Create a gist now

Instantly share code, notes, and snippets.

What would you like to do?
Batching input reader for appengine-mapreduce
class KeyRangeBatchKeyIterator(
datastore_range_iterators.AbstractKeyRangeIterator):
"""Yields datastore.Key type within a key range in batches.
This allows us to do several RPCs in parallel, hopefully reducing running
time.
TODO(colin): the query batch size is the same as the processing batch size.
Figure out if there's a benefit to changing this.
"""
_KEYS_ONLY = True
def __iter__(self):
"""Yield batches of keys for mapping.
The yielded batch is a generator, so that the query cursor doesn't move
until the mapper starts processing elements.
"""
self._query = self._key_range.make_ascending_datastore_query(
self._query_spec.entity_kind, filters=self._query_spec.filters)
while True:
keys = itertools.islice(
self._query.Run(config=datastore_query.QueryOptions(
batch_size=self._query_spec.batch_size,
keys_only=True,
start_cursor=self._cursor)),
self._query_spec.batch_size)
yield keys
if self._cursor == self._query.GetCursor():
# We haven't moved since last time, which means we're at the
# end.
break
self._cursor = self._query.GetCursor()
def _get_cursor(self):
"""Get the current query cursor.
(AbstractKeyRangeIterator method taken from KeyRangeEntityIterator.)
"""
if self._query:
return self._query.GetCursor()
return self._cursor
# Register the new iterator so that the mapreduce library knows how to create
# one from the JSON mapreduce payload.
datastore_range_iterators._KEY_RANGE_ITERATORS[
KeyRangeBatchKeyIterator.__name__] = KeyRangeBatchKeyIterator
class DatastoreKeyBatchingInputReader(
mapreduce.input_readers.RawDatastoreInputReader):
"""Mapreduce input reader that yields datastore keys in batch."""
_KEY_RANGE_ITER_CLS = KeyRangeBatchKeyIterator
The MIT License (MIT)
Copyright (c) 2015 Khan Academy
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment