Server loading
- Last UpdatedJan 16, 2025
- 2 minute read
When a user connects to the Historian with a client, configuration information is immediately requested from the Historian. This information includes the tags that the server stores, their descriptions, engineering units, and other tag data. SQL Server reads this information from the database (stored on disk) and places it in memory.
As the user selects time periods to trend, the Historian reads data from files located on the disk and prepares the results of the client's data request to be transmitted back to the client. The ability of the server to quickly handle subsequent requests for data from the same client and others is dependent on the server's ability to keep as much information in memory without having to again access data from the disk.
As a higher load is placed for memory, a higher load is placed on the disk I/O system as the server has to use disk caching and read from the data files.
The following table summarizes the loading for various systems.
|
System |
Load Description |
|---|---|
|
Acquisition and storage |
Base load of the Historian. This load exists as long as the system is running. However, this load is not affected by client activity. |
|
Retrieval |
Variable loading caused by data retrieval from client applications. When the client initially connects, the data requested is configuration data, which is stored in SQL Server. The Historian requests data from SQL Server, causing its loading to increase. As the client requests historical data, the disk time increases as information from the data files is transferred to memory. This continues as the client requests additional data. If the client application requests data that has already been transferred to memory, there is no associated disk activity and transfer of data to memory. |
The server must be able to adequately handle the variation on loading caused by the client applications. To accomplish this, make sure that your hardware is sized so that it can handle the base load created by the acquisition and storage systems and that there are adequate resources still available for the retrieval system.