Usage

Use rack.set*.PersistentSet as you would use a set, and rack.dict*.PersistentDict as you would use a dict, except that:

• On construction:

  • They need to take a name argument indicating the (prefix to the) location of the underlying LMDB database.

  • For LMDB, they can take a hash argument if you want to specify a non-default hasher (default is SHA256).

  • They can take a serdes argument which you can use to specify a non-default serializer/deserializer (default is Python’s marshal).

• On use:

  • They must be used with a context manager, which is required in order to properly manage the lifetime of the database open/close, as __init__ / __del__ would not be sufficient due to the garbage collected nature of Python.

  • Operations that create a new container (eg. union, copy), take an optional name parameter, which allows to specify the location of the new database.

If you know you store elements of limited size (less than LMDB max key size), you can use rack.set_small.PersistentSet, which is ~2x faster than the non-small one due to one less indirection. If keys are too big, lmdb.BadValsizeError exceptions will occur.