Use ImmutableEnumSet
Fix use of closed RecordReader
Introduce Signature object for functions
Refactor LocalExecutionPlanner

Replace Multimap with Map, now that all our channels contain only a
single symbol
Add unit test for DISTINCT aggregation on a JOIN
Add catalog and schema to jdbc string
Add documentation for JDBC driver
Add 0.57 release notes
Update snapshot dependencies
[maven-release-plugin] prepare release 0.57
[maven-release-plugin] prepare for next development iteration
Fix formatting and optimize imports
Fix variable naming
Make utility classes final with private constructor
Add Checkstyle configuration
Fix a bunch of formatting errors
Fix warnings in Hive file format tests
Add Cassandra connector
Split CassandraClient into separate services
Add unit test with synthetic test data