Historian

The Historian is MACHHUB’s time-series store. Live tag values are transient — they exist only while a subscriber is listening. The Historian keeps a durable, queryable record of how a tag’s value changed over time.

Historizing a tag

Any tag can be historized by turning on its Historize setting (you do this in the Unified Namespace). Each historized tag chooses a type, a sampling time, and a retention period:

Type	Behavior
On change (event)	A point is written every time the value changes. Best for state, setpoints, and discrete signals.
Time series (timeseries)	The value is recorded on a fixed cadence given by the sampling time. Best for continuous analog signals.

The retention period controls how long points are kept; a background job periodically removes points older than the retention window.

flowchart LR
  Tag["Tag value changes"]
  Tag -- "On change" --> OnChange["Write a point on each change"]
  Tag -- "Time series" --> Sampled["Write a point every sampling interval"]
  OnChange --> Store[("Historian")]
  Sampled --> Store
  Store -- "retention period" --> Cleanup["Old points pruned"]

Querying history

MACHHUB stores each historized point as a timestamp/value pair, ordered by time. You read history two ways:

• In the console — the Historian view lets you browse historized tags, chart them over a time range, and export to CSV. See Console Historian.
• From your app — the SDK Historian fetches points for a tag over a time range, so apps can render their own charts.

MACHHUB also supports time-bucketed aggregation — grouping points into intervals (for example, one-minute buckets over a one-hour range) — so charts stay responsive over long ranges and large datasets.

flowchart TB
  Hist[("Historian")]
  Hist --> Raw["Raw points\n(time, value)"]
  Hist --> Agg["Aggregated buckets"]
  Hist --> CSV["CSV export"]
  Raw --> Chart["Charts & dashboards"]
  Agg --> Chart

Continue with Upstreams to relay tags to another MACHHUB instance, or revisit the Unified Namespace to enable historization on a tag.