appendonly 0.10

appendonly.AppendStack

This class provides a LIFO stack of separately-persisted objects:

• The stack manages a set of “layer” objects, with a configurable limit on the number of layers. Each layer has a configurable maximum length, and a sequential generation number.

• The stack appends items to most recent layer until the layer is filled; it then adds a new layer.

• If the number of layers then exceeds the configured maximum, the stack pruneds the oldest layer(s) to conform to that limit.

• When pruning, the stack calls an application-supplied callback for archiving / cleanup of the pruned layer.

• Iteration over the stack yields (generation, index, object) tuples. in reverse order to that in which the objects were appended.

The stack is implemented as a single persistent record, with custom ZODB conflict resolution code.

appendonly.Archive

This class provides a linked list of separately-persisted copies of layer data pruned from an AppendStack. The intended use would be something like:

from appendonly import AppendStack from appendonly import Archive

class RecentItems(object):

def __init__(self):

self._recent = AppendStack() self._archive = Archive()

def pushItem(object):

self._stack.push(object, self._archive.addLayer)

def __iter__(self):

for generation, index, item in self._stack:

yield item

for generation, index, item in self._archive:

yield items

0.10 (2012-02-21)

• Added an ‘Archive’ class, intended to support long-term storage of the layer data pruned from an ‘AppendStack’.

0.9 (2010-08-09)

• Initial public release.