Re: JDBC keep alive issue

On Fri, Aug 10, 2012 at 7:19 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Haifeng Liu <liuhaifeng(at)live(dot)com> writes:
> > I have a program running like a daemon, which analyze data and write to
> postgresql 9.1 on centos 5.8. There is only one connection between my
> program and the postgresql database, and I hope the connection may keep
> alive all the time. But I failed, the connection will be reset after idle
> for about 2 hours.
>
> > jdbc driver: 9.1-901, connection url has parameter tcpKeepAlive=true;
> > postgresql:9.1, keep alive related settings use default
> values(commented);
> > centos 5.8 64bit, net.ipv4.tcp_keepalive_intvl = 75, probes = 9, time =
> 7200.
>
> IIRC, time = 7200 (seconds) means to start sending keepalive packets
> after 2 hours of idle time. So if you have something in the way that is
> dropping the connection after 2 hours, these settings will not activate
> keepalive soon enough to save it. I'd try setting that to 3600.
>

I use a much shorter time (300). Why not? The keepalive pings are a
trivial amount of data. I've found over the years that router NAT tables
are a big offender (probably doesn't apply in this case) ... some drop your
internal-to-external IP address mapping after as little as five minutes.

Craig

>
> > There is no firewall or any other device which behaves force idle
> connection cleanup.
>
> Seems pretty darn unlikely given these symptoms. Look harder...
> maybe something you thought was just a bridge has got routing behavior.
>
> BTW, in the real world connections drop for all sorts of reasons, and
> kernel keepalive configurations can't prevent them all. You might be
> better advised to build some reconnect-after-connection-loss logic into
> your application, rather than spending time on making this work.
>
> regards, tom lane
>
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