Re: "Hot standby"?

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com>
Cc: David Fetter <david(at)fetter(dot)org>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Bruce Momjian <bruce(at)momjian(dot)us>, Peter Eisentraut <peter_e(at)gmx(dot)net>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: "Hot standby"?
Date: 2009-08-11 19:00:15
Message-ID: 603c8f070908111200tbc89acmcf80875173b3a362@mail.gmail.com
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On Tue, Aug 11, 2009 at 2:10 PM, Ron Mayer<rm_pg(at)cheapcomplexdevices(dot)com> wrote:
> David Fetter wrote:
>> On Tue, Aug 11, 2009 at 08:56:38AM -0500, Kevin Grittner wrote:
>>> Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>>>
>>>> OK, so it is "warm slave".
>
> Why isn't it just a "read only slave".  Do some systems
> have read-only slave databases that can't serve as a warm
> standby system as well as this one could?

I think that's about right. What we have now via pg_standby or
similar tools is a warm standby. What this tool does is makes the
warm-standby also serve as a read-only slave. It doesn't make
failover any simpler so it's not making the standby any hotter - it
instead makes the standby be able to do more useful work when no
failover has occurred.

The technical description for the commit message is probably something
like this:

"Allow read-only queries to be processed during archive recovery."

The P/R version is probably something like this:

"Warm standby servers now function as read-only slaves."

...Robert

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