Skip site navigation (1) Skip section navigation (2)

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: AANLkTikedY0=mBZ4nFm3XQK=u08j59yqPMsrsJqA=fgP@mail.gmail.com (view raw or flat)
Thread:
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)
                                indexStat.fragments++;

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
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

In response to

Responses

pgsql-performance by date

Next:From: Robert HaasDate: 2010-12-18 02:46:55
Subject: Re: Strange optimization - xmin,xmax compression :)
Previous:From: Scott MarloweDate: 2010-12-18 02:06:15
Subject: Re: Compared MS SQL 2000 to Postgresql 9.0 on Windows

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group