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Re: Hot Backup with rsync fails at pg_clog if under load

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Florian Pflug <fgp(at)phlo(dot)org>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, Daniel Farina <daniel(at)heroku(dot)com>, Chris Redekop <chris(at)replicon(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Hot Backup with rsync fails at pg_clog if under load
Date: 2011-10-27 09:37:48
Message-ID: CA+U5nMKx-N5Qmn6FwpvSoLhTqDp70U+tWJ59=t=--KUH3uhP7g@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, Oct 27, 2011 at 4:36 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Wed, Oct 26, 2011 at 12:16 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>>> This fixes both the subtrans and clog bugs in one patch.
>
>> I don't see the point of changing StartupCLOG() to be an empty
>> function and adding a new function TrimCLOG() that does everything
>> StartupCLOG() used to do.
>
> +1 ... I found that overly cute also.

It would have been even easier to move StartupCLOG() later, but then
we'd need a big comment explaining why CLOG starts up at one point and
subtrans starts up at another point, since that is very confusing way
of doing things. I wrote it that way first and it definitely looks
strange.

It's much easier to understand that StartupCLOG() is actually a no-op
and that we need to trim the clog at the end of recovery in all cases.

The patch isn't meant to be cute, just a better of way of expressing
what needs to be done, so I think the patch should stay that way.

-- 
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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