Re: count * performance issue

am  Thu, dem 06.03.2008, um 11:13:01 +0530 mailte sathiya psql folgendes:
> count(*) tooks much time...
> 
> but with the where clause we can make this to use indexing,... what where
> clause we can use??

An index without a WHERE can't help to avoid a seq. scan.


> 
> Am using postgres 7.4 in Debian OS with 1 GB RAM,

PG 7.4 are very old... Recent versions are MUCH faster.



> 
> am having a table with nearly 50 lakh records,
> 
> it has more than 15 columns, i want to count how many records are there, it is
> taking nearly 17 seconds to do that...
> 
> i know that to get a approximate count we can use
>          SELECT reltuples FROM pg_class where relname = TABLENAME;
> 
> but this give approximate count, and i require exact count...

There aren't a general solution. If you realy need the exact count of
tuples than you can play with a TRIGGER and increase/decrease the
tuple-count for this table in an extra table.


Andreas
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Andreas Kretschmer
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