If running many concurrent units of execution is an important aspect of your product, consider adding a concurrency view. It can show what issues and bottlenecks you may have (unless that sounds too detailed). Other good reasons to include it are the reliance on interprocess communication, having a non-straightforward task structure, concurrent state management, synchronization, or task failure handling logic.
Use whatever notation you want for this view, as long as it captures the units of execution and their communication. Assign priorities to your processes and threads, if necessary, and then analyze any potential issues, such as deadlocks or contention. You can use state diagrams to show the possible states and their transitions for important units of execution (waiting for queries, executing a query, distributing results, and so on).
If you're not sure about the need to introduce concurrency to your system, a good rule of thumb is don't. And if you must...
