On Tue, Mar 25, 2008 at 3:35 AM, sathiya psql <sathiya.psql@xxxxxxxxx> wrote: > Dear Friends, > I have a table with 32 lakh record in it. Table size is nearly 700 MB, > and my machine had a 1 GB + 256 MB RAM, i had created the table space in > RAM, and then created this table in this RAM. > > So now everything is in RAM, if i do a count(*) on this table it returns > 327600 in 3 seconds, why it is taking 3 seconds ????? because am sure that > no Disk I/O is happening. ( using vmstat i had confirmed, no disk I/O is > happening, swap is also not used ) > > Any Idea on this ??? > > I searched a lot in newsgroups ... can't find relevant things.... ( because > everywhere they are speaking about disk access speed, here i don't want to > worry about disk access ) > > If required i will give more information on this. Two things: - Are you VACUUM'ing regularly? It could be that you have a lot of dead rows and the table is spread out over a lot of pages of mostly dead space. That would cause *very* slow seq scans. - What is your shared_buffers set to? If it's really low then postgres could be constantly swapping from ram-disk to memory. Not much would be cached, and performance would suffer. FWIW, I did a select count(*) on a table with just over 300000 rows, and it only took 0.28 sec. Peter -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
