client_session – Logical sessions for sequential operations

Logical sessions for ordering sequential operations.

Requires MongoDB 3.6.

New in version 3.6.

Causally Consistent Reads

with client.start_session(causal_consistency=True) as session:
    collection = client.db.collection
    collection.update_one({'_id': 1}, {'$set': {'x': 10}}, session=session)
    secondary_c = collection.with_options(
        read_preference=ReadPreference.SECONDARY)

    # A secondary read waits for replication of the write.
    secondary_c.find_one({'_id': 1}, session=session)

If causal_consistency is True (the default), read operations that use the session are causally after previous read and write operations. Using a causally consistent session, an application can read its own writes and is guaranteed monotonic reads, even when reading from replica set secondaries.

See also

The MongoDB documentation on

causal-consistency

Classes

class pymongo.client_session.ClientSession(client, server_session, options, authset)

A session for ordering sequential operations.

advance_cluster_time(cluster_time)

Update the cluster time for this session.

Parameters:

• cluster_time: The cluster_time from another ClientSession instance.

advance_operation_time(operation_time)

Update the operation time for this session.

Parameters:

• operation_time: The operation_time from another ClientSession instance.

client

The MongoClient this session was created from.

cluster_time

The cluster time returned by the last operation executed in this session.

end_session()

Finish this session.

It is an error to use the session or any derived Database, Collection, or Cursor after the session has ended.

has_ended

True if this session is finished.

operation_time

The operation time returned by the last operation executed in this session.

options

The SessionOptions this session was created with.

session_id

A BSON document, the opaque server session identifier.

class pymongo.client_session.SessionOptions(causal_consistency=True)

Options for a new ClientSession.

Parameters:

• causal_consistency (optional): If True (the default), read operations are causally ordered within the session.

causal_consistency

Whether causal consistency is configured.