Save and restore AtomSpace contents to a RocksDB database. The RocksDB database is a single-user, local-host-only file-backed database. That means that only one AtomSpace can connect to it at any given moment.
In ASCII-art:
+-------------+
| AtomSpace |
| |
+---- API-----+
| |
| RocksDB |
| files |
+-------------+
RocksDB is a "real" database, and so datasets too big to fit into RAM can be stored in it. This back-end does not try to guess what your working set is; it is up to you to load, work with and save those Atoms that are important for you. The goal of the examples is to show exactly how to do this. These are:
- fetch-store.scm -- Basic fetch and store of single atoms
- load-dump.scm -- Loading and saving entire AtomSpaces.
The next demo is more curious. It allows queries to be run so that only a specific portion of the database is loaded into the AtomSpace. The query will run correctly, in that it will behave as if the entire AtomSpace had been loaded into RAM. However, it does not actually require that everything be loaded; Atoms are fectched from the filestore in an as-needed basis. This is currently a bit experimental; the API is subject to change without notice (and there may be bugs?)
- query-storage.scm -- Run queries out of the database.
All AtomSpace backends are encapsulated with StorageNodes, and can
thus be treated as ordinary Atoms. Among other things, this allows
multiple databases to be simultaneously opened for reading and writing.
- multiple-databases.scm -- Several at once.
AtomSpaces can be stacked, one on top another. Each space in the stack is called a "frame", and it holds a change-set: all of the Atoms and Values that changed from the spaces further down in the stack. This stack (actually, a DAG) can be stored and fetched, just as above.
- space-frames.scm -- A stack of AtomSpace Frames.