From: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
---|---|
To: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
Cc: | Vladimir Borodin <root(at)simply(dot)name>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Broken --dry-run mode in pg_rewind |
Date: | 2015-05-08 12:55:05 |
Message-ID: | 554CB229.4000207@iki.fi |
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Lists: | pgsql-hackers |
On 05/08/2015 03:39 PM, Michael Paquier wrote:
> On Fri, May 8, 2015 at 9:34 PM, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
>> On 05/08/2015 03:25 PM, Vladimir Borodin wrote:
>>> Seems, that pg_rewind does not account --dry-run option properly. A simple
>>> fix
>>> for that is attached.
>>
>>
>> No, the --dry-run takes effect later. It performs all the actions it
>> normally would, including reading files from the source, except for actually
>> writing anything in the target. See the dry-run checks in file_ops.c
>
> Even if the patch sent is incorrect, shouldn't there be some process
> bypass in updateControlFile() and createBackupLabel() in case of a
> --dry-run?
They both use open_target_file() and write_target_file(), which check
for --dry-run and do nothing if it's set.
Hmm, I wonder it we should print something else than "Done!" at the end,
if run in --dry-run mode. Or give some indication around the time it
says "Rewinding from last common checkpoint at ...", that it's running
in dry-run mode and won't actually modify anything. The progress
messages are a bit alarming if you don't realize that it's skipping all
the writes.
- Heikki
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