[ZOOKEEPER-417] stray message problem when changing servers

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Fix Version/s: 3.2.0
• Assignee: Benjamin Reed
• Reporter: Benjamin Reed
• Created: 26/May/09 18:10
• Updated: 08/Jul/09 20:24
• Resolved: 26/Jun/09 21:09

Description

There is a possibility for stray messages from a previous connection to violate ordering and generally cause problems. Here is a scenario: we have a client, C, two followers, F1 and F2, and a leader, L. The client is connected to F1, which is a slow follower. C sends setData("/a", "1") to F1 and then loses the connection, so C reconnects to F2 and sends setData("/a", "2"). it is possible, if F1 is slow enough and the setData("/a", "1") got onto the network before the connection break, for F1 to forward the setData("/a", "1") to L after F2 forwards setData("/a", "2").

to fix this, the leader should keep track of which follower last registered a session for a client and drop any requests from followers for clients for whom they do not have a registration.