From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | "P(dot)J(dot) \"Josh\" Rovero" <rovero(at)sonalysts(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: TOAST performance (was Re: [GENERAL] Delete Performance) |
Date: | 2001-11-17 02:01:51 |
Message-ID: | 200111170201.fAH21q115282@candle.pha.pa.us |
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Lists: | pgsql-general pgsql-hackers |
> The "delete" took about 2 seconds. I then did it over with the
> 'value' being a 5K chunk of text, which according to octet_length
> got compressed to 3900 bytes. (This'd require two rows in the TOAST
> table.) This time the delete took 127 seconds. I was expecting
> about a 3X penalty since we needed to delete three rows not one,
> but what I got was a 60X penalty.
Wow. Can someone remind me why we take page images on delete? We
aren't really writing anything special to the page except a transction
id.
> I've worried for some time that the decision to XLOG page images was
> costing us a lot more performance than could be justified...
Is it because we take a snapshot of the page before we write it in case
we only write part of the page?
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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