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Re: pg_freespacemap question

From: Tatsuo Ishii <ishii(at)sraoss(dot)co(dot)jp>
To: markir(at)paradise(dot)net(dot)nz
Cc: tgl(at)sss(dot)pgh(dot)pa(dot)us, ishii(at)sraoss(dot)co(dot)jp,alvherre(at)commandprompt(dot)com, peter_e(at)gmx(dot)net,pgsql-hackers(at)postgresql(dot)org, pgsql-patches(at)postgresql(dot)org
Subject: Re: pg_freespacemap question
Date: 2006-03-11 23:40:23
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackerspgsql-patches

I have tried your patches and it worked great. Thanks.
Tatsuo Ishii
SRA OSS, Inc. Japan

> Tom Lane wrote:
> > Mark Kirkwood <markir(at)paradise(dot)net(dot)nz> writes:
> > 
> >>>Good points! I had not noticed this test case. Probably NULL is better 
> > 
> > 
> >>Would setting it to 'BLCKSZ - (fixed index header stuff)' be better, 
> > 
> > 
> > No, I don't think so, because that will just make it harder to recognize
> > what's what (remember that BLCKSZ isn't really a constant, and the index
> > overhead is not the same for all AMs either).  The point here is that
> > for indexes the FSM tracks whole-page availability, not the amount of
> > free space within pages.  So I think NULL is a reasonable representation
> > of that.  Using NULL will make it easy to filter the results if you want
> > to see only heap-page data or only index-page data, whereas it will be
> > very hard to do that if the view adopts an ultimately-artificial
> > convention about the amount of available space on an index page.
> > 
> Right - after suggesting it I realized that coding the different index
> overhead for each possible AM would have been ... difficult :-). A patch
> is attached to implement the NULL free bytes and other recommendations:
> 1/ Index free bytes set to NULL
> 2/ Comment added to the README briefly mentioning the index business
> 3/ Columns reordered more logically
> 4/ 'Blockid' column removed
> 5/ Free bytes column renamed to just 'bytes' instead of 'blockfreebytes'
> Now 5/ was only hinted at, but seemed worth doing while I was there
> (hopefully I haven't made it too terse now....).
> cheers
> Mark

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