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From: Alvaro Herrera <[email protected]>
To: Antonin Houska <[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: Fri, 31 Jan 2025 11:29:22 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <24725.1738318524@antos>

On 2025-Jan-31, Antonin Houska wrote:

> Alvaro Herrera <[email protected]> wrote:
> 
> > Something that Robert Haas just mentioned to me is handling of row
> > locks: if concurrent transactions are keeping rows in the original table
> > locked (especially SELECT FOR KEY SHARE, since that's not considered by
> > logical decoding at present and it would be possible to break foreign
> > keys if we just do nothing), them we need these to be "transferred" to
> > the new table somehow.
> 
> The current implementation acquires AccessExclusiveLock on the table
> (supposedly for very short time) so it can swap the table and index
> files. Once we have that lock, I think the transactions holding the row locks
> should no longer be running. Or can the row lock "survive" the table lock
> somehow?

Oh right, I forgot about this step.  That seems like it should be
sufficient to protect against that problem.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
Al principio era UNIX, y UNIX habló y dijo: "Hello world\n".
No dijo "Hello New Jersey\n", ni "Hello USA\n".

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