[pgpool-hackers: 1451] Re: Item #11, torward pgpool-II 3.6

[Tatsuo Ishii]

> On Mon, 22 Feb 2016 16:02:03 +0900 (JST)
> Tatsuo Ishii <ishii at postgresql.org> wrote:
> 
>> > Do you mean if we can distiguish TCP connection failure from othres, we
>> > can eliminate unnecessary proces exiting on failover? 
>> 
>> No. I am talking about a problem caused by a cable is pulled out. See
>> the attached mails in the upthread email.
> 
> I'm sorry. I had read the attached mails but I wrote it incorrectly.
> What I want to ask is; when a failover occurs, if we know this isn't caused
> by a cable pllued out, can we handle this without killing the processes?

Yes, if we knew the failure is not caused by a pulled out cable, we
would not need to restart child process.

>> > For example, don't we need to exit processes in the following cases?
>> > 
>> > a. when using pcp_degenerate_node commend
>> 
>> What is pcp_degenerate_node commend?
> 
> It's a mistake. I meant pcp_detach_node. This command is used to
> degenerate the backend manually, and in this case, the failover
> isn't caused by a cable plugged out.
> 
>> 
>> > b. when the backend send ADMIN_SHUTDOWN_ERROR_CODE ("57P01") or
>> >    CRASH_SHUTDOWN_ERROR_CODE "57P02"
>> 
>> Not related to the topic I'm arguing.
> 
> When these error/notice messages are sent, a failover occurs by calling
> notice_backend_error(). However, this is caused administrative shutdown
> of backend and not a cable un-plugged. I think we don't need kill
> processes in this case.
> 
> 
> (pool_process_query.c)
> 4521                 /*
> 4522                  * admin shutdown postmaster or postmaster goes down
> 4523                  */
> 4524                 r = detect_postmaster_down_error(CONNECTION(backend, i), MAJOR(backend));
> 4525                 if (r == SPECIFIED_ERROR)
> 4526                 {
> 4527                     ereport(LOG,
> 4528                         (errmsg("reading and processing packets"),
> 4529                              errdetail("postmaster on DB node %d was shutdown by administrative command", i)));
> 4530                     /* detach backend node. */
> 4531                     was_error = 1;
> 4532                     if (!VALID_BACKEND(i))
> 4533                         break;
> 4534                     notice_backend_error(i);
> 4535                     sleep(5);
> 4536                     break;
> 4537                 }
> 
> 
>> 
>> > c. when we can confirm that there are no problem on TCP connection
>> >    from ping result
>> > 
>> > Of course, this is the exception when the backend is used by the current session.
>> 
>> Yes.
>> 
>> Best regards,
>> --
>> Tatsuo Ishii
>> SRA OSS, Inc. Japan
>> English: http://www.sraoss.co.jp/index_en.php
>> Japanese:http://www.sraoss.co.jp
> 
> 
> -- 
> Yugo Nagata <nagata at sraoss.co.jp>