SQL*Net message from client (SNMFC) is a fascinating and misunderstood wait event. Simply stated, Oracle server processes post this event when they are waiting for a message from their client process so they can do some work. Oracle server processes are either consuming CPU or waiting for something. When a server process has nothing to do, it posts the SNMFC wait event.

This wait event can be posted because a user is taking a coffee break, resulting in both an idle client and server process. It could also be posted because the user is thinking about what to do next, again causing both the client and server process to be idle. A server process could also be posting this event because a network problem is preventing it from receiving a message the client process has already sent. And finally, the server process could post the event because the Oracle client process is doing some advanced processing that is taking a while to complete. In each of these cases, the SNMFC wait event is posted by the server process. So our challenge is to understand if we care!

When looking at all sessions together as a single unit of work, known as profiling the system, while some SNMFC wait events may be the result of a network or client processing issue, the vast majority of the SNMFC postings will be from both an idle client and server processes patiently waiting for something to do. This is why most wait event reports filter out this wait event. In fact, because most Oracle sessions spend more time waiting than doing work, if the SNMFC wait time were included in the typical wait event report, it would effectively dwarf all the other wait time we dearly care about and desperately need for our analysis.