Unless 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