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From Xinhuan Zheng <xzh...@christianbook.com>
Subject Re: Disconnect database connection after idle timeout
Date Thu, 13 Nov 2014 15:29:27 GMT
We don’t have any front end proxy. We don’t use DBD::Gofer nor PGBouncer. However, we do
use Apache::DBI. The mod_perl application on our servers connect to database when they need
to.  The database connection can be idle for a long time if there is no more requests then
we’ll get TCP/IP timeout. We are seeing a lot of TNS timeout errors in oracle alert trace
log. When that happens, the corresponding httpd process on the other hand is still there.
If a request comes in and happens to use that httpd process (the other side oracle server
process may have timed out already too), the customer would get “not connect to oracle”
error. Other than that, having many idle oracle server processes for a long time is wasting
of system resources like RAM. To address those issues, I would think implementing the idle
TTL is appropriate. The oracle has implemented connection pooling in 11G. I would think this
is to address the issue on their side. If the client implementation is too hard, then I guess
the appropriate solution is to use Oracle 11g connection pooling. I just want to solicit other
people’s opinion how to better address the issue.

- xinhuan

From: John Dunlap <john@lariat.co<mailto:john@lariat.co>>
Date: Thursday, November 13, 2014 at 10:01 AM
To: Perrin Harkins <pharkins@gmail.com<mailto:pharkins@gmail.com>>
Cc: Xinhuan Zheng <xzheng@christianbook.com<mailto:xzheng@christianbook.com>>,
Paul Silevitch <paul@silevitch.com<mailto:paul@silevitch.com>>, modperl <modperl@perl.apache.org<mailto:modperl@perl.apache.org>>
Subject: Re: Disconnect database connection after idle timeout

We use PGBouncer on the web server(which handles keep-alive to the database) and then we use
Apache::DBI across localhost to talk to PGBouncer.

On Thu, Nov 13, 2014 at 9:56 AM, Perrin Harkins <pharkins@gmail.com<mailto:pharkins@gmail.com>>
wrote:
Hi,

Can you explain what problem you're trying to solve? Apache processes don't have the option
of doing things when there is no request to serve, so you can't easily have them disconnect.
It may be possible with alarms or cron jobs or something, but it's probably not a good idea.

If you tune your configuration to avoid leaving large numbers of servers idle, you should
not have problems with unused connections. Also, make sure you are using a front-end proxy
of some kind and not serving static HTTP requests from your mod_perl server.

If your problem is that you need more active connections than your server can handle, you
could look at DBD::Gofer:
http://www.slideshare.net/Tim.Bunce/dbdgofer-200809

- Perrin

On Thu, Nov 13, 2014 at 9:39 AM, Xinhuan Zheng <xzheng@christianbook.com<mailto:xzheng@christianbook.com>>
wrote:
Your understanding is correct. It’s what I am looking for. However, due to the apache forking
child nature, I don’t feel comfortable using SIGALARM.

We use Apache::DBI. I would prefer having enhancement in this module. Currently the module
is implementing apache process wide global cache for db connections, which we already use.
But one missing piece in this module is to handle the TTL (time-to-live) for a cached db connection.
 If TTL were implemented, the module would have to disconnect from db connection after a pre-defined
timeout so the oracle server process could be shut down more gracefully. Would it be possible
to implement that? Or is it too hard to implement?

- xinhuan

From: Paul Silevitch <paul@silevitch.com<mailto:paul@silevitch.com>>
Date: Wednesday, November 12, 2014 at 11:53 PM
To: Xinhuan Zheng <xzheng@christianbook.com<mailto:xzheng@christianbook.com>>,
modperl <modperl@perl.apache.org<mailto:modperl@perl.apache.org>>
Subject: Re: Disconnect database connection after idle timeout

I don't fully understand your need here.  I'm going to give my best.

You could set an alarm in the cleanup handler that calls the disconnect after a specified
amount of time.  If a new request comes in, you could cancel the alarm in a postreadrequest
handler (or something early in the cycle).  To cover the race condition where the disconnect
happens right before the cancel, you could check to make sure the database connection is active
right after the cancel is called.

HTH,

Paul

On Wed, Nov 12, 2014 at 9:36 PM, Xinhuan Zheng <xzheng@christianbook.com<mailto:xzheng@christianbook.com>>
wrote:
Hello,

I am having a database connection management question. Our apache+mod_perl application initiates
a database connection request when it needs to then do data processing. Afterwards, if there
is no more requests coming to this apache process, the database connection basically will
be sitting there in idle state for quite a while until the OS TCP/IP idle timeout has reached.
At that point the database would send a message into its alert log, telling that a connection
timeout has occurred and the server process will be cleaned. I would like to figure out if
mod_perl application can implement keep-alive timeout mechanism. The mod_perl would maintain
the database connection after it finishes some processing until an idle timeout defined in
the application has reached, for example, 5 minutes. Then the mod_perl would initiate a database
disconnection request so the server process can be cleaned more gracefully. We are using Oracle
11g database. I knew in 11G oracle has implemented the connection pooling. I would think the
oracle side connection pooling would be the server side maintaining the connection idle timeout.
Would it be possible on the client side the mod_perl implement something like that? I just
don’t know which side is more appropriate and how on the client side it can implement something
like that.

Thanks,
- xinhuan





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John Dunlap
CTO | Lariat

Direct:
john@lariat.co<mailto:john@lariat.co>

Customer Service:
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support@lariat.co<mailto:support@lariat.co>
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