Spanner's Globally-Distributed Database: Query Execution

This paper details the evolution of Google's Spanner, a globally-distributed database system, from a key-value store to a fully-fledged SQL system. Key improvements discussed include distributed query execution, handling of transient failures via query restarts, efficient range extraction for data retrieval, and the adoption of a common SQL dialect. The authors also explain the transition from a Bigtable-like storage format to a more efficient blockwise-columnar store (Ressi). Finally, the paper highlights lessons learned during Spanner's large-scale deployment and outlines remaining challenges.