Yesterday Friday on IRC, Bryan and Grant requested support for being able to
set multiple attributes "at a time" on an item. By this, they wanted a way to
turn off side-effects such as observers, monitors and index changes until all
values are set. This could have significant impact on performance by avoiding
redundant side-effects while values that belong together are set.
Implementing a general solution to this is tricky and we decided to start with
having a way to temporarily turn off index re-indexing. Python 2.5's 'with'
construct seems a good fit for this feature and I'm pleased to announce the
new reindexingDeferred() API allowing to temporarily turn off re-indexing
globally on a view:
with view.reindexingDeferred():
item.a1 = v1
item.a2 = v2
another.a3 = v3
item.a1 = v4
Inside the with-block, re-indexing is turned off and accessing indexes that
need re-indexing is denied, failing with a LookupError. Once execution exits
the block, all indexes that need re-indexing are re-indexed automatically.
The performance advantage of this construct is that redundant re-indexing
operations are discarded, only the last re-indexing change for a given item in
a given index is kept.
These "with view.reindexingDeferred():" blocks can be nested, only when the
outer one completes, the re-indexing takes place.
In order to support this feature, I had to rework index monitor support quite
a bit. The Item._reIndex() method (that was overridden in collections.py) is
gone and replaced by an optional onCollectionReindex() hook method.
See parcels/osaf/pim/collections.py for an example implementation.
Questions, comments are welcome.
Should I implement "with view.observersDeferred():" next ?
It could be nested with "with view.reindexingDeferred():" and the order of
nesting would give some control over which side-effects are turned on and off
and when.
Andi..
ps: to use the 'with' statement in python 2.5, you need to have a
from __future__ import with_statement
statement as the first python statement in your file.
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