First off, this is posted to the wrong list -- this list is for
discussion of development of the PostgreSQL product. There is a
list for performance questions where this belongs:
pgsql-performance@postgresql.org. I'm moving this to the
performance list with a blind copy to the -hackers list so people
know where the discussion went.
Nick Raj <nickrajjain@gmail.com> wrote:
> When i execute the query first time, query takes a quite longer
> time but second time execution of the same query takes very less
> time (despite execution plan is same)
> Why the same plan giving different execution time? (Reason may be
> data gets buffered (cached) for the second time execution) Why
> there is so much difference?
Because an access to a RAM buffer is much, much faster than a disk
access.
> Which option will be true?
It depends entirely on how much of the data needed for the query is
cached. Sometimes people will run a set of queries to "warm" the
cache before letting users in.
> MY postgresql.conf file having setting like this (this is original
> setting, i haven't modify anything)
> shared_buffers = 28MB
> #work_mem = 1MB # min 64kB
> #maintenance_work_mem = 16MB # min 1MB
If you're concerned about performance, these settings (and several
others) should probably be adjusted:
http://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server
-Kevin
