Re: gistchoose vs. bloat

On Tue, Sep 11, 2012 at 10:35 AM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:

> On Tue, 2012-09-04 at 19:21 +0400, Alexander Korotkov wrote:
>
> > New version of patch is attached. Parameter "randomization" was
> > introduced. It controls whether to randomize choose. Choose algorithm
> > was rewritten.
> >
> Do you expect it to be bad in any reasonable situations? I'm inclined to
> just make it always randomize if it's better. I think it would be hard
> for a user to guess when it's better and when not.
>

Randomization should increase IO when index doesn't entirely fit to cache.
Without randomization only fraction of the tree would be used for actual
insertions. While with randomization whole tree would be potentially used
for insertions.

> Maybe it's useful to turn randomization off for testing purposes, e.g.
> to ensure determinism?
>

Yes, that's another good point. For example, randomization impede
reproducing of bugs.

------
With best regards,
Alexander Korotkov.