Netsplit detection is enabled by default (to disable it, use M-x customize-variable RET erc-modules).
When an IRC server becomes disconnected from the others in a network, a netsplit has occurred. At this time it’s possible that many users appear to leave all at once. This can easily fill channel windows with quit messages when the split happens and join messages when the servers are connected again.
ErcNetsplit detects such splits and does not show the quit messages caused by them. It keeps track of who left during the split, which you can see by using the command /WHOLEFT or its alias /WL. ErcNetsplit registers a netjoin once somebody who left in the split has returned. If all users returned, the netjoin is considered complete, and the information from this netsplit will be removed.
After 10 minutes, the information from an old netsplit is removed from memory, since it’s possible that users who split may have quit or parted the channel during the netsplit, and their new joins would be ignored otherwise.
Two hooks are provided with this module: