Re: Bugs in CREATE/DROP INDEX CONCURRENTLY

On Thu, Nov 29, 2012 at 8:52 AM, Andres Freund <andres@2ndquadrant.com>wrote:

> On 2012-11-28 18:41:39 -0500, Tom Lane wrote:
> > Andres Freund <andres@anarazel.de> writes:
> > > On 2012-11-28 17:42:18 -0500, Tom Lane wrote:
> > >> I agree it's a judgment call, though.  Anybody want to argue for the
> > >> other position?
> >
> > > Hm. Seems odd to include indexes that are being dropped concurrently at
> > > that moment. But then, we can't really detect that situation and as you
> > > say its consistent with pg_dump...
> >
> > [ thinks about that for a bit... ]  We could have that, for about the
> same
> > cost as the currently proposed patch: instead of defining the added flag
> > column as "index is live", define it as "drop in progress", and set it
> > immediately at the start of the DROP CONCURRENTLY sequence.  Then the
> > "dead" condition that RelationGetIndexList must check for is "drop in
> > progress and not indisvalid and not indisready".
>
> You're right.
>
> > However, this is more complicated and harder to understand.  So unless
> > somebody is really excited about being able to tell the difference
> > between create-in-progress and drop-in-progress, I'd rather leave the
> > patch as-is.
>
> The only real argument for doing this that I can see is a potential
> REINDEX CONCURRENTLY.
>
Patch that has been submitted to this commit fest, and is going to need a
lot of rework as well as more infrastructure like a better MVCC-ish
SnapshotNow.
-- 
Michael Paquier
http://michael.otacoo.com