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CHANGES | ||
======= | ||
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0.6 (unreleased) | ||
---------------- | ||
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- Add support for Python 3.5 till 3.8. | ||
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- Drop support for Python 3.3 and 3.4. | ||
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- Fix a long-standing bug in loadBefore´. The bug was revealed by | ||
testing against ZODB 5, for which loadBefore plays a bigger role. | ||
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0.5.1 (2013-10-25) | ||
------------------ | ||
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- Fix broken release | ||
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0.5.0 (2013-10-25) | ||
------------------ | ||
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Added ZODB4 and Python 3 support. | ||
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0.4.0 (2010-12-09) | ||
------------------ | ||
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Added a "before-from-file" option that can be used if the application wants to | ||
preserve beforestorage state between application restarts. | ||
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0.3.2 (2008-12-05) | ||
------------------ | ||
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Updated to work with both ZODB 3.8 and 3.9. | ||
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0.3.1 (2008-12-01) | ||
------------------ | ||
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Renamed lastTid to getTid to conform to the ZEO.interfaces.IServeable | ||
interface. | ||
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0.3.0 (2008-12-01) | ||
------------------ | ||
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Added Blob support. | ||
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0.2.0 (2008-03-05) | ||
------------------ | ||
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Added support for "now" and "startup" values to the before option when | ||
using ZConfig. The "now" value indicates that the before storage should | ||
provide a view of the base storage as of the time the storage is created. | ||
The "startup" value indicates that the before storage should provide a | ||
view of the base stoage as of process startup time. The later is | ||
especially useful when setting up more than once before storage in a | ||
single application, as it allows you to arrange that all of the | ||
storages provide consistent views without having to specify a time. | ||
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0.1.1 (2008-02-07) | ||
------------------ | ||
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Fixed a packaging bug that caused some files to be omitted. | ||
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0.1 (2008-01-??) | ||
---------------- | ||
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Initial release. |
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See src/zc/beforestorage/README.txt | ||
============== | ||
Before Storage | ||
============== | ||
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ZODB storages typically store multiple object revisions to support | ||
features such as multi-version concurrency control and undo. In the | ||
case of the mod popular storage implementation, old revisions aren't | ||
discarded until a pack. This feature has often been exploited to | ||
perform time travel, allowing one to look at a database as it existed | ||
in at some point in time. In the past, this has been possible with | ||
file storage by specifying a time at which to open the file | ||
storage. This works fairly well, but is very slow for large databases | ||
because existing index files can't easily be used. Time travel is | ||
also supported for individual objects through the ZODB history | ||
mechanism. | ||
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The introduction of multi-version concurrency control provided new | ||
opertunities for time travel. Using the storage loadBefore method, | ||
one can load transaction records written before a given time. ZODB | ||
3.9 will provide an option to the database open method for opening | ||
connections as of a point in time. | ||
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Demo storage can be quite useful for testing, and especially staging | ||
applications. In a common configuration, they allow for storing | ||
changes to a base database without changing the underlying database. | ||
Zope functional testing frameworks leverage demo storages to easily | ||
roll-back database state after a test to a non-empty state before a | ||
test. A significant limitation of demo storages is that they can't be | ||
used with base storages that change. This means that they generaly | ||
can't be used with ZEO. It isn't enough to have a read-only | ||
connections, if the underlying database is still being changed by | ||
other clients. | ||
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The "before" storage provides another way to leverage the loadBefore | ||
method to support time travel and a means to provide an unchanging | ||
view into a ZEO server. A before storage is a database adapter that | ||
provides a read-only view of an underlying storage as of a particular | ||
point in time. |
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