Additional statistics about a commit.
.. attribute:: mutation_count
The total number of mutations for the transaction. Knowing
the mutation_count value can help you maximize the
number of mutations in a transaction and minimize the number
of API round trips. You can also monitor this value to
prevent transactions from exceeding the system
limit <http://cloud.google.com/spanner/quotas#limits_for_creating_reading_updating_and_deleting_data>.
If the number of mutations exceeds the limit, the server
returns
INVALID_ARGUMENT <http://cloud.google.com/spanner/docs/reference/rest/v1/Code#ENUM_VALUES.INVALID_ARGUMENT>.
