Re: pg_upgrade and rsync

6 марта 2015 г., в 6:11, Bruce Momjian <bruce@momjian.us> написал(а):

On Thu, Mar  5, 2015 at 10:55:28AM +0300, Vladimir Borodin wrote:

   You are correct that a pg_controldata file is copied over that has
   wal_level=minimal, but that should not be a problem.


I suppose, this is the root cause of why replica does not start as hot standby.
It it enough to start it as warm standby, but not hot standby.
See CheckRequiredParameterValues function in xlog.c which is called inside of
StartupXLOG function.

Yes, you are correct.  I spent all day building a test harness so I
could automate this setup and test various failures.  I was able to
reproduce your failure, and you are correct that the proper fix is to
set wal_level=hot_standby on the new master, and then start and stop the
new cluster just before rsync.

The root cause is that pg_upgrade calls pg_resetxlog -o on the new
cluster _after_ the new cluster stopped for the final time, so rsync is
copying the incorrect pg_controldata wal_level value.  Also, even if
pg_resetxlog preserved wal_level in the control file, there is no
guarantee that the user configured the new cluster's wal_level for
hot_standby anyway.

What I have done is to update the pg_upgrade instructions to add this
required step.  Updated doc patch attached.  (I also added the --delete
flag to rsync.)  Thanks so much for your detailed report.

       But it could not be done with --size-only key, because control-file is
       of fixed
       size and rsync would skip it. Or may be everything should be copied
       with
       --size-only and control-file should be copied without this option.


   Well, what happens is that there is no _new_ standby pg_controldata
   file, so it is copied fully from the new master.  Are you running initdb
   to create the new standby --- you shouldn't be doing that as the rsync
   will do that for you.  


No, I don’t. The scenario of the problem with copying control-file was in case
when I:
1. ran pg_upgrade on master and got control-file with "wal_level = minimal",
2. did rsync --size-only to replica (and it got this control-file with
"wal_level = minimal"),
3. started and stopped postgres on master to get «good» control-file with
"wal_level = hot_standby»,
4. did rsync --size-only to replica one more time. And this time control-file
is not copied because of the same size of control-file.

Actually, if you don’t do step 2, everything works as expected. Sorry for
bothering you.

Ah, yes, I think doing rsync twice is never a good suggestion.  It can
lead to too many failures.  Doing the start/stop before rsync seems like
the best solution.

--
 Bruce Momjian  <bruce@momjian.us>        http://momjian.us
 EnterpriseDB                             http://enterprisedb.com

 + Everyone has their own god. +
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