If there an entry of some IP with MAC resolution X, and this entry is updated to MAC resolution Y, then ArpNotificationHandler sleeps for 2s.

From mailing list:

• ArpNotificationHandler is sleeping for 2s each time it gets an ARP request/reply which changes a resolved MAC address in the cache.
  Even though this scenario sounds rare, current ext-gw resolve implementation creates packets that cause that all the time, and therefore we hit this code block quite a lot.

We see two sleeps introduced in the entire ArpNotificationHandler and they are applicable only when there is a MAC migration seen for an existing IP address.. By MAC migration, means the ODL controller is receiving that same IP in packets now from a different interface.

The sleeps are introduced because when a MAC migration happens for an existing IP, there is a VRF Entry refresh lifecycle that gets triggered for that IP.

In order to make sure VRF removal is completely processed for old interface, before we do a VRF add for the same IP Address for the new interface a sleep was added between the removal and add operations..