Re: [TODO] Track number of files ready to be archived in pg_stat_archiver

Le 25/08/2014 19:00, Gilles Darold a écrit :
> Le 21/08/2014 10:17, Julien Rouhaud a écrit :
>> Hello,
>>
>> Attached patch implements the following TODO item :
>>
>> Track number of WAL files ready to be archived in pg_stat_archiver
>>
>> However, it will track the total number of any file ready to be
>> archived, not only WAL files.
>>
>> Please let me know what you think about it.
>>
>> Regards.
>
> Hi,
>
> Maybe looking at archive ready count will be more efficient if it is
> done in the view definition through a function. This will avoid any
> issue with incrementing/decrement of archiverStats.ready_count and the
> patch will be more simple. Also I don't think we need an other memory
> allocation for that, the counter information is always in the number of
> .ready files in the archive_status directory and the call to
> pg_stat_archiver doesn't need high speed performances.
>
> For example having a new function called
> pg_stat_get_archive_ready_count() that does the same at what you add
> into pgstat_read_statsfiles() and the pg_stat_archiver defined as follow:
>
> CREATE VIEW pg_stat_archiver AS
>     s.failed_count,
>     s.last_failed_wal,
>     s.last_failed_time,
>     pg_stat_get_archive_ready() as ready_count,
>     s.stats_reset
> FROM pg_stat_get_archiver() s;
>
> The function pg_stat_get_archive_ready_count() will also be available
> for any other querying.
>

Indeed, this approach should be more efficient. It also avoid unexpected
results, like if someone has the bad idea to remove a .ready file in
pg_xlog/archive_status directory.

Attached v2 patch implements this approach. All the work is still done
in pg_stat_get_archiver, as I don't think that having a specific
function for that information would be really interesting.
--
Julien Rouhaud
http://dalibo.com - http://dalibo.org