Re: postgresql is slow with larger table even it is in RAM

On Tuesday 25 March 2008, sathiya psql 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.

I can't really say anything about your RAM issue, but count(*) is always a bad
idea if it can be avoided. Assuming you have a primary key on the table, do a
count(pk). In my experience that alone cuts down up to 30% of execution time.

Uwe