Load Limiting

Load Limiting

sendmail can queue (and not attempt to deliver) mail if the system load average exceeds a specified maximum. The x option defines this maximum limit. When the load average exceeds the maximum, sendmail tests each message's priority by using the following algorithm, where q is the value associated with the q option, and x is the value associated with the x option:

q / (load_average - x + 1)

In IRIX sendmail, the algorithm is modified slightly. The number of child processes forked by the sendmail daemon is added to the load average. Thus, a host with a load average of 1 but with 6 forked sendmail processes has an effective load average of 7.

After the final load average is calculated, sendmail compares it to the message priority for each message. If the priority is greater, sendmail sets the delivery mode to q (queue only).

The default value for the q option is 10000; each point of load average is worth 10000 priority points. The X option defines the load average at which sendmail refuses to accept network connections. Locally generated mail (including incoming UUCP mail) is still accepted.