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From: Antonin Houska <[email protected]>
To: Alvaro Herrera <[email protected]>
Cc: Marcos Pegoraro <[email protected]>
Cc: Michael Banck <[email protected]>
Cc: Junwang Zhao <[email protected]>
Cc: Kirill Reshke <[email protected]>
Cc: Pavel Stehule <[email protected]>
Cc: Michael Paquier <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: why there is not VACUUM FULL CONCURRENTLY?
Date: Mon, 03 Mar 2025 19:40:27 +0100
Message-ID: <49792.1741027227@localhost> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

Alvaro Herrera <[email protected]> wrote:

> On 2025-Feb-26, Antonin Houska wrote:
> 
> > @@ -403,39 +381,38 @@ cluster_rel(Relation OldHeap, Oid indexOid, ClusterParams *params)
> >  	 * would work in most respects, but the index would only get marked as
> >  	 * indisclustered in the current database, leading to unexpected behavior
> >  	 * if CLUSTER were later invoked in another database.
> > +	 *
> > +	 * REPACK does not set indisclustered. XXX Not sure I understand the
> > +	 * comment above: how can an attribute be set "only in the current
> > +	 * database"?
> >  	 */
> 
> Regarding this XXX comment, what's going on here is this: a CLUSTER
> command needs to remember the index that a table is clustered on.  We
> keep track of this in pg_index.indisclustered.  But pg_index is a local
> relation, not shared across databases -- so the current CLUSTER command
> can effect the update on the current database's pg_index only, not on
> other databases.  So if the user were to run CLUSTER on one database
> specifying an index, then connect to another one and expect CLUSTER
> without specifying an index to honor the previously specified index,
> that would not work.  Naturally this is only a problem for shared
> catalogs.  Not being able to handle this for shared catalogs is not a
> big loss.

Thanks for explanation. The reason I failed to understand this was probably
that I tried to imagine something worse.

-- 
Antonin Houska
Web: https://www.cybertec-postgresql.com

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