Re: Proposed LogWriter Scheme, WAS: Potential Large

On Sun, 2002-10-06 at 04:03, Tom Lane wrote:
> Hannu Krosing <hannu(at)tm(dot)ee> writes:
> > Or its solution ;) as instead of the predicting we just write all data
> > in log that is ready to be written. If we postpone writing, there will
> > be hickups when we suddenly discover that we need to write a whole lot
> > of pages (fsync()) after idling the disk for some period.
>
> This part is exactly the same point that I've been proposing to solve
> with a background writer process. We don't need aio_write for that.
> The background writer can handle pushing completed WAL pages out to
> disk. The sticky part is trying to gang the writes for multiple
> transactions whose COMMIT records would fit into the same WAL page,
> and that WAL page isn't full yet.

I just hoped that kernel could be used as the background writer process
and in the process also solve the multiple commits on the same page
problem

> The rest of what you wrote seems like wishful thinking about how
> aio_write might behave :-(. I have no faith in it.

Yeah, and the fact that there are several slightly different
implementations of AIO even on Linux alone does not help.

I have to test the SGI KAIO implementation for conformance with my
wishful thinking ;)

Perhaps you could ask around about AIO in RedHat Advanced Server (is it
the same AIO as SGI, how does it behave in "multiple writes on the same
page" case) as you may have better links to RedHat ?

--------------
Hannu