Re: [v9.3] Extra Daemons (Re: elegant and effective way for running jobs inside a database)

2012-04-25 11:40 keltezéssel, Kohei KaiGai írta:
> 2012/3/10 Simon Riggs <simon@2ndquadrant.com>:
>> On Fri, Mar 9, 2012 at 6:51 PM, Andrew Dunstan <andrew@dunslane.net> wrote:
>>>
>>> On 03/09/2012 01:40 PM, Robert Haas wrote:
>>>> On Fri, Mar 9, 2012 at 12:02 PM, David E. Wheeler<david@justatheory.com>
>>>>   wrote:
>>>>> On Mar 9, 2012, at 7:55 AM, Merlin Moncure wrote:
>>>>>> 100% agree  (having re-read the thread and Alvaro's idea having sunk
>>>>>> in).  Being able to set up daemon processes side by side with the
>>>>>> postmaster would fit the bill nicely.  It's pretty interesting to
>>>>>> think of all the places you could go with it.
>>>>> pgAgent could use it *right now*. I keep forgetting to restart it after
>>>>> restarting PostgreSQL and finding after a day or so that no jobs have run.
>>>> That can and should be fixed by teaching pgAgent that failing to
>>>> connect to the server, or getting disconnected, is not a fatal error,
>>>> but a reason to sleep and retry.
>>>
>>> Yeah. It's still not entirely clear to me what a postmaster-controlled
>>> daemon is going to be able to do that an external daemon can't.
>> Start and stop at the same time as postmaster, without any pain.
>>
>> It's a considerable convenience to be able to design this aspect once
>> and then have all things linked to the postmaster follow that. It
>> means people will be able to write code that runs on all OS easily,
>> without everybody having similar but slightly different code about
>> starting up, reading parameters, following security rules etc.. Tight
>> integration, with good usability.
>>
> I tried to implement a patch according to the idea. It allows extensions
> to register an entry point of the self-managed daemon processes,
> then postmaster start and stop them according to the normal manner.
>
> [kaigai@iwashi patch]$ ps ax | grep postgres
> 27784 pts/0    S      0:00 /usr/local/pgsql/bin/postgres
> 27786 ?        Ss     0:00 postgres: writer process
> 27787 ?        Ss     0:00 postgres: checkpointer process
> 27788 ?        Ss     0:00 postgres: wal writer process
> 27789 ?        Ss     0:00 postgres: autovacuum launcher process
> 27790 ?        Ss     0:00 postgres: stats collector process
> 27791 ?        Ss     0:00 postgres: auth_counter              <== (*)
>
> The auth_counter being included in this patch is just an example of
> this functionality. It does not have significant meanings. It just logs
> number of authentication success and fails every intervals.
>
> I'm motivated to define an extra daemon that attach shared memory
> segment of PostgreSQL as a computing server to avoid limitation of
> number of GPU code that we can load concurrently.
>
> Thanks,

I have tested this original version. The patch has a single trivial reject,
after fixing it, it compiled nicely.

After adding shared_preload_libraries='$libdir/auth_counter', the extra
daemon start and stops nicely with pg_ctl start/stop. The auth_counter.c
code is a fine minimalistic example on writing one's own daemon.

Thanks,
Zoltán Böszörményi

--
----------------------------------
Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt, Austria
Web: http://www.postgresql-support.de     http://www.postgresql.at/