Re: PostgreSQL reads each 8k block - no larger blocks are used - even on sequential scans

On Sun, Sep 27, 2009 at 06:05:51PM +0200, Gerhard Wiesinger wrote:
> A google research has shown that Gregory Stark already worked on that issue
> (see references below) but as far as I saw only on bitmap heap scans.

Greg Stark's patches are about giving the IO subsystem enough
information about where the random accesses will be ending up next.
This is important, but almost completely independent from the case
where you know you're doing sequential IO, which is what you seem to be
talking about.

> I think this is one of the most critical performance showstopper of
> PostgreSQL on the I/O side.

PG's been able to handle data as fast as it can come back from the disk
in my tests.  When you start doing calculations then it will obviously
slow down, but what you were talking about wouldn't help here either.

Then again, I don't have a particularly amazing IO subsystem.  What
sort of performance do your disks give you and at what rate is PG doing
sequential scans for you?

--
  Sam  http://samason.me.uk/