Hive Warehouse Connector for accessing Apache Spark data

The Hive Warehouse Connector (HWC) is a Spark library/plugin that is launched with the Spark app. You can use the Hive Warehouse Connector API to access any managed Hive table from Spark. Apache Ranger and the HiveWarehouseConnector library provide row and column, fine-grained access to the data.

In CDP Public Cloud and CDP Data Center, Spark and Hive share a catalog in the Hive metastore (HMS).

CDP Public Cloud Processing

In CDP Public Cloud, to read ACID, or other Hive-managed tables, from Spark using low-latency analytical processing (LLAP) is recommended.

To write to ACID, or other managed tables, from Spark you must use JDBC. HWC is not required to access external tables from Spark. Spark can directly access Hive external tables using spark sql instead of HWC. However, HWC also supports reading external tables.

Using the HWC, you can read and write Apache Spark DataFrames and Streaming DataFrames.

CDP Data Center Processing

In CDP Data Center, HWC is available as a technical preview. HWC processes data through the Hive JDBC driver (download the latest 2.6.x version). LLAP is not available in CDP Data Center. You can choose cluster processing (recommended) or in-memory client processing, depending on the size of your resultset and latency requirements. Cluster processing, described later, is recommended for ingesting large data sets.

Configure the JDBC mode for in-memory processing. HWC stores the entire resultset in an in-memory cache for fast processing. The capacity of the in-memory cache is limited based on the capacity of the Spark driver/client application.

HWC Limitations

HWC supports reading tables in any format, but currently supports writing tables in ORC format only.
Table stats (basic stats and column stats )are not generated when you write a DataFrame to Hive.
The spark thrift server is not supported.
The Hive Union data type is not supported.
Transaction semantics of Spark RDDs are not ensured when using Spark Direct Reader to read ACID tables.
When the HWC API save mode is overwrite, writes are limited.
You cannot read from and overwrite the same table. If your query accesses only one table and you try to overwrite that table using an HWC API write method, a deadlock state might occur. Do not attempt this operation.
Example: Operation Not Supported
```
scala> val df = hive.executeQuery("select * from t1")
scala> df.write.format("com.hortonworks.spark.sql.hive.llap.HiveWarehouseConnector").mode("overwrite").option("table", "t1").save          
```

Supported applications and operations

The Hive Warehouse Connector supports the following applications:

Spark shell
PySpark
The spark-submit script

The following list describes a few of the operations supported by the Hive Warehouse Connector:

Describing a table
Creating a table in ORC using .createTable() or in any format using .executeUpdate()
Writing to a table in ORC format
Selecting Hive data and retrieving a DataFrame
Writing a DataFrame to a Hive-managed ORC table in batch
Executing a Hive update statement
Reading table data, transforming it in Spark, and writing it to a new Hive table
Writing a DataFrame or Spark stream to Hive using HiveStreaming
Partitioning data when writing a DataFrame