Apache Hive supports transactional tables which provide ACID guarantees. There has been a significant amount of work that has gone into hive to make these transactional tables highly performant. Apache Spark provides some capabilities to access hive external tables but it cannot access hive managed tables. To access hive managed tables from spark Hive Warehouse Connector needs to be used.
We are happy to announce Spark Direct Reader mode in Hive Warehouse Connector which can read hive transactional tables directly from the filesystem. This feature has been available from CDP-Public-Cloud-2.0 (188.8.131.52) and CDP-DC-7.1 (184.108.40.206) releases onwards.
Hive Warehouse Connector (HWC) was available to provide access to managed tables in hive from spark, however since this involved communication with LLAP there was an additional hop to get the data and process it in spark vs the ability of spark to directly read the data from FileSystem for External tables. This leads to performance degradation in accessing data from managed tables vs external tables. Additionally a lot of use cases for HWC were associated with ETL jobs where a super user was running these jobs to update data in multiple tables hence authorization was not a strong business need for this case. HWC Spark Direct Reader is an additional mode available in HWC which tries to address the above concerns. This article describes the usage of spark direct reader to consume hive transactional table data in a spark application. It also introduces the methods and APIs to read hive transactional tables into spark dataframes. Finally, it demonstrates the transaction handling and semantics while using this reader.
Click through to learn how it works and see it in action.