Обсуждение: Access to old versions of a row

As long as the vacuum is not run, older versions of a given row should
be "somewhere". Is there a way to read them?

Thanks

    matthias
-- 
Matthias Apitz, ✉ guru@unixarea.de, http://www.unixarea.de/ +49-176-38902045
Public GnuPG key: http://www.unixarea.de/key.pub

On 10/8/23 16:25, Matthias Apitz wrote:
> 
> As long as the vacuum is not run, older versions of a given row should
> be "somewhere". Is there a way to read them?

No.

But there is a pg_dirtyread extension that can do it. 
https://github.com/df7cb/pg_dirtyread
-- 
Vik Fearing

On 2023-Oct-08, Matthias Apitz wrote:

> 
> As long as the vacuum is not run, older versions of a given row should
> be "somewhere". Is there a way to read them?

Maybe with 
https://github.com/df7cb/pg_dirtyread

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/

Hi,

On 2023-10-08 21:35:15 +0200, Vik Fearing wrote:
> On 10/8/23 16:25, Matthias Apitz wrote:
> > 
> > As long as the vacuum is not run, older versions of a given row should
> > be "somewhere". Is there a way to read them?

(auto-)vacuum not having processed a table doesn't guarantee that row versions
have not been removed. Most importantly, on-access pruning can lead to row
versions being removed.  There's also the issue that the toast table could
have been autovacuumed independently from the "main" table.


> No.
> 
> But there is a pg_dirtyread extension that can do it.
> https://github.com/df7cb/pg_dirtyread

Note that there's a lot of potential for bogus data and even crashes when
using something like this. Which is fine when used for data recovery purposes,
but not for many other potential usecases.

Greetings,

Andres Freund