Blair Zajac created CASSANDRA-5619:
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Summary: CAS UPDATE for a lost race: save round trip by returning
column values
Key: CASSANDRA-5619
URL: https://issues.apache.org/jira/browse/CASSANDRA-5619
Project: Cassandra
Issue Type: Improvement
Components: Core
Affects Versions: 2.0
Reporter: Blair Zajac
Looking at the new CAS CQL3 support examples [1], if one lost a race for an
UPDATE, to save a round trip to get the current values to decide if you need to
perform your work, could the columns that were used in the IF clause also be
returned to the caller? Maybe the columns values as part of the SET part could
also be returned.
I don't know if this is generally useful though.
In the case of creating a new user account with a given username which is the
partition key, if one lost the race to another person creating an account with
the same username, it doesn't matter to the loser what the column values are,
just that they lost.
I'm new to Cassandra, so maybe there's other use cases, such as doing
incremental amount of work on a row. In pure Java projects I've done while
loops around AtomicReference.html#compareAndSet() until the work was done on
the referenced object to handle multiple threads each making forward progress
in updating the references object.
[1] https://github.com/riptano/cassandra-dtest/blob/master/cql_tests.py#L3044
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