Re: Patch: Write Amplification Reduction Method (WARM)

On Thu, Mar 30, 2017 at 11:17 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:

> On Tue, Mar 21, 2017 at 04:04:58PM -0400, Bruce Momjian wrote:
> > On Tue, Mar 21, 2017 at 04:56:16PM -0300, Alvaro Herrera wrote:
> > > Bruce Momjian wrote:
> > > > On Tue, Mar 21, 2017 at 04:43:58PM -0300, Alvaro Herrera wrote:
> > > > > Bruce Momjian wrote:
> > > > >
> > > > > > I don't think it makes sense to try and save bits and add
> complexity
> > > > > > when we have no idea if we will ever use them,
> > > > >
> > > > > If we find ourselves in dire need of additional bits, there is a
> known
> > > > > mechanism to get back 2 bits from old-style VACUUM FULL. I assume
> that
> > > > > the reason nobody has bothered to write the code for that is that
> > > > > there's no *that* much interest.
> > > >
> > > > We have no way of tracking if users still have pages that used the
> bits
> > > > via pg_upgrade before they were removed.
> > >
> > > Yes, that's exactly the code that needs to be written.
> >
> > Yes, but once it is written it will take years before those bits can be
> > used on most installations.
>
> Actually, the 2 bits from old-style VACUUM FULL bits could be reused if
> one of the WARM bits would be set when it is checked. The WARM bits
> will all be zero on pre-9.0. The check would have to be checking the
> old-style VACUUM FULL bit and checking that a WARM bit is set.
>
>
We're already doing that in the submitted patch.

Thanks,
Pavan

--
Pavan Deolasee http://www.2ndQuadrant.com/
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