ODP.NET Connection Pooling Issues - Fault Tolleran

问题:

I have an WebAPI service using ODP.NET to make connections to several oracle databases. Normally the web service would be hit several times a second and will never have long periods on inactivity. In our test site however, we did not use it for 2-3 days. This morning, we hit the service and got "connection request timeout" exceptions from ODP.NET, suggesting that the connection pool was out of available connections. We are closing the connections after use. The service was working fine before the period, but today the very first query got the timeout exception. Our app pool in IIS is configured to never reset.

My question then is, what can cause the connection pool to fill with bad connections after a period of inactivity, where these connections are not cleaned up in the usual 3 minute cycle? It only happened to 2 out of the 3 of our databases, and Validate Connection=true is set for all of them.

EDIT So after talking to the DBA, there is some different between a connection/session being killed manually or by timeout and the database server severing the TCP connections. In this case, the TCP connection was severed as part of a regular backup (why is not important for this). I guess this happens when the whole database server goes offline at once. The basis of the question still applies I think though: why is ODP.NET unable to cleanup severed connections overtime? There is a performance counter that refers to "Stasis" connections, could those connections be stuck in that state? I would think that it should be able to see that a connection is no longer active (Validate Connection=True), kill it and not return it to the pool.

Granted, this problem can be solved by just resetting the app pool everything the database goes down. I would still like to configure ODP.NET connection pooling to be more fault tolerant.

回答1:

I have run into this same issue, and the only solution I have found is to use the Connection Lifetime connection string parameter in conjunction with Validate Connection.

In my particular case, the connection timeout was set at the server and the connections in the pool would timeout, but not be sniped out of the pool, resulting in errors.

Setting both the Connection Lifetime and the Validate Connection parameters has resolved the issue.

Make sure the Connection Lifetime value that you choose is less than the server connection inactivity timeout.

回答2:

The recommended solution is to use ODP.NET Fast Connection Failover (FCF). FCF will automatically remove invalid connections from the pool such that you don't need to use Validate Connection, Connection Lifetime, nor clear the pool.

To use FCF, set "HA events=true", use connection pooling, and have your DBA set up Fast Application Notification (FAN) on the server side. FAN is what alerts the ODP.NET pool when a DB service or node goes down or rebooted. Upon receiving the message, ODP.NET knows which connections to remove from the pool and removes them, leaving all other valid connections untouched.

回答3:

Something else is going on here. Min Pool Size and some of the other settings help when the connection is severed from things like DBA configured idle timeouts and firewall tcp idle timeouts, 'connection request timeout' occurs when created a new connection.

This could be simple network problem. There could be something interfering with dns resolution of the servers. Another case is not having fully qualified entries in tnsnames. I've been bit by the latter a couple of times.

The other issue is the one you've already recognized - full pool.

Double check that you don't have a connection leak somewhere. A missing .Close is one thing but if you're not using a 'using' statement, a try/finally is required as an unhandled exception could be thrown prior to the .Close.

I would use perfmon to monitor some of the connection statistics to start - NumberOfPooledConnections, NumberOfActiveConnections, etc: