Re: limiting hint bit I/O

On Wed, Jan 19, 2011 at 10:44 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> Here's a new version of the patch based on some experimentation with
> ideas I posted yesterday.  At least on my Mac laptop, this is pretty
> effective at blunting the response time spike for the first table
> scan, and it converges to steady-state after about 20 tables scans.
> Rather than write every 20th page, what I've done here is make every
> 2000'th buffer allocation grant an allowance of 100 "hint bit only"
> writes.  All dirty pages and the next 100 pages that are
> dirty-only-for-hint-bits get written out.  Then we stop writing the
> dirty-only-for-hint-bits-pages until we get our next allowance of
> writes.  The idea is to try to avoid creating a lot of random writes
> on each scan through the table.  At least here, that seems to work
> pretty well - the initial scan is only about 25% slower than the
> steady state (rather than 6x or more slower).

does this only impact the scan case?  in oltp scenarios you want to
write out the bits asap, i would imagine.   what about time based
flushing, so that only x dirty hint bit pages can be written out per
time unit y?

merlin