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Re: Cost of XLogInsert CRC calculations

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Greg Stark <gsstark(at)mit(dot)edu>,Mark Cave-Ayland <m(dot)cave-ayland(at)webbased(dot)co(dot)uk>,"'Manfred Koizar'" <mkoi-pg(at)aon(dot)at>,"'Bruce Momjian'" <pgman(at)candle(dot)pha(dot)pa(dot)us>,pgsql-hackers(at)postgresql(dot)org
Subject: Re: Cost of XLogInsert CRC calculations
Date: 2005-06-01 02:36:29
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> Hmmm. I seem to recall asking myself why xl_prev existed if it wasn't
> used, but passed that by. Damn.

I couldn't believe it'd been overlooked this long, either.  It's the
sort of thing that you assume got done the first time :-(

> PreAllocXLog was already a reason to have somebody prepare new xlog
> files ahead of them being used. Surely the right solution here is to
> have that agent prepare fresh/zeroed files prior to them being required.

Uh, why?  That doubles the amount of physical I/O required to maintain
the WAL, and AFAICS it doesn't really add any safety that we can't get
in a more intelligent fashion.

			regards, tom lane

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