Re: [HACKERS] Index corruption with CREATE INDEX CONCURRENTLY

Hi,

On 2017-02-05 16:37:33 -0800, Andres Freund wrote:
> >  RelationGetIndexList(Relation relation)
> > @@ -4746,8 +4747,10 @@ RelationGetIndexPredicate(Relation relat
> >   * we can include system attributes (e.g., OID) in the bitmap representation.
> >   *
> >   * Caller had better hold at least RowExclusiveLock on the target relation
> > - * to ensure that it has a stable set of indexes.  This also makes it safe
> > - * (deadlock-free) for us to take locks on the relation's indexes.
> > + * to ensure it is safe (deadlock-free) for us to take locks on the relation's
> > + * indexes.  Note that since the introduction of CREATE INDEX CONCURRENTLY,
> > + * that lock level doesn't guarantee a stable set of indexes, so we have to
> > + * be prepared to retry here in case of a change in the set of indexes.
> 
> I've not yet read the full thread, but I'm a bit confused so far. We
> obviously can get changing information about indexes here, but isn't
> that something we have to deal with anyway?  If we guarantee that we
> don't loose knowledge that there's a pending invalidation, why do we
> have to retry?  Pretty much by definition the knowledge in a relcache
> entry can be outdated as soon as returned unless locking prevents that
> from being possible - which is not the case here.
> 
> ISTM it'd be better not to have retry logic here, but to follow the more
> general pattern of making sure that we know whether the information
> needs to be recomputed at the next access.  We could either do that by
> having an additional bit of information about the validity of the
> bitmaps (so we have invalid, building, valid - and only set valid at the
> end of computing the bitmaps when still building and not invalid again),
> or we simply move the bitmap computation into the normal relcache build.

To show what I mean here's an *unpolished* and *barely tested* patch
implementing the first of my suggestions.

Alvaro, Pavan, I think should address the issue as well?

- Andres

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