From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
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To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Keepalive for max_standby_delay |
Date: | 2010-05-15 16:30:38 |
Message-ID: | 4BEECC2E.5080707@enterprisedb.com |
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Lists: | pgsql-hackers |
Simon Riggs wrote:
> On Sat, 2010-05-15 at 11:45 -0400, Tom Lane wrote:
>> I'm also extremely dubious that it's a good idea to set
>> recoveryLastXTime from this. Using both that and the timestamps from
>> the wal log flies in the face of everything I remember about control
>> theory. We should be doing only one or only the other, I think.
>
> I can change it so that the recoveryLastXTime will not be updated if we
> are using the value from the keepalives. So we have one, or the other.
> Remember that replication can switch backwards and forwards between
> modes, so it seems sensible to have a common timing value whichever mode
> we're in.
That means that recoveryLastXTime can jump forwards and backwards.
Doesn't feel right to me either. If you want to expose the
keepalive-time to queries, it should be a separate field, something like
lastMasterKeepaliveTime and a pg_last_master_keepalive() function to
read it.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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