Selecting an environment backend

The MacroServer persists the macro environment in a database. The storage backend is selected with the EnvironmentDb attribute. In case Sardana is used with Tango this configuration is accessible via the EnvironmentDb MacroServer device property. Three backends are available: shelve (default), Redis and Tango DB.

The backend is chosen based on the format of the EnvironmentDb value:

`EnvironmentDb` value	Backend
`<file system path>`	shelve (default)
`redis://...` / `rediss://`	Redis
`property` / `property:...`	Tango DB (free object properties)

The MacroServer needs to be restarted in order to apply a change of the EnvironmentDb property.

Shelve backend (default)

By default the environment is stored in a file using the Python shelve module. The EnvironmentDb value is interpreted as the path of this file, by default: /tmp/tango-<user>/<ds_exec_name>/<ds_inst_name>/macroserver.properties. The path may contain the %(ds_exec_name)s, %(ds_inst_name)s and %(ds_name)s substitution patterns. The parent directory is created automatically if it does not exist.

Warning

Many systems clean the /tmp directory on reboot. If you want your environment to survive reboots, configure the EnvironmentDb property to point to a persistent location, e.g.:

import tango
db = tango.Database()
db.put_device_property(
    "macroserver/demo1/1",
    {"EnvironmentDb": "/var/lib/sardana/demo1/macroserver.properties"})

The underlying dbm implementation used by shelve can be selected with the MS_ENV_SHELVE_BACKEND custom setting:

None (default) - first try gnu and if not available fall back to dumb
"gnu" - better performance, but requires an additional package, e.g. python3-gdbm on Debian
"dumb" - worst performance but directly available with Python 3

Note

If the MacroServer cannot store/retrieve the environment from the configured path at startup, it sets up a new unique temporary path, stores it permanently in the EnvironmentDb property and uses it from then on. Check the server logs if your environment unexpectedly appears empty.

Redis backend

To store the environment in a Redis database, set the EnvironmentDb property to a Redis URI, e.g.:

redis://localhost:6379/0

Both redis:// and rediss:// (TLS) URIs are supported. The keys are prefixed with the MacroServer name, so multiple MacroServers may share the same Redis database. This backend requires the redis Python package (redis-py) to be installed.

Note

If the Redis server cannot be reached at startup, the MacroServer aborts its initialization (it does not fall back to another backend).

Tango DB backend

To store the environment as free object properties in the Tango database, set the EnvironmentDb property to:

property

In this case the properties are stored under the object named after the MacroServer. Alternatively you can choose the object name explicitly:

property:<object name>

This backend does not require any extra service nor package - the environment lives in the same Tango DB as the rest of your configuration and is backed up together with it.