Getting Exception while inserting using bucket.async.insert

yes. The list coming was empty. Thanks. When i try to write large volume of documents(3 to 4 lac documets) this operation gets hung after sometime. i see the below messages. Any idea what is going wrong here?

10:48:56.515 [cb-io-1-1] DEBUG c.c.c.c.endpoint.kv.KeyValueHandler - [localhost/127.0.0.1:11210][KeyValueEndpoint]: Identified Idle State, signalling config reload.
10:48:56.515 [cb-io-1-1] DEBUG c.c.c.c.e.AbstractGenericHandler - [localhost/127.0.0.1:11210][KeyValueEndpoint]: KeepAlive fired
10:48:56.515 [cb-core-3-1] DEBUG c.c.c.c.config.ConfigurationProvider - Received signal for outdated configuration.
10:48:56.527 [cb-computations-2] DEBUG c.c.c.c.config.ConfigurationProvider - New Bucket contact-service-data config proposed.
10:48:56.529 [cb-computations-2] DEBUG c.c.c.c.c.refresher.CarrierRefresher - Completed refreshing config for bucket “contact-service-data”