Wierd quirk of HS/SR, probably not fixable
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From: Heikki Linnakangas on 27 Apr 2010 03:19 Josh Berkus wrote: > Here's a way to trap yourself: > > (1) Set up an HS/SR master > (2) pg_start_backup on the master > (3) clone the master to 1 or more slaves > (4) Fast shutdown the master (without pg_stop_backup) > (5) Restart the master > (6) Bring up the slaves > > Result: the slaves will come up fine in recovery mode. However, they > will never switch over to HS mode or start SR. You will not be able to > pg_stop_backup() on the master. At this point, you have no option but > to shut down the slaves and re-clone. > > The only reason why this is somewhat problematic for users is that you > will not get any messages from the master or the slaves to indicate why > they won't switch modes. So I can imagine someone wasting a lot of time > troubleshooting the wrong problems. > > Suggested resolution: I don't think there's and logical "fix" for this > case; it should just be added to the docs as a failure/troubleshooting > condition. Hmm, we could throw an error in the standby, when we see a shutdown checkpoint while we're waiting for an end-backup record. If the database was shut down before pg_stop_backup(), we know that the backup was cancelled and the end-backup record we're waiting for will never arrive. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
From: Fujii Masao on 27 Apr 2010 04:11 On Tue, Apr 27, 2010 at 4:19 PM, Heikki Linnakangas <heikki.linnakangas(a)enterprisedb.com> wrote: > Hmm, we could throw an error in the standby, when we see a shutdown > checkpoint while we're waiting for an end-backup record. If the database > was shut down before pg_stop_backup(), we know that the backup was > cancelled and the end-backup record we're waiting for will never arrive. Sounds good. This would work fine even if an immediate shutdown is done instead since the primary ends up generating a shutdown checkpoint record when restarting. Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
From: Heikki Linnakangas on 27 Apr 2010 05:25 Fujii Masao wrote: > On Tue, Apr 27, 2010 at 4:19 PM, Heikki Linnakangas > <heikki.linnakangas(a)enterprisedb.com> wrote: >> Hmm, we could throw an error in the standby, when we see a shutdown >> checkpoint while we're waiting for an end-backup record. If the database >> was shut down before pg_stop_backup(), we know that the backup was >> cancelled and the end-backup record we're waiting for will never arrive. > > Sounds good. This would work fine even if an immediate shutdown is done > instead since the primary ends up generating a shutdown checkpoint record > when restarting. Yep. I've committed a patch to do that. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
From: Robert Haas on 27 Apr 2010 07:07 On Tue, Apr 27, 2010 at 5:25 AM, Heikki Linnakangas <heikki.linnakangas(a)enterprisedb.com> wrote: > Yep. I've committed a patch to do that. Is there no way for the slave to recover from this situation? ....Robert -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
From: Fujii Masao on 27 Apr 2010 07:35
On Tue, Apr 27, 2010 at 8:07 PM, Robert Haas <robertmhaas(a)gmail.com> wrote: > On Tue, Apr 27, 2010 at 5:25 AM, Heikki Linnakangas > <heikki.linnakangas(a)enterprisedb.com> wrote: >> Yep. I've committed a patch to do that. > > Is there no way for the slave to recover from this situation? Probably Yes. You would need to take a fresh base backup and restart the slave from it. On second thought, seeing a shutdown checkpoint during waiting end-backup means mostly that the database has already reached the consistent state. We might be able to relax the error check. Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers |