From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Christopher Browne <cbbrowne(at)acm(dot)org>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Automatic free space map filling |
Date: | 2006-03-02 16:09:04 |
Message-ID: | 200603021609.k22G94V03960@candle.pha.pa.us |
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Lists: | pgsql-hackers |
Tom Lane wrote:
> Christopher Browne <cbbrowne(at)acm(dot)org> writes:
> > What is unclear to me in the discussion is whether or not this is
> > invalidating the item on the TODO list...
>
> No, I don't think any of this is an argument against the
> dirty-page-bitmap idea. The amount of foreground effort needed to set a
> dirty-page bit is minimal (maybe even zero, if we can make the bgwriter
> do it, though I'm pretty suspicious of that idea because I think it
> needs to be done immediately when the page is dirtied). I don't see the
> dirty-page bitmap as changing the way that VACUUM works in any
> fundamental respect --- it will just allow the vacuum process to skip
> reading pages that certainly don't need to change.
See the email I just posted. I am questioning how big a win it is to
skip heap pages if we have to sequentially scan all indexes.
> One point that does need to be considered though is what about
> anti-wraparound processing (ie, replacing old XIDs with FrozenXID before
> they wrap around)? VACUUM currently is a safe way to handle that,
> but if its normal mode of operation stops looking at every tuple then
> we're going to have an issue there.
We would need to do sequential scan occasionally and somehow track that.
--
Bruce Momjian http://candle.pha.pa.us
SRA OSS, Inc. http://www.sraoss.com
+ If your life is a hard drive, Christ can be your backup. +
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