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From: Magnus Hagander on 9 Feb 2010 08:45
On Tue, Feb 9, 2010 at 14:03, Tollef Fog Heen
<tollef.fog.heen(a)collabora.co.uk> wrote:
>
> (please Cc me on replies, I am not subscribed)
>
> Hi,
>
> libpq currently does not use TCP keepalives.  This is a problem in our
> case where we have some clients waiting for notifies and then the
> connection is dropped on the server side.  The client never gets the FIN
> and thinks the connection is up.  The attached patch unconditionally
> adds keepalives.  I chose unconditionally as this is what the server
> does.  We didn't need the ability to tune the timeouts, but that could
> be added with reasonable ease.

Seems reasonable to add this. Are there any scenarios where this can
cause trouble, that would be fixed by having the ability to select
non-standard behavior?
I don't recall ever changing away from the standard behavior in any of
my deployments, but that might be platform dependent?

If not, I think this is small and trivial enough not to have to push
back for 9.1 ;)

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Me: http://www.hagander.net/
Work: http://www.redpill-linpro.com/

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From: Tollef Fog Heen on 9 Feb 2010 08:57
]] Magnus Hagander

| Seems reasonable to add this. Are there any scenarios where this can
| cause trouble, that would be fixed by having the ability to select
| non-standard behavior?

Well, it might be unwanted if you're on a pay-per-bit connection such as
3G, but in this case, it just makes the problem a bit worse than the
server keepalive already makes it – it doesn't introduce a new problem.

| I don't recall ever changing away from the standard behavior in any of
| my deployments, but that might be platform dependent?

If you were (ab)using postgres as an IPC mechanism, I could see it being
useful, but not in the normal case.

| If not, I think this is small and trivial enough not to have to push
| back for 9.1 ;)

\o/

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Tollef Fog Heen
UNIX is user friendly, it's just picky about who its friends are

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From: Andrew Chernow on 9 Feb 2010 09:34
Tollef Fog Heen wrote:
> (please Cc me on replies, I am not subscribed)
>
> Hi,
>
> libpq currently does not use TCP keepalives. This is a problem in our
> case where we have some clients waiting for notifies and then the
> connection is dropped on the server side. The client never gets the FIN
> and thinks the connection is up. The attached patch unconditionally
> adds keepalives. I chose unconditionally as this is what the server
> does. We didn't need the ability to tune the timeouts, but that could
> be added with reasonable ease.

ISTM that the default behavior should be keep alives disabled, as it is
now, and those wanting it can just set it in their apps:

setsockopt(PQsocket(conn), SOL_SOCKET, SO_KEEPALIVE, ...)

If you really want libpq to manage this, I think you need to expose the
probe interval and timeouts. There should be some platform checks as
well. Check out...

http://www.mail-archive.com/pgsql-hackers(a)postgresql.org/msg128603.html

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Andrew Chernow
eSilo, LLC
every bit counts
http://www.esilo.com/

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From: Fujii Masao on 9 Feb 2010 20:07
On Tue, Feb 9, 2010 at 11:34 PM, Andrew Chernow <ac(a)esilo.com> wrote:
> If you really want libpq to manage this, I think you need to expose the
> probe interval and timeouts.

Agreed.

Previously I was making the patch that exposes them as conninfo
options so that the standby can detect a network outage ASAP in SR.
I attached that WIP patch as a reference. Hope this helps.

Regards,

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Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center
From: daveg on 10 Feb 2010 16:08
On Tue, Feb 09, 2010 at 09:34:10AM -0500, Andrew Chernow wrote:
> Tollef Fog Heen wrote:
> >(please Cc me on replies, I am not subscribed)
> >
> >Hi,
> >
> >libpq currently does not use TCP keepalives. This is a problem in our
> >case where we have some clients waiting for notifies and then the
> >connection is dropped on the server side. The client never gets the FIN
> >and thinks the connection is up. The attached patch unconditionally
> >adds keepalives. I chose unconditionally as this is what the server
> >does. We didn't need the ability to tune the timeouts, but that could
> >be added with reasonable ease.
>
> ISTM that the default behavior should be keep alives disabled, as it is
> now, and those wanting it can just set it in their apps:
>
> setsockopt(PQsocket(conn), SOL_SOCKET, SO_KEEPALIVE, ...)

I disagree. I have clients who have problems with leftover client connections
due to server host failures. They do not write apps in C. For a non-default
change to be effective we would need to have all the client drivers, eg JDBC,
psycopg, DBD-DBI, and the apps like psql make changes to turn it on. Adding
this option as a non-default will not really help.

-dg


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David Gould daveg(a)sonic.net 510 536 1443 510 282 0869
If simplicity worked, the world would be overrun with insects.

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