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With more than 1200 contributors, Apache Spark is one of the most actively developed open source projects. At this scale and pace of development, mistakes are bound to happen. In this paper we present SparkFuzz, a toolkit we developed at Databricks for uncovering correctness errors in the Spark SQL engine. To guard the system against correctness errors, SparkFuzz takes a fuzzing approach to testing by generating random data and queries. Spark-Fuzz executes the generated queries on a reference database system such as PostgreSQL which is then used as a test oracle to verify the results returned by Spark SQL. We explain the approach we take to data and query generation and we analyze the coverage of SparkFuzz. We show that SparkFuzz achieves its current maximum coverage relatively fast by generating a small number of queries.

Cloud object stores such as Amazon S3 are some of the largest and most cost-effective storage systems on the planet, making them an attractive target to store large data warehouses and data lakes. Unfortunately, their implementation as key-value stores makes it difficult to achieve ACID transactions and high performance: metadata operations such as listing objects are expensive, and consistency guarantees are limited. In this paper, we present Delta Lake, an open source ACID table storage layer over cloud object stores initially developed at Databricks. Delta Lake uses a transaction log that is compacted into Apache Parquet format to provide ACID properties, time travel, and significantly faster metadata operations for large tabular datasets (e.g., the ability to quickly search billions of table partitions for those relevant to a query). It also leverages this design to provide high-level features such as automatic data layout optimization, upserts, caching, and audit logs. Delta Lake tables can be accessed from Apache Spark, Hive, Presto, Redshift and other systems. Delta Lake is deployed at thousands of Databricks customers that process exabytes of data per day, with the largest instances managing exabyte-scale datasets and billions of objects.

With more than 1200 contributors, Apache Spark is one of the most actively developed open source projects. At this scale and pace of development, mistakes are bound to happen. In this paper we present SparkFuzz, a toolkit we developed at Databricks for uncovering correctness errors in the Spark SQL engine. To guard the system against correctness errors, SparkFuzz takes a fuzzing approach to testing by generating random data and queries. Spark-Fuzz executes the generated queries on a reference database system such as PostgreSQL which is then used as a test oracle to verify the results returned by Spark SQL. We explain the approach we take to data and query generation and we analyze the coverage of SparkFuzz. We show that SparkFuzz achieves its current maximum coverage relatively fast by generating a small number of queries.