Re: pgsql: Avoid race in RelationBuildDesc() affecting CREATE INDEX CONCURR

Hi,

On 2022-02-08 22:13:01 +0100, Tomas Vondra wrote:
> On 10/24/21 03:40, Noah Misch wrote:
> > Avoid race in RelationBuildDesc() affecting CREATE INDEX CONCURRENTLY.
> > 
> > CIC and REINDEX CONCURRENTLY assume backends see their catalog changes
> > no later than each backend's next transaction start.  That failed to
> > hold when a backend absorbed a relevant invalidation in the middle of
> > running RelationBuildDesc() on the CIC index.  Queries that use the
> > resulting index can silently fail to find rows.  Fix this for future
> > index builds by making RelationBuildDesc() loop until it finishes
> > without accepting a relevant invalidation.  It may be necessary to
> > reindex to recover from past occurrences; REINDEX CONCURRENTLY suffices.
> > Back-patch to 9.6 (all supported versions).
> > 
> > Noah Misch and Andrey Borodin, reviewed (in earlier versions) by Andres
> > Freund.
> > 
> > Discussion: https://postgr.es/m/20210730022548.GA1940096@gust.leadboat.com
> > 
> 
> Unfortunately, this seems to have broken CLOBBER_CACHE_ALWAYS builds. Since
> this commit, initdb never completes due to infinite retrying over and over
> (on the first RelationBuildDesc call).

Ugh. Do we need to do something about WRT the next set of minor releases? Is
there a a chance of this occuring in "real" workloads?

Greetings,

Andres Freund