Package bw :: Package poseidon :: Module diskindex :: Class DiskIndex

Class DiskIndex

object --+
         |
        DiskIndex

This is the top-level abstract class which defines the interface for all DiskIndexes in use. DiskIndexes are dictionary-like objects and can be accessed and updated by index assignment. However, they are also transaction based and must be committed to save changes to disk. However, they do *not* support MVCC semantics. Storage objects must be careful to acquire a common lock when doing updates.

Instance Methods

__init__(self, fn, options)
x.__init__(...) initializes x; see x.__class__.__doc__ for signature

__setitem__(self, key, value)
Add a key-value pair.

update(self, d)
Same as dict.update

__getitem__(self, key)
Retrieve the value of a key.

__contains__(self, key)
Returns True if key is in the DiskIndex.

has_key(self, key)
Same as __contains__

get(self, key, failobj=None)
Same as dict.get

__len__(self)
Not implemented.

__iter__(self)

iteritems(self)

commit(self)
Commit the DiskIndex.

clean(self, oldest)
Clean the cache of old-entries.

close(self)
Safely shut down the index.

read_disk(self, key)
Read key from disk.

Inherited from object: __delattr__, __getattribute__, __hash__, __new__, __reduce__, __reduce_ex__, __repr__, __setattr__, __str__

Properties
Inherited from `object`: `__class__`

Method Details

init(self, fn, options)
(Constructor)

x.__init__(...) initializes x; see x.__class__.__doc__ for signature

Parameters:

fn - The fully qualified pathname of the storage. e.g. "/home/username/brainwave/db/mmap". No extension is provided.
options (dict) - A dictionary containing additional options

Overrides: object.__init__

setitem(self, key, value)
(Index assignment operator)

Add a key-value pair. Does not commit.

getitem(self, key)
(Indexing operator)

Retrieve the value of a key.

Reads from an internal read-cache before searching on disk.

contains(self, key)
(In operator)

Returns True if key is in the DiskIndex. Not implemented.

commit(self)

Commit the DiskIndex. Not Implemented

clean(self, oldest)

Clean the cache of old-entries. Should be run asynchronously in a separate thread. Does *not* lock the dictionary before making modifications. This method is the *only* place where cache entries are removed. If the cache is added to while this method is in progress, the clean will silenty fail with a "Dictionary size changed during iteration" error. This is not a problem. The next time, it will work fine. The idea is that this method should never hog CPU from a main worker thread.

close(self)

Safely shut down the index. Not Implemented

read_disk(self, key)

Read key from disk. Not implemented