640px-Brick_WallUnless you run a busy website, Apache‘s MaxClients setting probably isn’t something you think about very often. If not, then look in your Apache 2.2 config and you’ll find a block like this1

    StartServers              5
    MinSpareServers          10
    MaxSpareServers          30
    MaxClients              150
    MaxRequestsPerChild   10000

This setting, along with ServerLimit, controls the number of simultaneous connections that Apache can handle. Above this limit, connections are queued until slots become free. Apache will tell you about this with a message in its error log that looks like—

[Sun Dec 21 01:35:59 2014] [error] server reached MaxClients setting, consider raising the MaxClients setting