Determining the number of users currently using a system is difficult, particularly if the log does not contain events for both the beginning and 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.
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 has expired for each transaction. Let's start with our ...