Shutting down server from a backend process, e.g. walrceiver

On Tue, Sep 21, 2010 at 9:48 AM, fazool mein <fazoolmein@gmail.com> wrote:

Hi,

I want to shut down the server under certain conditions that can be checked
inside a backend process. For instance, while running symmetric replication,
if the primary dies, I want the the walreceiver to detect that and shutdown
the standby. The reason for shutdown is that I want to execute some other
stuff before I start the standby as a primary. Creating a trigger file
doesn't help as it converts the standby into primary at run time.

Using proc_exit() inside walreceiver only terminates the walreceiver
process, which postgres starts again. The other way I see is using
ereport(PANIC, ...). Is there some other way to shutdown the main server
from within a backend process?

Are you going to change the source code? If yes, you might be able to
do that by making walreceiver send the shutdown signal to postmaster.

If no, I think that a straightforward approach is to use a clusterware
like pacemaker. That is, you need to make a clusterware periodically
check the master and cause the standby to end when detecting the crash
of the master.

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center

On Mon, Sep 20, 2010 at 05:48:40PM -0700, fazool mein wrote:

Hi,

I want to shut down the server under certain conditions that can be
checked inside a backend process. For instance, while running
symmetric

Synchronous?

replication, if the primary dies, I want the the walreceiver to
detect that and shutdown the standby. The reason for shutdown is
that I want to execute some other stuff before I start the standby
as a primary. Creating a trigger file doesn't help as it converts
the standby into primary at run time.

Using proc_exit() inside walreceiver only terminates the walreceiver
process, which postgres starts again. The other way I see is using
ereport(PANIC, ...). Is there some other way to shutdown the main
server from within a backend process?

Perhaps I've misunderstood, but since there's already Something
Else(TM) which takes actions, why not send a message to it so it can
take appropriate action on the node, starting with shutting it down?

Cheers,
David.
--
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Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter
Skype: davidfetter XMPP: david.fetter@gmail.com
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On Mon, Sep 20, 2010 at 9:44 PM, Fujii Masao <masao.fujii@gmail.com> wrote:

On Tue, Sep 21, 2010 at 9:48 AM, fazool mein <fazoolmein@gmail.com> wrote:

Hi,

I want to shut down the server under certain conditions that can be

checked

inside a backend process. For instance, while running symmetric

replication,

if the primary dies, I want the the walreceiver to detect that and

shutdown

the standby. The reason for shutdown is that I want to execute some other
stuff before I start the standby as a primary. Creating a trigger file
doesn't help as it converts the standby into primary at run time.

Using proc_exit() inside walreceiver only terminates the walreceiver
process, which postgres starts again. The other way I see is using
ereport(PANIC, ...). Is there some other way to shutdown the main server
from within a backend process?

Are you going to change the source code? If yes, you might be able to
do that by making walreceiver send the shutdown signal to postmaster.

Yes, I'll be modifying the code. In the walreceiver, I used the following to
send a shutdown to the postmaster:

kill(getppid(), SIGTERM);

If no, I think that a straightforward approach is to use a clusterware
like pacemaker. That is, you need to make a clusterware periodically
check the master and cause the standby to end when detecting the crash
of the master.

This was another option, but I have to modify the code for this particular
case.

Thanks for your help.

Regards,

On Tue, Sep 21, 2010 at 8:32 AM, David Fetter <david@fetter.org> wrote:

On Mon, Sep 20, 2010 at 05:48:40PM -0700, fazool mein wrote:

Hi,

I want to shut down the server under certain conditions that can be
checked inside a backend process. For instance, while running
symmetric

Synchronous?

I meant streaming :), but the question is in general for any process forked
by the postmaster.

replication, if the primary dies, I want the the walreceiver to
detect that and shutdown the standby. The reason for shutdown is
that I want to execute some other stuff before I start the standby
as a primary. Creating a trigger file doesn't help as it converts
the standby into primary at run time.

Using proc_exit() inside walreceiver only terminates the walreceiver
process, which postgres starts again. The other way I see is using
ereport(PANIC, ...). Is there some other way to shutdown the main
server from within a backend process?

Perhaps I've misunderstood, but since there's already Something
Else(TM) which takes actions, why not send a message to it so it can
take appropriate action on the node, starting with shutting it down?

(wondering)

Thanks.

On Wed, Sep 22, 2010 at 2:50 AM, fazool mein <fazoolmein@gmail.com> wrote:

Yes, I'll be modifying the code. In the walreceiver, I used the following to
send a shutdown to the postmaster:

kill(getppid(), SIGTERM);

You can use the global variable "PostmasterPid" instead of getppid.
There are three types of shutdown. SIGTERM triggers smart shutdown.
Smart shutdown is suitable for your case? If not, you might need to
send SIGINT or SIGQUIT instead.

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center

Thanks for the tips.

In our case, SIGINT makes more sense. I'll use that.

Regards

On Tue, Sep 21, 2010 at 7:50 PM, Fujii Masao <masao.fujii@gmail.com> wrote: