Re: pg_xlogdump follow into the future - Mailing list pgsql-hackers
| From | Vladimir Rusinov |
|---|---|
| Subject | Re: pg_xlogdump follow into the future |
| Date | |
| Msg-id | CAE1wr-xKoDgfd+gaJJGeHqWXxog9uSs755CgY94xLXBRnDg9Kw@mail.gmail.com Whole thread Raw |
| In response to | Re: pg_xlogdump follow into the future (Michael Paquier <michael.paquier@gmail.com>) |
| Responses |
Re: pg_xlogdump follow into the future
|
| List | pgsql-hackers |
This patch does not have a reviewer, so I've decided to try myself on.
Disclaimer: although I review quite a lot of code daily, this is my first review for PostgreSQL. I don't know code very well, and frankly I don't really know C very well.
Hope my effort are not vain and will be helpful to somebody.
I'll be happy for review on review and any tips on process.
Summary
=======
I favour this patch. Current behaviour is indeed confusing. If we keep current behaviour we need to update docs and maybe also print a warning when using -f with a file name.
Thank you for submission, but i'm afraid there is a bit more work here:
- There is a bug, making it hard to test. Please fix.
- Please add some tests.
Submission review
==============
Patch applies cleanly on HEAD. Tests succeed.
There are no new or affected by this patch tests. Given that I've found a trivial bug (see below), a test should be created.
Usability review
============
I believe I've immediately hit a corner case:
1) I've created a new instance, started it and run `./bin/pg_xlogdump -f db/pg_wal/000000010000000000000001`.
This spewed quite a lot of stuff, as expected.
2) I've connected to the same instance and ran following:
# SELECT pg_switch_xlog();
pg_switch_xlog
----------------
0/14FA3D8
(1 row)
xlogdump immediately crashed with following:
pg_xlogdump: FATAL: could not find file "000000010000000000000002": No such file or directory
Problem is that Postgres does not create file until it's actually needed. So 000000010000000000000002 indeed was not there until after I've run some transactions. I believe same would happen after pg_start_backup(), etc.
Feature review
===========
See above. Can't do more testing.
Performance review
===============
n/a
Coding review
===========
LGTM
Architecture review
==============
n/a
--
Vladimir Rusinov
Bigtable SRE
Google Ireland Ltd.,Gordon House, Barrow Street, Dublin 4, Ireland
Registered in Dublin, Ireland
Registration Number: 368047
Registration Number: 368047
On Mon, Oct 3, 2016 at 5:44 AM, Michael Paquier <michael.paquier@gmail.com> wrote:
On Mon, Jul 18, 2016 at 8:10 PM, Magnus Hagander <magnus@hagander.net> wrote:
>
>
> On Thu, Jul 14, 2016 at 8:27 PM, Andres Freund <andres@anarazel.de> wrote:
>>
>> On 2016-07-14 13:46:23 +0200, Magnus Hagander wrote:
>> > Currently, if you run pg_xlogdump with -f, you have to specify an end
>> > position in an existing file, or if you don't it will only follow until
>> > the
>> > end of the current file.
>>
>> That's because specifying a file explicitly says that you only want to
>> look at that file, specifying two files that you want the range
>> inclusively between the two files. -f works if you just use -s.
>
>
> Hmm. It does now. I'm *sure* it didn't when I was testing it. It must've
> been something else that was broken at that point :)
Same as Andres here, my understanding is that one file means that you
just want to look at this file, and two files permits to look at a
range of changes. But I have no argument against changing the current
behavior either.
>> > I'd appreciate a review of that by someone who's done more work on the
>> > xlog
>> > stuff, but it seems trivial to me. Not sure I can argue it's a bugfix
>> > though, since the usecase simply did not work...
>>
>> I'd say it's working as intended, and you want to change that
>> intent. That's fair, but I'd not call it a bug, and I'd say it's not
>> really 9.6 material.
>
> Based on that, I agree that it's working as intended.
>
> And definitely that it's not 9.6 material.
>
> I'll stick it on the CF page so I don't forget about it.
Moved to next CF. Magnus, you may want to finish wrapping that if you
still intend to change the current behavior.
--
Michael
--
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