Re: *sigh*
От | Mark Kirkwood |
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Тема | Re: *sigh* |
Дата | |
Msg-id | 3FCD9ED4.1000108@paradise.net.nz обсуждение исходный текст |
Ответ на | Re: *sigh* (Christopher Browne <cbbrowne@acm.org>) |
Ответы |
Re: *sigh*
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Список | pgsql-hackers |
How about: Implement a function "estimated_count" that can be used instead of "count". It could use something like the algorithm in src/backend/commands/analyze.c to get a reasonably accurate psuedo count quickly. The advantage of this approach is that "count" still means (exact)count (for your xact snapshot anyway). Then the situation becomes: Want a fast count? - use estimated_count(*) Want an exact count - use count(*) regards Mark Christopher Browne wrote: >For a small table, it will be cheaper to walk through and calculate >count(*) directly from the tuples themselves. > >The situation where it may be worthwhile to do this is a table which >is rather large (thus count(*) is expensive) where there is some >special reason to truly care how many rows there are in the table. >For _most_ tables, it seems unlikely that this will be true. For >_most_ tables, it is absolutely not worth the cost of tracking the >information. > >
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