Re: How to improve db performance with $7K?

Dave Cramer <pg(at)fastcrypt(dot)com> writes:

> PFC wrote:
> >
> > My Laptop does 19 MB/s (reading <10 KB files, reiser4) !
>
> Yeah, 35Mb per sec is slow for a raid controller, the 3ware mirrored is
> about 50Mb/sec, and striped is about 100

Well you're comparing apples and oranges here. A modern 7200rpm drive should
be capable of doing 40-50MB/s depending on the location of the data on the
disk.

But that's only doing sequential access of data using something like dd and
without other processes intervening and causing seeks. In practice it seems a
busy databases see random_page_costs of about 4 which for a drive with 10ms
seek time translates to only about 3.2MB/s.

I think the first order of business is getting pg_xlog onto its own device.
That alone should remove a lot of the seeking. If it's an ext3 device I would
also consider moving the journal to a dedicated drive as well. (or if they're
scsi drives or you're sure the raid controller is safe from write caching then
just switch file systems to something that doesn't journal data.)

--
greg