pgpool sitting in front of both to do load balancing.
>
> However, one piece I'm very confused about is the query plans on the slave
> server.
>
> Let's pretend we have a master server with:
>   (2) E5-2660 CPU's
>   (4) S3700 400GB SSD's
>   256GB of RAM
>
> And multiple slave servers that looks like:
>   (1) E3-1290 CPU's
>   (2) Intel 520 SSD's
>   32GB of RAM
>
> There's a significant difference between the master and slaves.

Can you show us the explain analyze result on both master and slave?

> Does the ANALYZE command run on each system, and work differently on each
> system, or would the slave servers use the query plans from the master
> machine?

ANALYZE can only be executed on master. Slave creates its own
plan. However since statistics should be same as master, I guess if
you get different plan, then postgresql.conf maybe different among
master and slave.

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp

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