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Re: Index Bloat - how to tell?

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com>
Cc: Dave Crooke <dcrooke(at)gmail(dot)com>, "Plugge, Joe R(dot)" <JRPlugge(at)west(dot)com>, John W Strange <john(dot)w(dot)strange(at)jpmchase(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Index Bloat - how to tell?
Date: 2010-12-18 02:32:48
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On Thu, Dec 16, 2010 at 2:27 PM, Mladen Gogala
<mladen(dot)gogala(at)vmsinfo(dot)com> wrote:
> What is "leaf_fragmentation"? How is it defined? I wasn't able to find out
> any definition of that number. How is it calculated. I verified that running
> reindex makes it 0:

Well, according to the code:

                         * If the next leaf is on an earlier block, it means a
                         * fragmentation.
                        if (opaque->btpo_next != P_NONE &&
opaque->btpo_next < blkno)

And then the final value is calculated thus:

                snprintf(values[j++], 32, "%.2f", (double)
indexStat.fragments / (double) indexStat.leaf_pages * 100.0);

This doesn't really match my definition of the word "fragmentation", though...

Robert Haas
The Enterprise PostgreSQL Company

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