Hi Horiguchi-san,
(Why me?)
Because the story was also related to PG-REX, which you are
also involved in developing. Perhaps off-list instead of
-hackers would have been better, but I emailed -hackers because
the same problem could be encountered by PostgreSQL users who
do not use PG-REX.
In a project I helped with, I encountered an issue where
the archive command kept failing. I thought this issue was
related to the problem in this thread, so I'm sharing it here.
If I should create a new thread, please let me know.
* Problem
- The archive_command is failed always.
Although I think the configuration is a kind of broken, it can be seen
as it is mimicing the case of shared-archive, where primary and
standby share the same archive directory.
To be precise, the environment of this reproduction script is
different from our actual environment. I tried to make it as
simple as possible to reproduce the problem.
(In order to make it look like the actual environment, you have
to build a PG-REX environment.)
A simple replication environment might be enough, so I'll try to
recreate a script that is closer to the actual environment later.
Basically we need to use an archive command like the following for
that case to avoid this kind of failure. The script returns "success"
when the target file is found but identical with the source file. I
don't find such a description in the documentation, and haven't
bothered digging into the mailing-list archive.
==
#! /bin/bash
if [ -f $2 ]; then
cmp -s $1 $2
if [ $? != 0 ]; then
exit 1
fi
exit 0
fi
cp $1 $2
==
Thanks for your reply.
Since the above behavior is different from the behavior of the
test command in the following example in postgresql.conf, I think
we should write a note about this example.
# e.g. 'test ! -f /mnt/server/archivedir/%f && cp %p /mnt/server/archivedir/%f'
Let me describe the problem we faced.
- When archive_mode=always, archive_command is (sometimes) executed
in a situation where the history file already exists on the standby
side.
- In this case, if "test ! -f" is written in the archive_command of
postgresql.conf on the standby side, the command will keep failing.
Note that this problem does not occur when archive_mode=on.
So, what should we do for the user? I think we should put some notes
in postgresql.conf or in the documentation. For example, something
like this:
====
Note: If you use archive_mode=always, the archive_command on the standby side should not
be used "test ! -f".
====
Regards,
Tatsuro Yamada
