Re: Support for REINDEX CONCURRENTLY

On 2012-12-08 21:24:47 +0900, Michael Paquier wrote:
> On Sat, Dec 8, 2012 at 2:19 AM, Andres Freund <andres(at)2ndquadrant(dot)com>wrote:
>
> > On 2012-12-07 12:01:52 -0500, Tom Lane wrote:
> > > Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> > > > On 7 December 2012 12:37, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
> > wrote:
> > > >> - There is still a problem with toast indexes. If the concurrent
> > reindex of
> > > >> a toast index fails for a reason or another, pg_relation will finish
> > with
> > > >> invalid toast index entries. I am still wondering about how to clean
> > up
> > > >> that. Any ideas?
> > >
> > > > Build another toast index, rather than reindexing the existing one,
> > > > then just use the new oid.
> >
> > Thats easier said than done in the first place. toast_save_datum()
> > explicitly opens/modifies the one index it needs and updates it.
> >
> > > Um, I don't think you can swap in a new toast index OID without taking
> > > exclusive lock on the parent table at some point.
> >
> > The whole swapping issue isn't solved satisfyingly as whole yet :(.
> >
> > If we just swap the index relfilenodes in the pg_index entries itself,
> > we wouldn't need to modify the main table's pg_class at all.
> >
> I think you are mistaking here, relfilenode is a column of pg_class and not
> pg_index.
> So whatever the method used for swapping: relfilenode switch or relname
> switch, you need to modify the pg_class entry of the old and new indexes.

The point is that with a relname switch the pg_class.oid of the index
changes. Which is a bad idea because it will possibly be referred to by
pg_depend entries. Relfilenodes - which certainly live in pg_class too,
thats not the point - aren't referred to externally though. So if
everything else in pg_class/pg_index stays the same a relfilenode switch
imo saves you a lot of trouble.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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