| From: | Kevin Grittner <kgrittn(at)ymail(dot)com> |
|---|---|
| To: | Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Greg Stark <stark(at)mit(dot)edu> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, Jim Nasby <jim(at)nasby(dot)net>, Josh Berkus <josh(at)agliodbs(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: ANALYZE sampling is too good |
| Date: | 2013-12-11 19:31:44 |
| Message-ID: | 1386790304.24146.YahooMailNeo@web162906.mail.bf1.yahoo.com |
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| Lists: | pgsql-hackers |
Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz> wrote:
> For example, assume 1000 rows of 200 bytes and 1000 rows of 20 bytes,
> using 400 byte pages. In the pathologically worst case, assuming
> maximum packing density and no page has both types: the large rows would
> occupy 500 pages and the smaller rows 50 pages. So if one selected 11
> pages at random, you get about 10 pages of large rows and about one for
> small rows!
With 10 * 2 = 20 large rows, and 1 * 20 = 20 small rows.
--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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