# cassandra.concurrent

Utilities for Concurrent Statement Execution

<a id="module-cassandra.concurrent"></a>

### cassandra.concurrent.execute_concurrent(session, statements_and_parameters, concurrency=100, raise_on_first_error=True, results_generator=False, execution_profile=<object object>)

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

The concurrency parameter controls how many statements will be executed
concurrently. It must be an integer greater than zero.

If raise_on_first_error is left as `True`, execution will stop
scheduling new statements after the first failed statement and the
corresponding exception will be raised. With results_generator, earlier
results are yielded first and the exception is raised when iteration
reaches the failed statement.

results_generator controls how the results are returned.

* If `False`, the results are returned only after all requests have completed.
* If `True`, an iterator is returned. Using a generator results in a constrained
  memory footprint when the results set will be large – results are yielded
  as they return instead of materializing the entire list at once. The trade for lower memory
  footprint is marginal CPU overhead (more thread coordination and sorting out-of-order results
  on-the-fly).

execution_profile argument is the execution profile to use for this
request, and is passed directly to `Session.execute_async()`. In
legacy configuration mode, each request uses `Session.default_timeout`;
otherwise it uses the selected execution profile’s `request_timeout`.

A sequence of `ExecutionResult(success, result_or_exc)` namedtuples 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.

Example usage:

```default
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
```

Note: in the case that generators are used, it is important to ensure the consumers do not
block or attempt further synchronous requests, because no further IO will be processed until
the consumer returns. This may also produce a deadlock in the IO event thread.

### cassandra.concurrent.execute_concurrent_with_args(session, statement, parameters, \*args, \*\*kwargs)

Like [`execute_concurrent()`](#cassandra.concurrent.execute_concurrent), but takes a single
statement and a sequence of parameters.  Each item in `parameters`
should be a sequence or `None`.

Example usage:

```default
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)
```

### cassandra.concurrent.execute_concurrent_async(session, statements_and_parameters, concurrency=100, raise_on_first_error=False, execution_profile=<object object>)

Asynchronously execute statements, returning a Future immediately.

See [`Session.execute_concurrent_async()`](https://python-driver.docs.scylladb.com/stable/api/cassandra/cluster.md#cassandra.cluster.Session.execute_concurrent_async).

#### Versionadded
Added in version 3.29.13.