| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Simon Riggs <simon(at)2ndQuadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org, Merlin Moncure <mmoncure(at)gmail(dot)com>, Gregory Stark <stark(at)enterprisedb(dot)com>, Csaba Nagy <nagy(at)ecircle-ag(dot)com>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Chris Browne <cbbrowne(at)acm(dot)org>, Jochem van Dieten <jochemd(at)gmail(dot)com>, Dimitri Fontaine <dfontaine(at)hi-media(dot)com>, Hannu Krosing <hannu(at)2ndQuadrant(dot)com>, Richard Huxton <dev(at)archonet(dot)com> |
| Subject: | Re: Transaction Snapshots and Hot Standby |
| Date: | 2008-09-25 01:22:49 |
| Message-ID: | 200809250122.m8P1Mnj03942@momjian.us |
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| Lists: | pgsql-hackers |
Bruce Momjian wrote:
> Simon Riggs wrote:
> > 2. Master ignores Standby's OldestXmin
> > Effects:
> > * Long running queries on standby...
> > Have no effect on primary
> > Can delay apply of WAL records on standby
> > * Queries on standby give consistent answers in all cases.
>
> Just for clarification, if you set a max_slave_delay it means it is the
> maximum amount of time WAL replay can be delayed on the slave, _and_ it
> is the maximum amount of time a query/snapshot can be guaranteed to run
> without the possibility of being canceled. My point is that these two
> concepts are linked to the same setting.
FYI, max_slave_delay does not relate to the amount of time of data loss
in the case of master failure, assuming the WAL files are stored on the
slave in some way during the delay.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
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