General Changes

• Fix planning bug with NULL literal coercions.
• Reduce query startup time by reducing lock contention in scheduler.

New Hive Parquet Reader

We have added a new Parquet reader implementation. The new reader supports vectorized reads, lazy loading, and predicate push down, all of which make the reader more efficient and typically reduces wall clock time for a query. Although the new reader has been heavily tested, it is an extensive rewrite of the Apache Hive Parquet reader, and may have some latent issues, so it is not enabled by default. If you are using Parquet we suggest you test out the new reader on a per-query basis by setting the <hive-catalog>.parquet_optimized_reader_enabled session property, or you can enable the reader by default by setting the Hive catalog property hive.parquet-optimized-reader.enabled=true. To enable Parquet predicate push down there is a separate session property <hive-catalog>.parquet_predicate_pushdown_enabled and configuration property hive.parquet-predicate-pushdown.enabled=true.