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The underlying message transport of HAManager is a reliable publish/subscribe messaging service, known as Distribution and Consistency Services (DCS). A buffer is created to hold unprocessed incoming messages and outgoing messages that have not been acknowledged. The default memory size is 10MB with the rationale to reduce memory footprint. As the buffer is shared with DRS for HTTP session replication and stateful session bean state replication, you might want to increase the buffer size if your WebSphere environment has high replication demands.
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Important: The replication function was heavily tuned for the 6.0.2 release of WebSphere, and we recommend at least that level to customers with heavy HTTP session replication needs. |
When an appserver is running low on the transport buffer, various messages are displayed in the SystemOut.log of the JVM as shown in Example 6-4.
Example 6-4 Congestion related messages in SystemOut.log
#### Messages indicating congestion ####
DCSV1051=DCSV1051W: DCS Stack {0} at Member {1}: Raised a high severity congestion event for outgoing messages. Internal details are {2}.
...
DCSV1052=DCSV1052W: DCS Stack {0} at Member {1}: Raised a medium severity congestion event for outgoing messages. Internal details are {2}.
DCSV
...
#### Message indicating that congestion cleared ####
DCSV1053=DCSV1053I: DCS Stack {0} at Member {1}: Outgoing messages congestion state is back to normal.
These are not error messages. They are simply informational messages that indicate a congestion event has occurred in the transport buffer. The messages that are not sent during the congestion are retried later, or they are sent as a batch to use the transport buffer more efficiently.
Congestion should normally only occur when doing a lot of session replication or when a large core group is started by simultaneously starting all members. Congestion can be reduced by tuning the buffer size.
