Performance considerations

For a complete Historian system, the following components put a demand on memory:

• Internal Historian subsystems, such as the Configuration Manager, data acquisition, and data storage

• The associated Microsoft SQL Server

• The operating system

• Client access (data retrieval), which includes caching

When determining the amount of memory to purchase, remember that adding more memory is the cheapest and easiest thing that you can do to improve performance. Increasing the amount of memory reduces the amount the server has to use virtual memory, thus lowering the load on the storage subsystem. Even if you have a large amount of memory, additional memory is used as additional disk cache, speeding up disk access and therefore file service. Also, processes needed by the server become faster because they are memory-resident.

A major factor in system performance is the amount of plant data you anticipate storing in the system, including considerations about how often that data is stored and retrieved. In general, the more you store, the more often you store it, and the more you retrieve it, the slower the system. The major storage factors affecting the performance of the system are:

• Effective analog flow rate (analog updates per second).

• Period of online data storage required.

• Effective discrete variable flow rate.

• Number of concurrent end users required.

• Complexity of end user queries.

• Number and size of string tags, as well as the effective flow rate of string values.

• Number and duration of string tag retrieval queries, as well as the frequency at which these queries are executed.

A performance report for different historian systems is provided in System sizing examples.