There are three very useful data points that are missing from the default access_log LogFormat: the Process/Thread ID and time taken to process request. Those are the %P (PID), %{tid}P (TID), and %T (time taken).

We frequently have to request customers to enable these flags, restart httpd, and reproduce issues related to long-running requests. The time taken obviously helpful. The PID/TID are helpful to correlate requests with pstack output.