12.76. Release 0.170

General Changes

Fix race condition that could cause queries to fail with InterruptedException in rare cases.
Fix a performance regression for GROUP BY queries over UNION.
Fix a performance regression that occurs when a significant number of exchange sources produce no data during an exchange (e.g., in a skewed hash join).

Fix an intermittent connection issue for Cassandra 2.1.
Remove support for selecting by partition key when the partition key is only partially specified. The cassandra.limit-for-partition-key-select and cassandra.fetch-size-for-partition-key-select config options are no longer supported.
Remove partition key cache to improve consistency and reduce load on the Cassandra cluster due to background cache refresh.
Reduce the number of connections opened to the Cassandra cluster. Now Presto opens a single connection from each node.
Use exponential backoff for retries when Cassandra hosts are down. The retry timeout can be controlled via the cassandra.no-host-available-retry-timeout config option, which has a default value of 1m. The cassandra.no-host-available-retry-count config option is no longer supported.