sendmail, 4th Edition

Persistent Queue Runners with -qp

V8.12 sendmail introduced persistent queue runners as a solution to some of the problems caused by periodic queue runners. Periodic queue runners are the result of a normal -qinterval command-line switch, or a Runners= queue-group equate. Either causes:

• sendmail to fork one or more queue runners to process a queue or queue group each interval

• Every queue runner to open and read all the files in the queue to gather a list of envelopes to deliver

Persistent queue runners avoid these problems because a single process is dedicated to a queue, a queue group, or a grouping of queue groups (called a “workgroup”). A persistent queue runner is launched just like the periodic command-line queue runner, but with the addition of a p character:

-qpinterval

The p causes one or more persistent queue runners to be launched, one per queue group. One will be launched to handle your default queue group, and one more will be launched to handle each queue group defined by a QUEUE_GROUP mc option. Depending on the number of queue directories in each, these can be combined into a single workgroup. When you have many queue groups, you can end up with multiple workgroups controlling persistent runners.

Each persistent queue runner will sleep for interval. When it awakes, it reads all the files in the queues that belong to its workgroup, and sorts all the envelopes it finds into the proper order needed for delivery. After it has finished ordering the envelopes, it launches one ...