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

["Holtgrewe, Manuel" <manuel.holtgrewe@xxxxxxxxxxxxxx>]

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

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From: Holtgrewe, Manuel <manuel.holtgrewe@xxxxxxxxxxxxxx>
Sent: Tuesday, June 15, 2021 5:53:54 PM
To: Tom Lane
Cc: pgsql-general@xxxxxxxxxxxxxxxxxxxx
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@xxxxxxxxxxxxx>
Sent: Tuesday, June 15, 2021 3:39:31 PM
To: Holtgrewe, Manuel
Cc: pgsql-general@xxxxxxxxxxxxxxxxxxxx
Subject: [ext] Re: Losing data because of problematic configuration?

 

"Holtgrewe, Manuel" <manuel.holtgrewe@xxxxxxxxxxxxxx> 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