HADR stands for high availability disaster recovery .This solution is used for disaster recovery purpose on db2 udb databases.HADR should be configured properly inorder to have optimal performance:
1)HADR synchronization mode:HADR can be run in 3 different modes SYNC,NEARSYNC,ASYNC.SYNC mode gives the best protection to data.In this mode primary has to wait until the changes are committed and written on the standby.Primary waits for the acknowledgement from the standby server.In NEARSYNC mode, standby sends acknowledgement as soon as the logs are in memory of standby server.And in ASYNC mode , primary does not wait for any kind of acknowledgement from the standby.Proper synchronization mode has to be chosen for optimal performance
2)DB2_HADR_BUF_SIZE:This registry variable controls the size of the receive buffer .Receive buffer is the area of memory where the logs are received before they are replayed.You can use the db2pd -db dbname -hadr on standby to monitor the usage of receive buffer.If you see it reaching 100 during the workload, you need to increase the value of DB2_HADR_BUF_SIZE
3)DB2_HADR_SOSNDBUF and DB2_HADR_SORCVBUF:There are the socket send buffer size and socket receive buffer size respectively.If the size for these parameters is too small then the full bandwidth can not be utilized.Generally increasing this to a bigger value would not impact performance negatively.
4)Logfilsz:Size of the logfile plays an important role in the performance,Generally this size should be few hundred MB.