Historical data sets are collections of online history tag sets that are currently accessible to history client applications. There are three classifications of historical data sets:
An active historical data set holds the most recent historical data captured for all history tags configured for this historian. It holds the contiguous historical data record from the time it was started until the present.
The content of an active historical data set grows as it accumulates history tags and history samples from the real-time data stream from the data capture system.
To assist in data management, the DeltaV Continuous Historian can be configured to automatically roll over the active historical data set. The active historical data set is closed and becomes a current historical data set. A new, empty active historical data set is started. The configuration rules for performing a rollover can be based on:
A new active historical data set can also be created directly using the Create New Active Data Set tool in the Continuous Historian Administration application.
Current historical data sets are created by active historical data set rollover operations. They hold historical data for a collection of history tags within the time span of the data set. They provide a means to manipulate historical data captured in manageable chunks, while keeping as much of the recently captured data accessible to history client applications as possible.
For the current historical data sets, you can configure the following on the Advanced tab of the Continuous Historian Properties dialog:
If automatic export has been configured, once the Primary storage size limit has been reached, the DeltaV Continuous Historian will perform an export of the oldest data set and remove it from Primary storage.
You can manually export data from and/or discard current historical data sets using the Continuous Historian Administration application.
Extended historical data sets provide a means to bring back online historical data that has been exported and no longer online; that is, made re-accessible to history client applications.
The Continuous Historian Administration application allows you to create extended historical data sets from historical data files. Once created, historical data in the extended historical data set is accessible in the same way as the data in the active and current historical data sets. There are no assumptions about continuity of the data in an extended historical data set with any of the other data online. The history tags in the extended historical data set need not match, nor are they constrained by, the other history tags available online.
The DeltaV Continuous Historian performs no automatic data management for extended historical data sets. They remain online and occupy storage until you manually remove them.