CLUSTERS

How workload balancing works
By distributing databases throughout the cluster, you balance the workload in the cluster so that no server is overloaded. In addition, there are several NOTES.INI variables you can set to help balance the workload. For example, you can specify a limit on how busy a server can get by specifying an availability threshold. When the server reaches the availability threshold, the Cluster Manager marks the server BUSY. When a server is BUSY, requests to open databases are sent to other servers that contain replicas of the requested databases. You can also specify the maximum number of users you want to access a server. When the server reaches this limit, users are redirected to another server. This keeps the workload balanced and keeps the server working at optimum performance.

When a user tries to open a database on a BUSY server, the Cluster Manager looks in the Cluster Database Directory for a replica of that database. It then checks the availability of the servers that contain a replica and redirects the user to the most available server. If no other cluster server contains a replica or if all cluster servers are BUSY, the original database opens, even though the server is BUSY.

Example
This example describes how IBM® Lotus® Domino™ performs workload balancing. This cluster contains three servers. Server 2 is currently BUSY because the workload has reached the availability threshold that the administrator set for this server. The Cluster Managers on Server 1 and Server 3 are aware that Server 2 is BUSY.

Workload balancing in a cluster

1. An IBM® Lotus® Notes® user attempts to open a database on Server 2.

2. Domino sends Notes a message that the server is BUSY.

3. Notes looks in its cluster cache to find the names of the other servers in the cluster.

4. Notes accesses the Cluster Manager on the next server listed in the cluster cache.

5. The Cluster Manager looks in the Cluster Database Directory to find which servers in the cluster contain a replica of the desired database.

6. The Cluster Manager looks in its server cluster cache to find the availability of each server that contains a replica.

7. The Cluster Manager creates a list of the servers in the cluster that contain a replica of the database, sorts the list in order of availability, and sends the list to Notes.

8. Notes opens the replica on the first server in the list (the most available server). If that server is no longer available, Notes opens the replica on the next server in the list.