197 lines
7.1 KiB
Python
197 lines
7.1 KiB
Python
# Copyright 2013-2015 DataStax, Inc.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import six
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import sys
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from itertools import count, cycle
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import logging
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from six.moves import xrange
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from threading import Event
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from cassandra.cluster import PagedResult
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log = logging.getLogger(__name__)
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def execute_concurrent(session, statements_and_parameters, concurrency=100, raise_on_first_error=True):
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"""
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Executes a sequence of (statement, parameters) tuples concurrently. Each
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``parameters`` item must be a sequence or :const:`None`.
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A sequence of ``(success, result_or_exc)`` tuples is returned in the same
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order that the statements were passed in. If ``success`` is :const:`False`,
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there was an error executing the statement, and ``result_or_exc`` will be
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an :class:`Exception`. If ``success`` is :const:`True`, ``result_or_exc``
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will be the query result.
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If `raise_on_first_error` is left as :const:`True`, execution will stop
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after the first failed statement and the corresponding exception will be
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raised.
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The `concurrency` parameter controls how many statements will be executed
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concurrently. When :attr:`.Cluster.protocol_version` is set to 1 or 2,
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it is recommended that this be kept below 100 times the number of
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core connections per host times the number of connected hosts (see
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:meth:`.Cluster.set_core_connections_per_host`). If that amount is exceeded,
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the event loop thread may attempt to block on new connection creation,
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substantially impacting throughput. If :attr:`~.Cluster.protocol_version`
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is 3 or higher, you can safely experiment with higher levels of concurrency.
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Example usage::
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select_statement = session.prepare("SELECT * FROM users WHERE id=?")
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statements_and_params = []
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for user_id in user_ids:
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params = (user_id, )
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statements_and_params.append((select_statement, params))
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results = execute_concurrent(
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session, statements_and_params, raise_on_first_error=False)
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for (success, result) in results:
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if not success:
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handle_error(result) # result will be an Exception
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else:
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process_user(result[0]) # result will be a list of rows
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"""
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if concurrency <= 0:
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raise ValueError("concurrency must be greater than 0")
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if not statements_and_parameters:
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return []
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# TODO handle iterators and generators naturally without converting the
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# whole thing to a list. This would require not building a result
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# list of Nones up front (we don't know how many results there will be),
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# so a dict keyed by index should be used instead. The tricky part is
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# knowing when you're the final statement to finish.
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statements_and_parameters = list(statements_and_parameters)
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event = Event()
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first_error = [] if raise_on_first_error else None
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to_execute = len(statements_and_parameters)
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results = [None] * to_execute
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num_finished = count(1)
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statements = enumerate(iter(statements_and_parameters))
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for i in xrange(min(concurrency, len(statements_and_parameters))):
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_execute_next(_sentinel, i, event, session, statements, results, None, num_finished, to_execute, first_error)
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event.wait()
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if first_error:
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exc = first_error[0]
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if six.PY2 and isinstance(exc, tuple):
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(exc_type, value, traceback) = exc
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six.reraise(exc_type, value, traceback)
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else:
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raise exc
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else:
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return results
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def execute_concurrent_with_args(session, statement, parameters, *args, **kwargs):
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"""
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Like :meth:`~cassandra.concurrent.execute_concurrent()`, but takes a single
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statement and a sequence of parameters. Each item in ``parameters``
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should be a sequence or :const:`None`.
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Example usage::
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statement = session.prepare("INSERT INTO mytable (a, b) VALUES (1, ?)")
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parameters = [(x,) for x in range(1000)]
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execute_concurrent_with_args(session, statement, parameters, concurrency=50)
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"""
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return execute_concurrent(session, list(zip(cycle((statement,)), parameters)), *args, **kwargs)
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_sentinel = object()
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def _handle_error(error, result_index, event, session, statements, results,
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future, num_finished, to_execute, first_error):
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if first_error is not None:
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first_error.append(error)
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event.set()
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return
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else:
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results[result_index] = (False, error)
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if next(num_finished) >= to_execute:
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event.set()
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return
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try:
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(next_index, (statement, params)) = next(statements)
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except StopIteration:
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return
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try:
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future = session.execute_async(statement, params, timeout=None)
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args = (next_index, event, session, statements, results, future, num_finished, to_execute, first_error)
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future.add_callbacks(
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callback=_execute_next, callback_args=args,
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errback=_handle_error, errback_args=args)
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except Exception as exc:
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if first_error is not None:
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if six.PY2:
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first_error.append(sys.exc_info())
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else:
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first_error.append(exc)
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event.set()
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return
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else:
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results[next_index] = (False, exc)
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if next(num_finished) >= to_execute:
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event.set()
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return
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def _execute_next(result, result_index, event, session, statements, results,
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future, num_finished, to_execute, first_error):
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if result is not _sentinel:
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if future.has_more_pages:
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result = PagedResult(future, result)
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future.clear_callbacks()
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results[result_index] = (True, result)
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finished = next(num_finished)
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if finished >= to_execute:
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event.set()
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return
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try:
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(next_index, (statement, params)) = next(statements)
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except StopIteration:
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return
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try:
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future = session.execute_async(statement, params, timeout=None)
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args = (next_index, event, session, statements, results, future, num_finished, to_execute, first_error)
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future.add_callbacks(
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callback=_execute_next, callback_args=args,
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errback=_handle_error, errback_args=args)
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except Exception as exc:
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if first_error is not None:
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if six.PY2:
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first_error.append(sys.exc_info())
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else:
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first_error.append(exc)
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event.set()
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return
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else:
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results[next_index] = (False, exc)
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if next(num_finished) >= to_execute:
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event.set()
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return
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