History blocks and partitions

AVEVA Historian stores data in history blocks. History blocks use a proprietary file format and are essentially subfolders of the main historian storage folder.

Although the tag values are stored in history blocks on disk, the values appear to be saved to tables in the Runtime database.

Each history block stores all data for a specified duration. The default history block duration is one day, but may be as little as one hour. When there is data to be stored in that time interval, Historian creates a new history block for that data. For example, if a history block is defined for a day's worth of data, when it receives the first data value for the second day, Historian creates a new one-day history block and places the corresponding data into the new block.

As data is acquired, the size of these history blocks grows on a continual basis, being limited only by the size of the hard disk on which the historian resides.

If the historian was not running for some time, or if a history block is deleted, for a certain time period, there may be a gap in the sequence of history blocks -- also known as a block gap.

History block formats are specially optimized for storing time-series data, while general-purpose database management systems typically are not.

Compact storage formats reduce the storage space requirements than would be required in a general-purpose database. Upon retrieval, historical data is presented by the AVEVA Historian OLE DB provider as if it were stored in SQL Server tables.

Historian partitions

Historian organizes history blocks within partitions. As real-time data arrives, Historian stores it in history blocks located in the main data partition. At the same time, Historian automatically computes and records a corresponding hourly summary for each analog tag value received. The auto-summary values are stored in auto-summary history blocks within the auto-summary partition.

For more information on history blocks and partitions, see Manage partitions and history blocks in the AVEVA Historian Administration Guide.