External indexers configuration

The index data and the access method are linked by the rclbes (recoll backend storage) Doc field. You should set this to a short string value identifying your indexer (e.g. the filesystem indexer uses either FS or an empty value, the Web history indexer uses BGL, the Joplin notes indexer uses JOPLIN).

The link is actually performed inside a backends configuration file (stored in the configuration directory). This defines commands to execute to access data from the specified indexer. Example, for the mbox indexing sample found in the Recoll source (which sets rclbes="MBOX"):

fetch = /path/to/recoll/src/python/samples/rclmbox.py fetch
makesig = /path/to/recoll/src/python/samples/rclmbox.py makesig
index = /path/to/recoll/src/python/samples/rclmbox.py index

When updating the index, the recollindex will execute the value of the the index parameter, if present (it may not be present if this concerns an external index).

If an external indexer needs to store additional configuration parameters, e.g. path to a specific instance of the indexed application, etc., I suggest storing them inside recoll.conf, with a backend-specific prefix (e.g. joplin_db, mbox_directory) and using methods from the rclconfig module to access them.