Hi- How frequently Postgres Poll for trigger file

On 01.12.2010 13:27, aaliya zarrin wrote:

I want to know how frequently postgres search for trigger file to switch
over.

In 9.0, every 100ms while streaming replication is active and connected.
5 seconds otherwise. In current git master branch, it's always 5 s.

Can this switch over time be reduced?

Not without hacking the sources and compiling.

Although, on many platforms, Linux included I believe, sending a signal
to the startup process should wake it up from the sleep and make it
check the trigger file immediately. "pg_ctl reload" for example should
do it. So if �ou send a signal to the startup process immediately after
creating the trigger file, it should take notice sooner.

Plz let me know where postgres poll for trigger file. I could find it out in
"backend/access/trans/xlog.c" ? am i right?

Yes. search for callers of CheckForStandbyTrigger() function.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com

Heikki Linnakangas escreveu:

On 01.12.2010 13:27, aaliya zarrin wrote:

I want to know how frequently postgres search for trigger file to switch
over.

In 9.0, every 100ms while streaming replication is active and connected.
5 seconds otherwise. In current git master branch, it's always 5 s.

Can this switch over time be reduced?

Not without hacking the sources and compiling.

Although, on many platforms, Linux included I believe, sending a signal
to the startup process should wake it up from the sleep and make it
check the trigger file immediately. "pg_ctl reload" for example should
do it. So if �ou send a signal to the startup process immediately after
creating the trigger file, it should take notice sooner.

Isn't it an ugly solution for stopping the replication immediately? At the top
of my head, I don't remember the reason for not turn the interval for pooling
trigger file into a configurable option. IMHO, high availability fits into
those cases (switchover immediately).

[poking the git history a little...]

I agree the a short polling interval is not energy efficient [1]http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=723d0184e2972f21db0f85feef3d35f0cb9b3298 but some
scenarios need this short interval. So if we want to stop the replication
immediately, we have two options: (i) advertise that we need to signal the
postmaster after creating a trigger file or (ii) made the pooling interval
configurable. As you said, there are platforms that a signal doesn't wake up a
process, so I suggest (ii) but I'm fine to include (i) at docs too.

Comments?

[1]: http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=723d0184e2972f21db0f85feef3d35f0cb9b3298
http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=723d0184e2972f21db0f85feef3d35f0cb9b3298

--
Euler Taveira de Oliveira
http://www.timbira.com/

Thanks for quick response..
Can I change this 5 second time?
I have seen the postgres code as well.
What is the functionality of WaitLatch() function. I could not understand
completely.
Plz help..

On Wed, Dec 1, 2010 at 5:53 PM, Heikki Linnakangas <
heikki.linnakangas@enterprisedb.com> wrote:

On 01.12.2010 13:27, aaliya zarrin wrote:

I want to know how frequently postgres search for trigger file to switch
over.

In 9.0, every 100ms while streaming replication is active and connected. 5
seconds otherwise. In current git master branch, it's always 5 s.

Can this switch over time be reduced?

Not without hacking the sources and compiling.

Although, on many platforms, Linux included I believe, sending a signal to
the startup process should wake it up from the sleep and make it check the
trigger file immediately. "pg_ctl reload" for example should do it. So if
ıou send a signal to the startup process immediately after creating the
trigger file, it should take notice sooner.

Plz let me know where postgres poll for trigger file. I could find it out

in
"backend/access/trans/xlog.c" ? am i right?

Yes. search for callers of CheckForStandbyTrigger() function.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com

--
Thanks & Regards,

Aaliya Zarrin
(+91)-9160665888

On 01.12.2010 19:23, aaliya zarrin wrote:

Thanks for quick response..
Can I change this 5 second time?
I have seen the postgres code as well.

You can, if you don't mind changing the sources.

What is the functionality of WaitLatch() function. I could not understand
completely.

The recoveryWakupLatch latch allows the startup process to wake up
immediately when new WAL arrives via streaming replication, without
waiting for the whole five seconds to elapse.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com

Hey!!!!!!!!!1
I am able to change the switch over time.. Thanks alot..
2010/12/2 aaliya zarrin <aaliya.zarrin@gmail.com>

Ok.. Thanks I will try!!!

2010/12/2 Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>

Oh, and there's another value for the case we're polling the archive, not

streaming from master. Search for "5" in XLogPageRead function to catch them
all.

On 02.12.2010 08:21, Heikki Linnakangas wrote:

It's the 5000000L argument in the WaitLatch call. It's expressed in
microseconds.

On 02.12.2010 06:39, aaliya zarrin wrote:

Where this 5 Seconds time is defined in the code ???

On Wed, Dec 1, 2010 at 5:53 PM, Heikki Linnakangas<
heikki.linnakangas@enterprisedb.com> wrote:

On 01.12.2010 13:27, aaliya zarrin wrote:

I want to know how frequently postgres search for trigger file to

switch
over.

In 9.0, every 100ms while streaming replication is active and
connected. 5
seconds otherwise. In current git master branch, it's always 5 s.

Can this switch over time be reduced?

Not without hacking the sources and compiling.

Although, on many platforms, Linux included I believe, sending a
signal to
the startup process should wake it up from the sleep and make it
check the
trigger file immediately. "pg_ctl reload" for example should do it.
So if
ıou send a signal to the startup process immediately after creating the
trigger file, it should take notice sooner.

Plz let me know where postgres poll for trigger file. I could find it
out

in
"backend/access/trans/xlog.c" ? am i right?

Yes. search for callers of CheckForStandbyTrigger() function.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com

--
Thanks & Regards,

Aaliya Zarrin
(+91)-9160665888

--
Thanks & Regards,

Aaliya Zarrin
(+91)-9160665888

On Thu, Dec 2, 2010 at 12:16 AM, Euler Taveira de Oliveira
<euler@timbira.com> wrote:

As you said, there are platforms that a signal doesn't wake up a
process, so I suggest (ii) but I'm fine to include (i) at docs too.

Can we use "pg_ctl kill" to send signal on such platforms?

Regards,

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

On 03.12.2010 03:55, Fujii Masao wrote:

On Thu, Dec 2, 2010 at 12:16 AM, Euler Taveira de Oliveira
<euler@timbira.com> wrote:

As you said, there are platforms that a signal doesn't wake up a
process, so I suggest (ii) but I'm fine to include (i) at docs too.

Can we use "pg_ctl kill" to send signal on such platforms?

It won't make a difference, "pg_ctl kill" sends the signal just like
regular "kill". Except that "pg_ctl kill" also works on Windows which
doesn't have the concept of Unix signals.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com