Re: [ext] Re: Losing data because of problematic configuration?

Please ignore this email. I could not reproduce it after all.

--
Dr. Manuel Holtgrewe, Dipl.-Inform.
Bioinformatician
Core Unit Bioinformatics – CUBI
Berlin Institute of Health / Max Delbrück Center for Molecular Medicine in the Helmholtz Association / Charité – Universitätsmedizin Berlin

Visiting Address: Invalidenstr. 80, 3rd Floor, Room 03 028, 10117 Berlin
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E-Mail: manuel(dot)holtgrewe(at)bihealth(dot)de
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________________________________
From: Holtgrewe, Manuel <manuel(dot)holtgrewe(at)bih-charite(dot)de>
Sent: Wednesday, June 16, 2021 10:54:49 AM
To: Tom Lane
Cc: pgsql-general(at)lists(dot)postgresql(dot)org
Subject: Re: [ext] Re: Losing data because of problematic configuration?

Hi again,

thank you for pinpointing the issue.

I have now updated the table with "ALTER TABLE $table SET LOGGED" (actually it's a partitioned table and I've altered both the main table and the partitions).

I wanted to double-check the result and what I found out using "select relpersistence, relname from pg_class" that, e.g., ${table_name}_383_pkey still has its relpersistence set to "u" whereas ${table_name}_383 has its relpersistence set to "p" now.

Does anyone have an idea what I'm doing wrong here?

Thank you!

Manuel

________________________________
From: Holtgrewe, Manuel <manuel(dot)holtgrewe(at)bih-charite(dot)de>
Sent: Tuesday, June 15, 2021 5:53:54 PM
To: Tom Lane
Cc: pgsql-general(at)lists(dot)postgresql(dot)org
Subject: Re: [ext] Re: Losing data because of problematic configuration?

>> < 2021-06-15 12:33:04.537 CEST > DEBUG: resetting unlogged relations: cleanup 1 init 0
>
> Are you perhaps keeping your data in an UNLOGGED table? If so, resetting
> it to empty after a crash is exactly what's supposed to happen. The
> entire point of UNLOGGED is that the performance benefits come at the
> cost of losing the data on crash.

D'oh!

Yes, that is the case. I once used this but I was convinced that I took this back in some version. It is not in my main deployment, though. Now I have to find out (a) why I have diverging deployment and (b) how that bug came about to be.

Thanks a lot!

________________________________
From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Sent: Tuesday, June 15, 2021 3:39:31 PM
To: Holtgrewe, Manuel
Cc: pgsql-general(at)lists(dot)postgresql(dot)org
Subject: [ext] Re: Losing data because of problematic configuration?

"Holtgrewe, Manuel" <manuel(dot)holtgrewe(at)bih-charite(dot)de> writes:
> So it looks as if the database jumps back "half an hour" to ensure consistent data. Everything in between is lost.

Postgres does not lose committed data --- if it did, we'd consider that a
fairly serious bug. (Well, there are caveats of course. But most of them
have to do with operating-system crashes or power loss, neither of which
are at stake here.)

I am wondering about this though:

> < 2021-06-15 12:33:04.537 CEST > DEBUG: resetting unlogged relations: cleanup 1 init 0

Are you perhaps keeping your data in an UNLOGGED table? If so, resetting
it to empty after a crash is exactly what's supposed to happen. The
entire point of UNLOGGED is that the performance benefits come at the
cost of losing the data on crash.

regards, tom lane