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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Pavel Rotek <pavel.rotek@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Toast space grows
Date: Fri, 07 Mar 2008 09:31:23 -0500
Message-ID: <13188.1204900283@sss.pgh.pa.us> (raw)
In-Reply-To: <3556c08c0803070611p542eb317vfaf9b783172b6c3@mail.gmail.com>
References: <3556c08c0803070035p6d8b4aa8m6318f54728f61022@mail.gmail.com>
	<47D10722.4080508@archonet.com>
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	<20080307065314.1248665b.wmoran@collaborativefusion.com>
	<3556c08c0803070459i8598423t64e0704e48af533@mail.gmail.com>
	<11848.1204896799@sss.pgh.pa.us>
	<3556c08c0803070611p542eb317vfaf9b783172b6c3@mail.gmail.com>

"Pavel Rotek" <pavel.rotek@gmail.com> writes:
> 2008/3/7, Tom Lane <tgl@sss.pgh.pa.us>:
>> You mean that you build up the 5MB log entry by adding a few lines at a
>> time?  That's going to consume horrid amounts of toast space, because
>> each time you add a few lines, an entire new toasted field value is
>> created.

> well, this will be the main problem... But... do uncomitted trasactions
> affect toast space?

Sure.  Where do you think the data goes?  It's gotta be stored
someplace.  Every UPDATE operation that changes a toasted field will
consume space for a fresh copy of that field, whether it ever commits or
not.  You need VACUUM to reclaim the space eaten by no-longer-accessible
copies.

			regards, tom lane

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