Re: [WIP] Effective storage of duplicates in B-tree index.

On Thu, Mar 24, 2016 at 5:17 PM, Robert Haas <robertmhaas@gmail.com> wrote:

> On Fri, Mar 18, 2016 at 1:19 PM, Anastasia Lubennikova
> <a.lubennikova@postgrespro.ru> wrote:
> > Please, find the new version of the patch attached. Now it has WAL
> > functionality.
> >
> > Detailed description of the feature you can find in README draft
> > https://goo.gl/50O8Q0
> >
> > This patch is pretty complicated, so I ask everyone, who interested in
> this
> > feature,
> > to help with reviewing and testing it. I will be grateful for any
> feedback.
> > But please, don't complain about code style, it is still work in
> progress.
> >
> > Next things I'm going to do:
> > 1. More debugging and testing. I'm going to attach in next message
> couple of
> > sql scripts for testing.
> > 2. Fix NULLs processing
> > 3. Add a flag into pg_index, that allows to enable/disable compression
> for
> > each particular index.
> > 4. Recheck locking considerations. I tried to write code as less
> invasive as
> > possible, but we need to make sure that algorithm is still correct.
> > 5. Change BTMaxItemSize
> > 6. Bring back microvacuum functionality.
>
> I really like this idea, and the performance results seem impressive,
> but I think we should push this out to 9.7.  A btree patch that didn't
> have WAL support until two and a half weeks into the final CommitFest
> just doesn't seem to me like a good candidate.  First, as a general
> matter, if a patch isn't code-complete at the start of a CommitFest,
> it's reasonable to say that it should be reviewed but not necessarily
> committed in that CommitFest.  This patch has had some review, but I'm
> not sure how deep that review is, and I think it's had no code review
> at all of the WAL logging changes, which were submitted only a week
> ago, well after the CF deadline.  Second, the btree AM is a
> particularly poor place to introduce possibly destabilizing changes.
> Everybody depends on it, all the time, for everything.  And despite
> new tools like amcheck, it's not a particularly easy thing to debug.
>

It's all true.  But:
1) It's a great feature many users dream about.
2) Patch is not very big.
3) Patch doesn't introduce significant infrastructural changes.  It just
change some well-isolated placed.

Let's give it a chance.  I've signed as additional reviewer and I'll do my
best in spotting all possible issues in this patch.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company