Re: should we set hint bits without dirtying the page?

On Thu, 2010-12-02 at 19:00 -0500, Robert Haas wrote:
> Untidy buffers would be treated as dirty by the background writer
> cleaning scan, but as clean by checkpoints and by backends doing
> emergency buffer cleaning to feed new allocations.

Differentiating between a backend write and a bgwriter write sounds like
a good heuristic to me. Of course, only numbers can tell, but it sounds
promising.

> I then got to wondering whether we should even go a step further, and
> simply decree that a page with only hint bit updates is not dirty and
> won't be written, period.

Sounds reasonable.

Just to throw another idea out there, perhaps we could change the
behavior based on whether the page is already dirty or not. I haven't
thought this through, but it might be an interesting approach.

Regards,
Jeff Davis