Re: Seqscan in MAX(index_column)
От | Neil Conway |
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Тема | Re: Seqscan in MAX(index_column) |
Дата | |
Msg-id | 1062728210.360.14.camel@tokyo обсуждение исходный текст |
Ответ на | Re: Seqscan in MAX(index_column) (Bruce Momjian <pgman@candle.pha.pa.us>) |
Ответы |
Re: Seqscan in MAX(index_column)
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Список | pgsql-hackers |
On Thu, 2003-09-04 at 22:02, Bruce Momjian wrote: > My idea is that if a transaction doing a COUNT(*) would first look to > see if there already was a visible cached value, and if not, it would do > the COUNT(*) and insert into the cache table. Any INSERT/DELETE would > remove the value from the cache. As I see it, the commit of the > INSERT/DELETE transaction would then auto-invalidate the cache at the > exact time the transaction commits. This would allow MVCC visibility of > the counts. But this means that some of the time (indeed, *much* of the time), COUNT(*) would require a seqscan of the entire table. Since at many sites that will take an enormous amount of time (and disk I/O), that makes this solution infeasible IMHO. In general, I don't think this is worth doing. -Neil
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