Historian and trend

Write path

Runtime → local JSONL spool → ready/ → (optional) historian-writer or embedded VION_HISTORIAN_DIR columnar flush.

Query

http

GET /api/v1/tags/{id}/history?from=&to=&limit=

[from,to) RFC3339
limit 1–500
Downsample: downsample or aggregate = avg|min|max, optional bucketMs
Command token not required
PG + not-yet-flushed spool are merged

Studio Historian surface: from/to/limit + downsample + SVG trend + sample table.

HMI sparkline: limit=60.

Retention

VION_HISTORIAN_RETENTION_DAYS / _SECS (writer side).

WARNING

There is no HA failover for the historian. In multi-tenant setups, use a separate DB/directory per process.