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### Hive Connection

Connection to the Apache Hive can be created exactly the same way as any other DB Connection. Here we make just a few Hive specific remarks you may find useful.

#### Hive JDBC Driver

The JDBC drive is part of the Hive release. But the library and its dependencies are scattered among other Hive libraries. Moreover, the driver depends on one more library from the Hadoop distribution: `hadoop-core-*.jar` or `hadoop-common-*.jar`, depending on version of your Hadoop, there's always only one of them.

For Hive version 0.8.1, here is a minimal list of libraries you need for the Hive DB connection JDBC driver:

`
hadoop-core-0.20.205.jar
hive-exec-0.8.1.jar
hive-jdbc-0.8.1.jar
hive-metastore-0.8.1.jar
hive-service-0.8.1.jar
libfb303-0.7.0.jar
slf4j-api-1.6.1.jar
slf4j-log4j12-1.6.1.jar`

You can put all of the Hive distribution libraries + the one Hadoop lib on the JDBC driver classpath. But some of the Hive distribution libraries may already be included in Clover which may result in class loading conflicts. Typically, no `commons-logging*` and `log4j*` libraries should be included, otherwise (harmless) warnings will appear in a graph run log.

#### Using Hive in Clover Transformation Graphs

Remember that Hive is not an ordinary SQL relational database, it has its own SQL-like query language, called QL. Great resource about the Hive QL and Hive in general is the Apache Hive Wiki.

One of the consequences is that it makes no sense to use the DBOutputTable component, because `INSERT INTO` statement can insert only results of a `SELECT` query. Even though it's still possible to work around this, each Clover data record inserted using such `INSERT` statement will results in a heavy-weigh MapReduce job, which renders the component painfully slow. Use `LOAD DATA` Hive QL statement instead.

In the DBExecute component, always set the Transaction set attribute to One statement. The reason is that the Hive JDBC driver doesn't support transactions, and attempt do use them would result in an error saying that the AutoCommit mode cannot be disabled.

Note that the append file operation is fully supported only since version 0.21.0 of HDFS. Consequently, if you run Hive on top of older HDFS, you cannot append data to existing tables (use of the `OVERWRITE` keyword becomes mandatory).

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