Re[2]: [HACKERS] Re[2]: [HACKERS] Connect from background worker thread to database

Понедельник, 25 ноября 2013, 8:31 +09:00 от Michael Paquier <michael(dot)paquier(at)gmail(dot)com>:
>On Mon, Nov 25, 2013 at 2:10 AM, Alexey Vasiliev < leopard_ne(at)inbox(dot)ru > wrote:
>> Воскресенье, 24 ноября 2013, 14:06 +01:00 от Andres Freund
>> < andres(at)anarazel(dot)de >:
>>
>> Hi,
>>
>>
>> On 2013-11-24 16:27:06 +0400, Олексій Васильєв wrote:
>>> This is part where I try to connect to database:
>>> https://github.com/le0pard/pg_web/blob/master/src/pg_web.c#L92-L132 , but
>>> SPI functions give error in log (it is commented):
>>>
>>> 2013-11-24 02:57:43 UTC ERROR: stack depth limit exceeded
>>> 2013-11-24 02:57:43 UTC HINT: Increase the configuration parameter
>>> "max_stack_depth" (currently 2048kB), after ensuring the platform's stack
>>> depth limit is adequate.
>>> 2013-11-24 02:57:43 UTC CONTEXT: SQL statement "SELECT COUNT(*) FROM
>>> pg_class;"
>>>
>>> Because I doing something in wrong way. I will appreciate for any help:
>>> where I doing wrong, link to the article how to do it, just a tip, pull
>>> request - anything. Google search and PostgreSQL sources reading so far
>>> helped me to this point.
>>
>> At the very least you're calling InitPostgres() instead of
>> BackgroundWorkerInitializeConnection() which you have commented out. And
>> the latter should only be called once in every worker.
>>
>> Greetings,
>>
>> Andres Freund
>>
>>
>> Fixed by using PQconnectdb from "libpq-fe.h". Thanks.
>You should not need an extra PQconnectdb to connect to a database
>using a background worker for your case as far as I understood. By
>using that you are requiring a connection to database without using
>the internal infrastructure in place, meaning that your bgworker is
>not connected to the database server from the inside but from the
>outside, like a normal client would do. Aren't to trying to have a
>background worker connected to a database when it is initialized with
>BgWorkerStart_PostmasterStart? Bgworkers using this start-up mode are
>not eligible to initialize database connections. Please use either
>BgWorkerStart_ConsistentState or BgWorkerStart_RecoveryFinished and
>BackgroundWorkerInitializeConnection will allow a connection to
>database without any extra work.
>--
>Michael
Thanks, I just try this. This work if I working with database in loop inside bgw_main function. But if I create threads inside bgw_main and try to connect to database - I have errors "stack depth limit exceeded" . The code:

https://github.com/le0pard/pg_web/blob/master/src/pg_web.c#L195  - connect to database
https://github.com/le0pard/pg_web/blob/master/src/pg_web.c#L100-L131  - "http_event_handler" function execute in threads, because it handle http requests. And this code not work. BTW, I need connect to database depend from request url, so execute BackgroundWorkerInitializeConnection at the beginning not enough.

Thanks again.

--
Alexey Vasiliev