Tango Database#
The Tango Database, also referred to as TangoDB, is a service mainly used for name lookup and static and runtime configuration storage for the control system. The Tango Database itself is found by clients and servers via the environment variable TANGO_HOST. It is possible to run multiple databases for load-balancing and fault-tolerance, see Use multiple database servers within a Tango control system, and also to run servers without database, see Run a device server without a database.
The part of the Tango Database that offers an API is implemented as a device server and should always be running. It is abbreviated as TDB in the following paragraphs.
Name lookup#
When a device server starts it registers itself with the TDB. For this to work the device name has to be added to the TDB before with tools like Jive or tango_admin. This is called device exporting/unexporting, see the RFC for the details. The device server unregisters itself automatically on shutdown from the TDB.
The device registration allows to abstract-away the location of the device server. So when the device server moves from hostA to hostB this is completely invisible to the client.
Alias handling#
It is possible to introduce alternative names for devices and attributes and this mapping is also stored in the TDB. See Alias names for an in-depth explanation and the howto for some examples on how to use them.
Configuration storage#
The TDB can also act as a key-value store for storing persistent device server data. The keys are called properties in Tango and the values are strings. As the properties an be read by anyone, no sensitive data should be stored in them.
The previous values of properties are also kept in the database for informative purposes. The default depth of the history is 10 and can be controlled with the historyDepth device property. The history is deleted when a property is deleted.