Determining concurrency

Determining the number of users currently using a system is difficult, particularly if the log does not contain events for both the beginning and the end of a transaction. With web server logs in particular, it is not quite possible to know when a user has left a site. Let's investigate a couple of strategies for answering this question.

Using transaction with concurrency

If the question you are trying to answer is how many transactions were happening at a time, you can use transaction to combine related events and calculate the duration of each transaction. We will then use the concurrency command to increase a counter when the events start and decrease when the time for each transaction ...