cassandra.concurrent - Utilities for Concurrent Statement Execution

cassandra.concurrent.execute_concurrent(session, statements_and_parameters, concurrency=100, raise_on_first_error=True)[source]

Executes a sequence of (statement, parameters) tuples concurrently. Each parameters item must be a sequence or None.

A sequence of (success, result_or_exc) tuples is returned in the same order that the statements were passed in. If success is False, there was an error executing the statement, and result_or_exc will be an Exception. If success is True, result_or_exc will be the query result.

If raise_on_first_error is left as True, execution will stop after the first failed statement and the corresponding exception will be raised.

The concurrency parameter controls how many statements will be executed concurrently. When Cluster.protocol_version is set to 1 or 2, it is recommended that this be kept below 100 times the number of core connections per host times the number of connected hosts (see Cluster.set_core_connections_per_host()). If that amount is exceeded, the event loop thread may attempt to block on new connection creation, substantially impacting throughput. If protocol_version is 3 or higher, you can safely experiment with higher levels of concurrency.

Example usage:

select_statement = session.prepare("SELECT * FROM users WHERE id=?")

statements_and_params = []
for user_id in user_ids:
    params = (user_id, )
    statements_and_params.append((select_statement, params))

results = execute_concurrent(
    session, statements_and_params, raise_on_first_error=False)

for (success, result) in results:
    if not success:
        handle_error(result)  # result will be an Exception
    else:
        process_user(result[0])  # result will be a list of rows
cassandra.concurrent.execute_concurrent_with_args(session, statement, parameters, *args, **kwargs)[source]

Like execute_concurrent(), but takes a single statement and a sequence of parameters. Each item in parameters should be a sequence or None.

Example usage:

statement = session.prepare("INSERT INTO mytable (a, b) VALUES (1, ?)")
parameters = [(x,) for x in range(1000)]
execute_concurrent_with_args(session, statement, parameters, concurrency=50)