> What is the difference between these two, if any? Seems to me they both > accomplish the same thing (allowing one side of a channel to see that the > network is down and thus being able to go Inactive). The only thing I can > guess is that Keep Alive applies only to TCP while Heartbeat will work for > other transmission protocols as well as TCP.
Keepalive and channel Heartbeats do tend to serve similar functions (and actually work in a similar way), but there are some differences between them. Both work by periodically sending data over an otherwise inactive channel. The difference is that Keepalive is performed by TCP/IP 'under the covers' as out-of-band data which MQ is never aware of, and Heartbeats are sent as actual data flows. As you pointed out, this does mean that Keepalive is only available for TCP/IP based channels. Of the two, Keepalive is usually more reliable at detecting network problems since it is always active, even if a channel is in a state where Heartbeats may not normally be sent, such as at the end of a batch of messages when a sender is waiting for confirmation of receipt from the partner. Heartbeats, however, offer some advantages which Keepalive cannot. They will allow the receiver MCA to periodically wake up and see if it has been told to stop mode(quiesce). It also gives an otherwise inactive receiver the opportunity to free any resources it's not used in some time (close target queues, free buffers, etc.). One problem with Keepalive, is that on most platforms, it's only possible to configure one Keepalive interval for ALL TCP/IP connections on the system. This means that if you wanted, say, a 5 minute timeout for your channels, you will inherit the same timeout for every TCP/IP connection one that system which uses Keepalive (e.g. telnet, ftp, etc.). The lower timeout causes extra network traffic as it needs to send additional keepalive packets for each connection which has not seen any activity for the duration of the keepalive timer. The default Keepalive timer on most systems is two hours. In recent times, it's become possible to specify Keepalive times for individual connections on z/OS. On this platform, we now have (in V5.3.0) the KAINT channel attribute, which allows you to specify an individual keepalive timer for any given channel. If you opt to use both Heartbeats and Keepalive, then it's most logical to ensure your Keepalive timer is longer than the HBINT for a channel, otherwise an inactive channel will be sending both Heartbeats and Keepalive packets. Neil Johnston. WebSphere MQ for z/OS Development. Instructions for managing your mailing list subscription are provided in the Listserv General Users Guide available at http://www.lsoft.com Archive: http://vm.akh-wien.ac.at/MQSeries.archive
