From: | Michael Paquier <michael(at)paquier(dot)xyz> |
---|---|
To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
Cc: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: PANIC during crash recovery of a recently promoted standby |
Date: | 2018-05-11 22:41:33 |
Message-ID: | 20180511224133.GA1891@paquier.xyz |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On Fri, May 11, 2018 at 12:09:58PM -0300, Alvaro Herrera wrote:
> Yeah, I had this exact comment, but I was unable to come up with a test
> case that would cause a problem.
pg_ctl promote would wait for the control file to be updated, so you
cannot use it in the TAP tests to trigger the promotion. Still I think
I found one after waking up? Please note I have not tested it:
- Use a custom trigger file and then trigger promotion with a signal.
- Use a sleep command in recovery_end_command to increase the window, as
what matters is sleeping after CreateEndOfRecoveryRecord updates the
control file.
- Issue a restart point on the standby, which will update the control
file.
- Stop the standby with immediate mode.
- Start the standby, it should see unreferenced pages.
> Hmm. Can we change the control file in released branches? (It should
> be possible to make the new server understand both old and new formats,
> but I think this is breaking new ground and it looks easy to introduce
> more bugs there.)
We definitely can't, even if the new value is added at the end of
DBState :(
A couple of wild ideas, not tested, again after waking up:
1) We could also abuse of existing values by using the existing
DB_IN_CRASH_RECOVERY or DB_STARTUP. Still that's not completely true as
the cluster may be open for business as a hot standby.
2) Invent a new special value for XLogRecPtr, normally impossible to
reach, which uses high bits.
--
Michael
From | Date | Subject | |
---|---|---|---|
Next Message | Justin Pryzby | 2018-05-12 00:38:46 | allow psql to watch \dt |
Previous Message | Andres Freund | 2018-05-11 22:32:04 | Re: Having query cache in core |