Re: [HACKERS] Proposal: Improve bitmap costing for lossy pages

On Wed, Aug 30, 2017 at 2:00 AM, Robert Haas <robertmhaas@gmail.com> wrote:

>
> I suggest defining a TBM_FILLFACTOR constant instead of repeating the
> value 0.9 in a bunch of places.  I think it would also be good to try
> to find the sweet spot for that constant.  Making it bigger reduces
> the number of lossy entries  created, but making it smaller reduces
> the number of times we have to walk the bitmap.  So if, for example,
> 0.75 is sufficient to produce almost all of the gain, then I think we
> would want to prefer 0.75 to 0.9.  But if 0.9 is better, then we can
> stick with that.
>
> Note that a value higher than 0.9375 wouldn't be sane without some
> additional safety precautions because maxentries could be as low as
> 16.

Thanks for the feedback.  I will work on it.

>
> --
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company



-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com