Columnar engine for Spanner is now in Public Preview. Columnar

## Feature Feature Columnar engine for Spanner is now in [Public Preview](https://cloud.google.com/products#product-launch-stages). Columnar engine is a storage technique used with analytical queries to speed up scans up to 200 times faster on live operational data without affecting transaction workloads. In databases or tables enabled with columnar engine, this release: * Supports the ability to execute columnar queries automatically and perform faster columnar scans using vectorized execution. * Provides a new [major compaction API](https://cloud.google.com/spanner/docs/manual-data-compaction)to accelerate the conversion of non-columnar data into columnar data. For more information, see the[Columnar engine for Spanner overview](https://cloud.google.com/spanner/docs/columnar-engine).