| From: | Scott Ribe <scott_ribe(at)elevated-dev(dot)com> |
|---|---|
| To: | "Williams, Alex" <awilliams(at)teamdrg(dot)com> |
| Cc: | "pgsql-admin(at)postgresql(dot)org" <pgsql-admin(at)postgresql(dot)org> |
| Subject: | Re: Question on Hot Standby in PostgreSQL |
| Date: | 2015-11-23 20:24:07 |
| Message-ID: | 88C8194B-0F69-4CEA-9DB4-5A21D156D2DE@elevated-dev.com |
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| Thread: | |
| Lists: | pgsql-admin |
On Nov 20, 2015, at 12:50 PM, Williams, Alex <awilliams(at)teamdrg(dot)com> wrote:
>
> However, I thought with the use of MVCC,
> an active query on the slave (long running, 30 seconds+) can run reading
> from row xid versions/snapshot...
The problem is that the master could well make changes that would remove rows in that snapshot because the master does not know anything about the rows that need preserving for the replica's query.
That said, IIRC there may be something in 9.4 or 9.5 which provides for the replica to send that info to the server in order to coordinate things, but I haven't used that and so cannot offer more.
--
Scott Ribe
scott_ribe(at)elevated-dev(dot)com
http://www.elevated-dev.com/
https://www.linkedin.com/in/scottribe/
(303) 722-0567 voice
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