Re: Incorrect assumptions with low LIMITs
От
Jeff Davis
Тема
Re: Incorrect assumptions with low LIMITs
Дата
Msg-id
1331933968.5271.127.camel@sussancws0025
Ответ на
Incorrect assumptions with low LIMITs (Simon Riggs)
Список
Дерево обсуждения
Incorrect assumptions with low LIMITs Simon Riggs <simon@2ndQuadrant.com>
Re: Incorrect assumptions with low LIMITs Jeff Davis <pgsql@j-davis.com>
Re: Incorrect assumptions with low LIMITs Simon Riggs <simon@2ndQuadrant.com>
Re: Incorrect assumptions with low LIMITs Tom Lane <tgl@sss.pgh.pa.us>
Re: Incorrect assumptions with low LIMITs Simon Riggs <simon@2ndquadrant.com>
Re: Incorrect assumptions with low LIMITs Greg Stark <stark@mit.edu>
Re: Incorrect assumptions with low LIMITs Simon Riggs <simon@2ndQuadrant.com>
Re: Incorrect assumptions with low LIMITs Jeff Davis <pgsql@j-davis.com>
Re: Incorrect assumptions with low LIMITs Daniel Farina <daniel@heroku.com>
On Fri, 2012-03-16 at 18:25 +0000, Simon Riggs wrote: > Any time we apply a LIMIT clause to a plan with a SeqScan or > unqualified IndexScan, we shouldn't assume the scan will do less than > say 10% of the table. It might, but its an unsafe assumption because > as the selectivity decreases so does the safety of the assumption that > rows are uniformly distributed. Just trying to follow along. You mean "as the selectivity _increases_ the safety of the assumption that the rows are uniformly distributed decreases", right? Regards,Jeff Davis
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