Exposed transaction reset functionality in datastore_rpc.py, and added ability for TransactionalConnection to be rollback() after failed commit().
Exposed transaction reset functionality in datastore_rpc.py, and added ability for TransactionalConnection to be rollback() after failed commit().

TransactionalConnection previously didn't allow rollback after any commit operation, even if it failed. Ideally the client should be able to roll back failed commits to free up state on the server.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=147885281

GoogleCloudPlatform/datastore-ndb-python,GoogleCloudPlatform/datastore-ndb-python