Annotations in PI SMT

Use annotations to associate arbitrary information, such as text comments and other binary data, with a PI archive value.

Use the PI Annotations Editor in the PI SMT Archive Editor to view, edit, insert, and delete annotations to PI point values. Annotations can include comments, notes, supplementary values with specified data types, and files.

Every value in the snapshot or the archive may be annotated. Annotated events always bypass compression. An annotation can be of any binary data type. The size of an annotation is controlled by the Snapshot_AnnotationSizeLimit tuning parameter.

Each archive file has a single associated annotation file, with an .ann extension. The annotation file is created if it does not exist. It is important to store archive and annotation files together, especially when a backed up archive file is restored.

Note: Any operation on an annotation translates into an actual I/O, bypassing archive caching. Annotated events are less efficient than non-annotated events.

You can use the following modes to maintain annotations.

• Standard/Default mode

  Provides a table format that can include alternate values with assigned data types. Use this mode for annotation data that is structured, read programmatically, or exported for use by another application.

  

• String/VARIANT mode

  Stores annotation data as an unspecified VARIANT data type. Use this mode for simple string annotations, annotations that do not require structured data, and to conform with legacy annotations from earlier versions of Data Archive.