Re: AW: RFC: planner statistics in 7.2
От | Tom Lane |
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Тема | Re: AW: RFC: planner statistics in 7.2 |
Дата | |
Msg-id | 26094.987776244@sss.pgh.pa.us обсуждение исходный текст |
Ответ на | AW: RFC: planner statistics in 7.2 (Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>) |
Список | pgsql-hackers |
Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at> writes: >> But you don't really need to look at the index (if it even exists >> at the time you do the ANALYZE). The extent to which the data is >> ordered in the table is a property of the table, not the index. > Think compound, ascending, descending and functional index. > The (let's call it) cluster statistic for estimating indexscan cost can only > be deduced from the index itself (for all but the simplest one column btree). If you want to write code that handles those cases, go right ahead ;-). I think it's sufficient to look at the first column of a multicolumn index for cluster-order estimation --- remember all these numbers are pretty crude anyway. We have no such thing as a "descending index"; and I'm not going to worry about clustering estimation for functional indexes. regards, tom lane
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