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Re: Keepalive for max_standby_delay

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Keepalive for max_standby_delay
Date: 2010-07-03 20:18:11
Message-ID: 14694.1278188291@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> On 03/07/10 18:32, Tom Lane wrote:
>> That would not do what you want at all in the case where you're
>> recovering from archive --- XLogReceiptTime would never advance
>> at all for the duration of the recovery.

> Do you mean when using something like pg_standby, which does the waiting 
> itself?

No, I'm thinking about recovery starting from an old base backup, or any
situation where you're trying to process a significant number of
archived WAL segments as quickly as possible.

>> It might be useful if you knew that it was a standby-with-log-shipping
>> situation, but we have no way to tell the difference.

> With pg_standby etc. you use standby_mode=off. Same with traditional 
> archive recovery. In standby mode, it's on.

Uh, no, that parameter is not what I'm talking about.  What I tried to
say is that if you're using log shipping for replication instead of
walsender/walreceiver, you might want to treat data as live even though
the database thinks it is being pulled "from archive".  But we'd need
a way for the database to tell the cases apart ... right now it cannot.

			regards, tom lane

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