Let’s combine all of what we’ve learned about how to effectively use CouchDB from Clojure to implement an asynchronous work queue based on the events being emitted into the logging database we considered earlier. First, a refresher on what that data looks like:

{:evt-type "auth/new-user" :username "Chas"}
{:evt-type "auth/new-user" :username "Dave"}
{:evt-type "sales/purchase" :username "Chas" :products ["widget1"]}
{:evt-type "sales/purchase" :username "Robin" :products ["widget14"]}
{:evt-type "sales/RFQ" :username "Robin" :budget 20000}

Now, you could add a single watch for changes in the logging database, and instead of echoing those events to *out*, do something useful with them; that’s a perfectly valid thing to do, especially if your requirements are relatively simple. However, most real-world systems need some additional levers to pull to control event processing loads and more ably support modular design requirements.