Archiving

audience:all lang:all

The Archiving of Tango Controls allows one to store Attribute values.

The current recommendation for archiving of Attribute values is to use the Historical Data Base++ or HDB++. HDB++ supports high time resolution, multiple database backends (MySQL, Timescale, SQLite), and is based on Tango Attribute events. The improvements over its now deprecated predecessor HDB are higher throughput and a number of improvements behind the curtain, among them better error handling and smaller demand for resources (RAM and CPU).

There is also SNAP. It is not a real archiver in the way that HDB++ works, but it allows to take snapshots of sets of attributes at the same time[1]. One can think of it as a camera that can only take photos of one moment in time but not videos. HDB++ on the other hand could be configured to act almost like a video recorder if one had unlimited resources (RAM, CPU, storage space).

• HDB++
  • An overview
  • Elements
    • Backend support
    • Configuration Manager Device Server
    • Event Subscriber Device Server (Archiver)
    • HdbConfigurator Server
    • HdbViewer
  • Source code
  • Documentation for building and installing
  • Rationale
  • Presentations and papers
• SNAP

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[1]

Same time is not really possible because a distributed control system will always introduce delays somewhere. What we refer to here is a best effort: The computer that takes the snapshot will read the values of all attribute as fast as possible. It is possible that a device does not reply immediately when one of its attributes is read. This will result in a delay that one will notice when looking at the timestamps of the attributes in the snapshot.