Designated historian

More than one historian can write in the same profile, but exactly one of them answers long-range tag and history queries. A second historian is for logging different collections in different historians. Retrieval still uses only one of them. Enable Designated tag historian reader on that one component and leave it disabled on the others. A new TAG Local Historian has this setting on by default so a simple profile can answer history queries with only this checkbox.

flowchart LR
    subgraph Profinity["Profinity"]
        Tags --> Historian["Designated historian"]
    end
    subgraph Store["Database"]
        History["Tag history"]
    end
    Historian --> History
    History --> Queries["History queries"]

Tag history is written by each historian, and long-range history queries are answered from the store of the historian that has Designated tag historian reader enabled

If no component is designated, or more than one is, Profinity has no store to read history from and does not answer long-range queries. In that case, a dashboard shows only the values in memory, and the Live and View at a time control does not appear in its title bar. An InfluxDB historian is designated only while its Allow retrieval setting is also enabled. Allow retrieval exists only on the InfluxDB historians. Designated tag historian reader is described on the page of each historian: TAG Local Historian, InfluxDB historians and TAG SQL Historian.

Dashboards use the designated historian for older values in a chart window, and for viewing a dashboard at a past time, as described in View a dashboard at a past time. To set up logging, refer to How to configure data logging.