Effects of configuration changes on the system

Different types of dynamic changes to the database affect the system in different ways.

A summary of typical changes and their effect on the system after a commit is as follows.

• Modifying system parameters
  A modification to system parameters usually takes effect immediately. If you change the HistoryCacheSize parameter and commit the change, the cache is not immediately flushed to bring the cache size to less than or equal to the new value.

• Modifying storage locations
  Modifying the circular storage location requires a shutdown and restart of AVEVA Historian. Changes to the other storage locations take effect immediately.

• Adding, deleting, and modifying tags
  Modifying data acquisition characteristics of a tag could result in a brief period of data loss, for that tag. As a guideline, any change to the source of data for the tag (for example, modifying the item name, topic name, or I/O server name of the tag) will result in a short gap in data for the tag, while the system disconnects from the old data source and connects to the new data source.

• Adding, deleting, and modifying IDASs
  Adding a new IDAS to the system results in a new set of system tags being added (the status and performance system tags associated with that IDAS).

  Modifying an IDAS may result in data loss for the tags serviced by that IDAS (for example, moving an IDAS to another computer causes a disconnect from the data sources).

• Adding, deleting, and modifying I/O Servers and topics
  Modifying I/O Server or topic characteristics may result in data loss for their tags, if the modification implies a disconnect from the data source.