[pgpool-general: 9391] Re: WARNING: failed to lock semaphore

[Maria Nieva]

Dear Tatsuo,

Thank you for the clarification.

Regarding the patch, can we apply the same patch to version 4.1.1 of Pgpool
as well?

Best Regards,
Maria






On Fri, Mar 7, 2025 at 6:20 PM Tatsuo Ishii <ishii at postgresql.org> wrote:

> Hi Maria,
>
> > Thank you for the instructions. I have applied the patch.
> >
> > Could you please clarify where I can find log entries that would indicate
> > if `IpcSemaphoreKill` is called? Would I be able to find this information
> > in the pgpool logs?
>
> Yes, in the pgpool log. You should see below if IpcSemaphoreKill is
> called.
>
> +       elog(LOG, "remove semaphore set %lu", semId);
>
> For your information, elog() is a function to log the specified string
> to pgpool log. The first argument is an expected level to be logged.
> It is compared with log_ming_message parameter of pgpool. In the
> default setting, "LOG" will be expected to be emitted if the code is
> executed. The second and the third argument are like arguments of
> printf.
>
> Best reagards,
> --
> Tatsuo Ishii
> SRA OSS K.K.
> English:
> https://protect2.fireeye.com/v1/url?k=31323334-501d2dca-3131568e-454455534531-bbb96eab86ee7dab&q=1&e=4c6cb105-78aa-4ec9-b598-4a1b9e08a728&u=http%3A%2F%2Fwww.sraoss.co.jp%2Findex_en%2F
> Japanese:http://www.sraoss.co.jp
>
> > Best Regards,
> > Maria
> >
> >
> > On Mon, Mar 3, 2025 at 7:26 PM Tatsuo Ishii <ishii at postgresql.org>
> wrote:
> >
> >> Hi Maria,
> >>
> >> Sure.
> >>
> >> Assuming you have the patch at /tmp/log_semaphore_removal.patch
> >> and you have the source at /somewhere/pgpool-II-4.4.6:
> >>
> >> cd /somewhere/pgpool-II-4.4.6
> >> patch -p1 < ~/log_semaphore_removal.patch
> >>
> >> then you can compile and install pgpool as usual.
> >>
> >> Let me know if you have further questions.
> >>
> >> Best reagards,
> >> --
> >> Tatsuo Ishii
> >> SRA OSS K.K.
> >> English:
> >>
> https://protect2.fireeye.com/v1/url?k=31323334-501cfaeb-3131568e-454455535732-b2e8c335807c32bc&q=1&e=6e191e27-bfb2-4c07-873b-af81e2a9270c&u=http%3A%2F%2Fwww.sraoss.co.jp%2Findex_en%2F
> >> Japanese:http://www.sraoss.co.jp
> >>
> >> > Dear Tatsuo,
> >> >
> >> > Thank you for the patch.
> >> >
> >> > I apologize for the inconvenience, but could you please provide
> guidance
> >> on
> >> > how to apply the patch to our Pgpool installation? As mentioned
> >> previously,
> >> > we installed Pgpool from source.
> >> >
> >> > Thank you for your time and assistance.
> >> >
> >> > Best Regards,
> >> > Maria
> >> >
> >> >
> >> >
> >> > On Sat, Mar 1, 2025 at 6:12 AM Tatsuo Ishii <ishii at postgresql.org>
> >> wrote:
> >> >
> >> >> Hi Maria,
> >> >>
> >> >> > Dear Tatsuo,
> >> >> >
> >> >> > Thank you for your response.
> >> >> >
> >> >> > I understand your point regarding the semaphore acquisition.
> However,
> >> I
> >> >> > would like to clarify that the semaphore error does not occur
> >> immediately
> >> >> > after startup. In our experience, the error manifests itself after
> >> weeks
> >> >> of
> >> >> > running Pgpool. This behavior has been observed in both our staging
> >> and
> >> >> > production environments.
> >> >> >
> >> >> > If the semaphore configuration is established during Pgpool
> startup,
> >> it
> >> >> > seems unusual that it would change weeks later. Could you please
> >> >> elaborate
> >> >> > on what might cause such a delayed configuration change?
> >> >>
> >> >> Ok, the semaphore is definitely created at the start up of pgpool. It
> >> >> should never been removed until pgpool shuts down. If it's removed,
> >> >> that must be a bug of pgpool. There's only 1 place where semaphore is
> >> >> removed (IpcSemaphoreKill). Can you apply attached patch to confirm
> >> >> the function is actually called? If you find semaphore is removed but
> >> >> IpcSemaphoreKill is not called, then the semaphore was removed by
> >> >> someone else.
> >> >>
> >> >> Best reagards,
> >> >> --
> >> >> Tatsuo Ishii
> >> >> SRA OSS K.K.
> >> >> English:
> >> >>
> >>
> https://protect2.fireeye.com/v1/url?k=31323334-501cfaeb-3131568e-454455535732-b2e8c335807c32bc&q=1&e=af34ac69-01a0-4305-af59-968a7ca1f337&u=http%3A%2F%2Fwww.sraoss.co.jp%2Findex_en%2F
> >> >> Japanese:http://www.sraoss.co.jp
> >> >>
> >> >>
> >>
>
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