Indexing is the process by which the set of documents is analyzed and the data entered into the database. Recoll indexing is normally incremental: documents will only be processed if they have been modified. On the first execution, of course, all documents will need processing. A full index build can be forced later on by specifying an option to the indexing command (recollindex -z).
Recoll indexing takes place at discrete times. There is currently no interface to real time file modification monitors. The typical usage is to have a nightly indexing run programmed into your cron file.
Recoll knows about quite a few different document types. The parameters for document types recognition and processing are set in configuration files Most file types, like HTML or word processing files, only hold one document. Some file types, like mail folder files can hold many individually indexed documents.
Recoll indexing processes plain text, HTML, openoffice and e-mail files internally. Other types (ie: postscript, pdf, ms-word, rtf) need external applications for preprocessing. The list is in the installation section.
Without further configuration, Recoll will index all appropriate files from your home directory, with a reasonable set of defaults.
In some cases, it may be interesting to index different areas of the file system to separate databases. You can do this by using multiple configuration directories, each indexing a file system area to a specific database. You would use the RECOLL_CONFDIR environment variable or the -c confdir option to recollindex to indicate which configuration to process. The recoll search program can use any selection of the existing databases for each search, this is configurable inside the user interface.