``appendonly`` README
=====================
This package provides a set of data structures for use in ZODB applications
where standard BTrees are poor fits for an application's requirements.
In particular, these data structures are designed to minimize conflict
errors when doing frequent "append" operations to queues and stacks.
``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
``appendonly.Accumulator``
--------------------------
This class provides a list-like data structure, where the only mutations
allowed are to append to or clear the list. Intended uses are for a
set of pending operations / changes / notifications, which get processed
as a unit (at which point the accumulator is cleared).
``appendonly`` Changelog
========================
1.2 (2014-12-28)
----------------
- Add support for Python 3.4.
- Make ``ZODB`` dependency unconditional, now that it fully supports Py3k.
- Add support for testing on Travis.
1.1 (2013-11-28)
----------------
- Add ``Accumulator.extend`` method to enhance list-ness.
- Add support for PyPy.
- Add support for Python 3.2 / 3.3.
1.0.1 (2013-02-25)
------------------
- Fix brown-bag in 1.0 release (``Accumulator.append`` changes were not
persisted).
1.0 (2013-02-25)
----------------
- Add a conflict-free 'Accumulator' class: manages a queue of items which
can be iterated, appended to, or conumed entirely (no partial / pop).
- Automate tests for supported Python versions via 'tox'.
- Drop support for Python 2.4 / 2.5.
0.10 (2012-02-21)
------------------
- Add 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.
