Full retrieval

In Full retrieval mode, all stored data points are returned, regardless of whether a value or quality has changed since the last value. This mode enables the same value and quality pair (or NULL value) to be returned consecutively with their actual timestamps. It works with all types of tags.

By using Full retrieval in conjunction with storage without filtering (that is, no delta or cyclic storage mode is applied at the historian), you can retrieve all values that originated from the plant floor data source or from another application.

Full retrieval best represents the process measurements recorded by the Historian. However, it imposes a higher load on the server, the network, and the client system because a very large number of records may be returned for longer time periods.

The following illustration shows how values are returned for Full retrieval:

Data is retrieved in full mode with a start time of T1 and an end time of T2. Each dot in the graphic represents an actual data point stored on the historian. From these points, the following are returned:

• P2, because there is no actual data point at T1

• P3 through P12, because they represent stored data points during the time period