Re: Patch: Write Amplification Reduction Method (WARM)

On 30 March 2017 at 16:50, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, Mar 30, 2017 at 11:41 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>> On 2017-03-30 16:43:41 +0530, Pavan Deolasee wrote:
>>> Looks like OID conflict to me.. Please try rebased set.
>>
>> Pavan, Alvaro, everyone: I know you guys are working very hard on this,
>> but I think at this point it's too late to commit this for v10. This is
>> patch that's affecting the on-disk format, in quite subtle
>> ways. Committing this just at the end of the development cyle / shortly
>> before feature freeze, seems too dangerous to me.
>>
>> Let's commit this just at the beginning of the cycle, so we have time to
>> shake out the bugs.
>
> +1, although I think it should also have substantially more review first.

So Andres says defer this, but Robert says "more review", which is
more than just deferral.

We have some risky things in this release such as Hash Indexes,
function changes. I perfectly understand that perception of risk is
affected significantly by whether you wrote something or not. Andres
and Robert did not write it and so they see problems. I confess that
those two mentioned changes make me very scared and I'm wondering
whether we should disable them. Fear is normal.

A risk perspective is a good one to take. What I think we should do is
strip out the areas of complexity, like TOAST to reduce the footprint
and minimize the risk. There is benefit in WARM and PostgreSQL has
received public critiscism around our performance in this area. This
is more important than just a nice few % points of performance.

The bottom line is that this is written by Pavan, the guy we've
trusted for a decade to write and support HOT. We all know he can and
will fix any problems that emerge because he has shown us many times
he can and does.

We also observe that people from the same company sometimes support
their colleagues when they should not. I see no reason to believe that
is influencing my comments here.

The question is not whether this is ready today, but will it be
trusted and safe to use by Sept. Given the RMT, I would say yes, it
can be.

So I say we should commit WARM in PG10, with some restrictions.

--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services