CLUSTERS
The server availability index is approximately equal to the percentage of the total server capacity that is still available. For example, if the server availability index is 65, you still have approximately 65% of the capacity of your server available. Although the servers in your enterprise may vary in power and resources, the server availability index represents the same thing on each server -- the amount of total availability of that server that is still available.
The server availability index is based on the expansion factor, which is determined by comparing recent response times for specific types of transactions to the minimum time in which the server has ever completed the same types of transactions. For example, if the server is currently averaging 12 microseconds to perform Database Open transactions but the minimum time the server has ever performed a Database Open transaction is 3 microseconds, the expansion factor for Database Open transactions would be 4 (the current time of 12 microseconds divided by the fastest time of 3 microseconds). In other words, the expansion factor determines how many times longer it takes for a transaction to complete currently than it takes under optimal conditions.
Domino stores the minimum time for each type of transaction in memory and in the LOADMON.NCF file, which the server reads each time it starts. When the server shuts down, Domino updates the LOADMON.NCF file with the latest information.
To determine the current expansion factor, Domino tracks the most commonly used types of Domino transactions for specified periods of time. By default Domino tracks these transactions for 5 periods of 15 seconds each. Domino then determines the average time it took to complete each type of transaction and divides that time by the minimum time it ever took to complete that same type of transaction. This determines an expansion factor for each type of transaction. To determine the expansion factor for the entire server, Domino averages the expansion factors for all the types of transactions, giving a heavier weighting to the most frequently used types of transactions.
As the server gets busier, adding more load has an increasingly greater effect on performance and availability. Thus, adding more load to a busy server increases the expansion factor faster than adding more load to a less busy server.
An expansion factor of 64 is considered the maximum load for a server. In other words, if the server is taking 64 times longer to complete transactions than it does under optimal conditions, Domino considers the server to be fully loaded.
How the availability index compares to the expansion factor To determine the availability index, Domino uses a formula that converts the expansion factor into an approximation of the percentage of the total server capacity that is still available. The following table shows a few examples of expansion factors converted to availability indexes.
Changing the amount of data used to compute the expansion factor Although it is not usually necessary, you can use the following NOTES.INI settings to change the amount of data that Domino collects in order to figure the expansion factor.