Re: Broken --dry-run mode in pg_rewind - Mailing list pgsql-hackers

From Vladimir Borodin
Subject Re: Broken --dry-run mode in pg_rewind
Date
Msg-id 17595D55-9F35-4D62-BBD3-40BDC1BFA16D@simply.name
Whole thread Raw
In response to Re: Broken --dry-run mode in pg_rewind  (Vladimir Borodin <root@simply.name>)
List pgsql-hackers

8 мая 2015 г., в 16:39, Vladimir Borodin <root@simply.name> написал(а):


8 мая 2015 г., в 16:11, Stephen Frost <sfrost@snowman.net> написал(а):

* Heikki Linnakangas (hlinnaka@iki.fi) wrote:
On 05/08/2015 03:39 PM, Michael Paquier wrote:
On Fri, May 8, 2015 at 9:34 PM, Heikki Linnakangas <hlinnaka@iki.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

Urgh, my test script had an error and I made grep only in pg_rewind.c. Sorry for noise.


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.

That would be really nice.

Added comments in all places mentioned in this thread.




Wouldn't hurt to also augment that rather doom-looking "point of no
return" comment with a note that says writes won't happen if in
dry-run. :)

For my 2c anyway.

Thanks!

Stephen


--
May the force be with you…


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May the force be with you…

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