Summary: Connection Request Timeout Messages.
Applies to: Subversion MultiSite, CVS MultiSite - All versions

Sometimes in the WANdisco logs, connection request timeout information message will be logged. This is an informational message and should be ignored unless it is guaranteed that the connection can be established in xxx milli-seconds and happens often. 

In normal operation of WANdisco, there are two connections established between each of the replicated machines, a DConE connection and a DFTP connection. These two connections were established when the WANdisco application started and were used when required. A keep-alive signal is sent on DConE connection periodically. There is no traffic on DFTP until a file transfer.

Some buggy routers in the path of the two end points will close an established connection if there is no traffic on the connection without notifying the end points. When end points sent data on this stale connection, they hung forever. To deal with these buggy routers, WANdisco does not keep the DFTP open in its connection pool forever. WANdisco application established a DFTP connection from receiver to sender when a transfer of a file was required. This solved the problem dealing with buggy routers.

Some companies have a corporate policy that the network connections can only be established in one direction. To deal with this scenario, the replicated machines will establish a DFTP connection to other nodes periodically and tear them down if there is no traffic within a known interval. Once a connection is established, any side is free to use the connection regardless which side initiated the connection. A connection in use will never be torn down until it is available as free connection. This is the current implementation.

It takes between 300 to 400 milli-seconds to establish a network connection even on a slow Wide Area Network (WAN). By default, WANdisco waited for 500 milli-seconds before giving up that a connection cannot be established to a peer machine and prints this informational message. What if the establishments of connection always take 501 milli-seconds. In this case, a connection will never be established. To solve this problem, the timeout value is adjusted in 10% increment of the last timeout starting at 500 milli-seconds to a maximum of 10 second for each timed out connection. Upon establishment of a successful connection, this timeout value is used for subsequent connection establishment unless an adjustment is required for failed attempts.

Last edit: mlucas 2nd Oct 2009