Solace has recently released version 8.3.0 of the Solace Appliance and in it we’ve added support for topic subscription exceptions. Using topic subscription exceptions allows you to easily exclude specific topics from the set of topics delivered to a queue by adding a leading “!” to the topic subscription.
Let’s walk through an example of how this works. Consider an order management system in which a group of servers divides up orders alphabetically based on symbol. In other words, one server subscribes to ORDERS/A*, while another subscribes to ORDERS/B* and so on.
This distribution of symbols to order processors is based on the average trading day. For example, let’s say there is particularly hot IPO with ticker symbol SLCE. On a normal day trading is pretty quiet in equities with symbols starting with “S”, but on this day trading volume is expected to be very high (because of the SLCE IPO). It’s a lot of work to rebalance the load on the order processors for a single day, especially considering the problem is caused by trading in one symbol. This is where the subscription exception comes in.
Support for topic subscription exceptions allows you to effortlessly handle this scenario using our standard topic syntax. In other words, you can configure the regular server to subscribe to ORDERS/S* and !ORDERS/SLCE, while you configure a dedicated server to subscribe to ORDERS/SLCE. Any messages published to ORDERS/SLCE are dropped by the regular server and accepted by the dedicated server.
When the day is over, you can simply remove the dedicated server and the !ORDERS/SOL topic subscription exception on the regular server to return everything to its original configuration.