[pgpool-hackers: 1101] Re: pgpool-II 3.4 problems

[Muhammad Usama]

Hi Ishii San

I think this difference of behavior between 3.3. And 3.4 is caused by the
commit "cb735f22441001b6afdbb5bac72808db66094ca9" that was not ported to
the 3.4 branch.

http://git.postgresql.org/gitweb/?p=pgpool2.git;a=commit;h=cb735f22441001b6afdbb5bac72808db66094ca9

Thanks
Best regards
Muhammad Usama



On Tue, Oct 13, 2015 at 2:45 PM, Tatsuo Ishii <ishii at postgresql.org> wrote:

> > Usama,
> >
> > While I have been working on:
> > http://www.pgpool.net/mantisbt/view.php?id=147
>
> Oops. This is wrong. Here is the correct one.
>
> http://www.pgpool.net/mantisbt/view.php?id=145
>
> > I found there was an interesting behavior change between pgpool-II 3.3
> > and 3.4.
> >
> > It turns out that the bug was related to the action when
> > client_idle_limit is reached. In 3.3, when client_idle_limit is
> > reached, following statement is executed (pool_process_query.c):
> >
> > if (idle_count > pool_config->client_idle_limit)
> > {
> >       pool_log("pool_process_query: child connection forced to terminate
> due to client_idle_limit (%d) reached,
> >                pool_config->client_idle_limit);
> >               pool_send_error_message(frontend, MAJOR(backend),
> >               "57000", "connection terminated due to client idle limit
> reached",
> >                                       "","",  __FILE__, __LINE__);
> >       return POOL_END_WITH_FRONTEND_ERROR;
> > }
> >
> > then goes to this (child.c)
> >
> > if (status == POOL_END_WITH_FRONTEND_ERROR ||
> >    pool_config->connection_cache == 0 ||
> >    !strcmp(sp->database, "template0") ||
> >    !strcmp(sp->database, "template1") ||
> >    !strcmp(sp->database, "postgres") ||
> >    !strcmp(sp->database, "regression"))
> > {
> >       reset_connection();
> >       pool_close(frontend);
> >       pool_send_frontend_exits(backend);
> >       pool_discard_cp(sp->user, sp->database, sp->major);
> > }
> >
> > This results in closing connection to backend.
> >
> > In 3.4,
> >
> > if (idle_count > pool_config->client_idle_limit)
> > {
> >       ereport(ERROR,
> >            (pool_error_code("57000"),
> >                errmsg("unable to read data"),
> >                  errdetail("child connection forced to terminate due to
> client_idle_limit:%d is reached",
> >                   pool_config->client_idle_limit)));
> > }
> >
> > Then jump to backend_cleanup() and call pool_process_query() to
> > execute queries defined in reset_query_list. This results in sending
> > typically "DISCARD ALL" to backend. The problem reported in the bug id
> > 147 happens in this route (actually the reporter claims that pgpool-II
> > hangs in sending "DISCARD").
> >
> > In summary, when client idle limit reaches, pgpool-II 3.3 disconnects
> > connections to backend, while 3.4 does not close the connections to
> > backend and sends DISCARD to backend.
> >
> > We have a few reports that pgpool-II 3.4 hangs while sending DISCARD
> > and I wonder those problems somewhat related to the behavior change
> > described above because the code path in 3.4 is executed even if
> > client_idle_limit is not reached (elog(ERROR...)).
> >
> > Usama,
> >
> > Was this behavior change intentional?
> >
> > Best regards,
> > --
> > Tatsuo Ishii
> > SRA OSS, Inc. Japan
> > English: http://www.sraoss.co.jp/index_en.php
> > Japanese:http://www.sraoss.co.jp
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