How do I keep Advantage Database connections from timing out?

Question

I have a Windows Service that works with an advantage database and occasionally makes some http calls. On rare occasions these calls can be very long. To the tune that my database connection times out. I'm not using a Data Module or anything. Just creating the connection manually.

My primary question is what usually prevents the connection from timing out if I just haven't used it in a while? Do the TAdsComponents send a keep alive message that gets called in the background somehow? Is that dependent on the vcl so I don't have that in my service? Somehow I feel like creating a thread to make my http call, and in the main thread checking for it to finish every few seconds would prevent the connection from dying. Is that ever true?

Answer 1

Yes, there is a keepalive mechanism as you expect. The client (for all communication types, TCP, UDP, Shared memory) sends a "ping" to the server every so often to let the server know that connection is still alive. The frequency of that keepalive ping is based on the server configuration parameter CLIENT_TIMEOUT. With the default settings, I believe the keepalive ping is sent every 30 seconds.

The keepalive logic runs in a separate thread that is started by the code that handles the communication. In other words, it does not depend on any of the VCL components; if you have a connection to the server, then that thread should be running.

One way to check if your connections are timing out is to look in the Advantage error log. There should be 7020 errors corresponding to timed out connections.

Some things that come to mind that might result in timed out connections include:

• The client process being suspended for some reason so that the keepalive thread could not run. This seems unlikely.
• The keepalive thread was killed for some reason. This also seems unlikely; you would have to go out of your way to make this happen.
• A firewall may close the connection if there is no activity for a time. I would think, though, that a 30 second interval would be sufficient to prevent that.
• A firewall may disallow the UDP keepalive packets. Firewalls, by nature, are "suspicious" of UDP packets. You might make sure you are using TCP/IP.