Use MySQL for the Hive Metastore

The metadata for Hive tables and partitions are stored in the Hive Metastore. By default, the Hive Metastore stores all Hive metadata in an embedded Apache Derby database in the HPE Ezmeral Data Fabric filesystem. Derby only allows one connection at a time; if you want multiple concurrent Hive sessions, you can use MySQL for the Hive Metastore.

Review the following prerequisites before you begin:

Verify that MySQL (version 5.6.17 or later) is installed on the machine that will host the Hive metastore, and also verify that you can connect to the MySQL server from the Hive machine. You can run the Hive metastore on any machine that is accessible from Hive. You can test this with the following command:
```
mysql -h <hostname> -u <user>
```
The database administrator must create a database for the Hive metastore data, and the username specified in javax.jdo.option.ConnectionUserName must have permissions to access it. The database can be specified using the ConnectionURL parameter. The tables and schemas are created automatically when the metastore is first started.

Tip: In MapR 6.1.0 and earlier releases, the following steps can be used interchangeably for MariaDB.

Complete the following steps to configure Hive to use MySQL for the Hive Metastore:

Important: For MySQL 8, set the javax.jdo.option.ConnectionDriverName property to com.mysql.cj.jdbc.Driver. The com.mysql.jdbc.Driver is deprecated. The new driver class is com.mysql.cj.jdbc.Driver. However, the driver is automatically registered via the Service Provider Interface, so manual loading of the driver class is generally unnecessary.

Update the hive-site.xml in the Hive configuration directory (/opt/mapr/hive/hive-<version>/conf) with the following contents:

<configuration>

 <property>
    <name>javax.jdo.option.ConnectionURL</name>
    <value>jdbc:mysql://localhost:3306/hive?createDatabaseIfNotExist=true</value>
    <description>JDBC connect string for a JDBC metastore</description>
</property>

 <property>
    <name>javax.jdo.option.ConnectionDriverName</name>
    <value>com.mysql.jdbc.Driver</value>
    <description>Driver class name for a JDBC metastore</description>
 </property>

 <property>
    <name>javax.jdo.option.ConnectionUserName</name>
    <value>root</value>
    <description>username to use against metastore database</description>
 </property>

 <property>
    <name>javax.jdo.option.ConnectionPassword</name>
    <value><fill in with password></value>
    <description>password to use against metastore database</description>
 </property>

 <property>
    <name>hive.metastore.uris</name>
    <value>thrift://localhost:9083</value>
 </property>

</configuration>

Run the schematool command as an initialization step.

/opt/mapr/hive/hive-<version>/bin/schematool -dbType mysql -initSchema

To connect to an existing MySQL metastore, make sure the ConnectionURL parameter and the Thrift URIs parameters in hive-site.xml point to the metastore's host and port.
To set a specific port for Thrift URIs, add the command export METASTORE_PORT=<port> into the file hive-env.sh (if hive-env.sh does not exist, create it in the Hive configuration directory). Example:
```
export METASTORE_PORT=9083
```
Start the Hive Metastore service using one of the following commands:
If you want the Hive Metastore to be managed by Warden, the maprcli, and the Control System:
```
maprcli node services -name hivemeta -action start -nodes <space delimited list of nodes> 
```
If you want the Hive Metastore to be managed with standard hive commands:
```
/opt/mapr/hive/hive-<version>/bin/hive --service metastore --start
```
You can use also use nohup hive --service metastore to run the Metastore in the background.
Warning: If you have not configured a MySQL Metastore, do not run the Hive shell from an NFS mount location. If you try to do this, Hive will fail. The same problem will occur if you use the hive-site.xml file to configure the Metastore on an NFS mount location. Avoid both of these configurations.