From: | Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com> |
---|---|
To: | Peter <pmc(at)citylink(dot)dinoex(dot)sub(dot)org>, pgsql-general(at)lists(dot)postgresql(dot)org |
Subject: | Re: Something else about Redo Logs disappearing |
Date: | 2020-06-09 04:21:47 |
Message-ID: | c5ae78f9-e922-29bc-379d-739baeb06e2f@aklaver.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-general |
On 6/8/20 7:33 PM, Peter wrote:
>
> Actually, the affair had some good side: as usual I was checking
> my own designs first and looking for flaws, and indeed I found one:
>
> If you do copy out the archive logs not directly to tape, but to
> some disk area for further processing, then there is an issue with
> possible loss. If you do it like the docs say, with a command like
> this:
>
> archive_command = 'test ! -f /mnt/server/archivedir/%f && cp %p
> +/mnt/server/archivedir/%f' # Unix
>
> That "cp" is usually not synchronous. So there is the possibility
> that this command terminates successfully, and reports exitcode zero
> back to the Postgres, and then the Postgres will consider that log
> being safely away.
Which is why just following the above command in the docs is:
"(This is an example, not a recommendation, and might not work on all
platforms.) "
Generally for peace of mind folks use third party tools like:
pg_backrest(https://pgbackrest.org/),
pg_probackup(https://postgrespro.com/products/extensions/pg_probackup)
or Barman(https://www.pgbarman.org/).
as they offer safety checks for your backups.
I use pg_backrest, but it does not look promising for running on BSD:
https://fluca1978.github.io/2019/03/04/pgbackrest_FreeBSD.html
Not sure about pg_probackup.
Barman is Python package:
http://docs.pgbarman.org/release/2.10/#installation-from-sources
>
> But the target of the copy may not yet been written to disk. If
> at that point a power loss happens, the log may become missing/damaged/
> incomplete, while the database may or may not consider it done
> when restarting.
>
> Therefore, mounting such a target filesystem in all-synchronous mode
> might be a good idea. (UFS: "-o sync", ZFS: "set sync=always")
>
> cheerio,
> PMc
>
>
--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com
From | Date | Subject | |
---|---|---|---|
Next Message | Tom Lane | 2020-06-09 05:27:20 | Re: Something else about Redo Logs disappearing |
Previous Message | Peter | 2020-06-09 02:33:26 | Re: Something else about Redo Logs disappearing |