Re: How to know killed by pg_terminate_backend

>> >> Seems reasonable. Does the victim backend currently know why it has been
>> >> killed?
>> >
>> > I don't think so.
>> >
>> > One idea is postmaster sets a flag in the shared memory area
>> > indicating it rceived SIGTERM before forwarding the signal to
>> > backends.
>> >
>> > Backend check the flag and if it's not set, it knows that the signal
>> > has been sent by pg_terminate_backend(), not postmaster.
>> 
>> Or it could also be sent by some other user process, like the user
>> running "kill" from the shell.
> 
> No problem (at least for pgpool-II).
> 
> If the flag is not set, postgres returns the same code as the one
> killed by pg_terminate_backend(). The point is, backend is killed by
> postmaster or not. Because if backend was killed by postmaster,
> pgpool-II should not expect the PostgreSQL server is usable since
> postmaster decided to shutdown.

Here is the patch to implement the feature.

1) pg_terminate_backend() sends SIGUSR1 signal rather than SIGTERM to
   the target backend.
2) The infrastructure used for message passing is
   storage/ipc/procsignal.c The new message type for ProcSignalReason
   is "PROCSIG_TERMNINATE_BACKEND_INTERRUPT"
3) I assign new error code 57P04 which is returned from the backend
   killed by pg_terminate_backend().

#define ERRCODE_TERMINATE_BACKEND			MAKE_SQLSTATE('5','7', 'P','0','4')

Comments are welcome.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
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