Hive Metastore Administration
Introduction
All the metadata for Hive tables and partitions are stored in Hive Metastore. Metadata is persisted using JPOX ORM solution so any store that is supported by it can be used by Hive. Most of the commercial relational databases and many open source datstores are supported. Any datastore that has a JDBC driver can probably be used.
You can find an E/R diagram for the metastore here.
There are 3 different ways to setup the metastore server using different Hive configurations:
The relevant configuration parameters are shown here. (Non-metastore parameters are described in Configuring Hive. Also see the Language Manual's Hive Configuration Properties, including Metastore and Hive Metastore Security.)
Config Param | Description |
|---|---|
javax.jdo.option.ConnectionURL | JDBC connection string for the data store which contains metadata |
javax.jdo.option.ConnectionDriverName | JDBC Driver class name for the data store which contains metadata |
hive.metastore.uris | Hive connects to one of these URIs to make metadata requests to a remote Metastore (comma separated list of URIs) |
hive.metastore.local | local or remote metastore (Removed as of Hive 0.10: If |
hive.metastore.warehouse.dir | URI of the default location for native tables |
The Hive Metastore is stateless and thus there can be multiple instances to achieve High Availability. Using hive.metastore.uris it is possible to specify multiple remote Metastores. Hive will use the first one from the list by default but will pick a random one on connection failure and will try to reconnect.
These variables were carried over from old documentation without a guarantee that they all still exist (see the HiveConf java class for current Hive configuration options):
Variable Name | Description | Default Value |
|---|---|---|
hive.metastore.metadb.dir |
|
|
hive.metastore.rawstore.impl | (Hive 0.8.1 and later.) |
|
org.jpox.autoCreateSchema | Creates necessary schema on startup if one doesn't exist. (e.g. tables, columns...) Set to false after creating it once. |
|
org.jpox.fixedDatastore | Whether the datastore schema is fixed. |
|
datanucleus.autoStartMechanism | Whether to initialize on startup. |
|
hive.metastore.ds.connection.url.hook | Name of the hook to use for retriving the JDO connection URL. If empty, the value in javax.jdo.option.ConnectionURL is used as the connection URL. (Hive 0.6 and later.) |
|
hive.metastore.ds.retry.attempts | The number of times to retry a call to the backing datastore if there were a connection error. (Hive 0.6 and later; deprecated in Hive 0.13.0 – use hive.hmshandler.retry.attempts instead.) | 1 |
hive.metastore.ds.retry.interval | The number of miliseconds between datastore retry attempts. (Hive 0.6 and later; deprecated in Hive 0.13.0 – use hive.hmshandler.retry.interval instead.) | 1000 |
hive.metastore.server.min.threads | Minimum number of worker threads in the Thrift server's pool. (Hive 0.6 and later.) | 200 |
hive.metastore.server.max.threads | Maximum number of worker threads in the Thrift server's pool. (Hive 0.6 and later.) | 100000 since Hive 0.8.1 |
Configuring datanucleus.autoStartMechanism is highly recommended
Configuring auto start for data nucleus is highly recommended. See HIVE-4762 for more details.
<property>
<name>datanucleus.autoStartMechanism</name>
<value>SchemaTable</value>
</property>
Default configuration sets up an embedded metastore which is used in unit tests and is described in the next section. More practical options are described in the subsequent sections.
Embedded Metastore
An embedded metastore is mainly used for unit tests. Only one process can connect to the metastore at a time, so it is not really a practical solution but works well for unit tests.
Derby is the default database for the embedded metastore.
Config Param | Config Value | Comment |
|---|---|---|
javax.jdo.option.ConnectionURL |
| Derby database located at hive/trunk/build... |
javax.jdo.option.ConnectionDriverName |
| Derby embeded JDBC driver class |
hive.metastore.uris | not needed since this is a local metastore |
|
hive.metastore.local |
| embeded is local |
hive.metastore.warehouse.dir |
| unit test data goes in here on your local filesystem |
If you want to run Derby as a network server so the metastore can be accessed from multiple nodes, see Hive Using Derby in Server Mode.
Local Metastore
In local metastore setup, each Hive Client will open a connection to the datastore and make SQL queries against it. The following configuration will set up a metastore in a MySQL server. Make sure that the server is accessible from the machines where Hive queries are executed since this is a local store. Also make sure the JDBC client library is in the classpath of Hive Client.
Config Param | Config Value | Comment |
|---|---|---|
javax.jdo.option.ConnectionURL |
| metadata is stored in a MySQL server |
javax.jdo.option.ConnectionDriverName |
| MySQL JDBC driver class |
javax.jdo.option.ConnectionUserName |
| user name for connecting to MySQL server |
javax.jdo.option.ConnectionPassword |
| password for connecting to MySQL server |
hive.metastore.uris | not needed because this is local store |
|
hive.metastore.local |
| this is local store |
hive.metastore.warehouse.dir |
| default location for Hive tables. |
Remote Metastore
In remote metastore setup, all Hive Clients will make a connection to a metastore server which in turn queries the datastore (MySQL in this example) for metadata. Metastore server and client communicate using Thrift Protocol. Starting with Hive 0.5.0, you can start a Thrift server by executing the following command:
hive --service metastore
In versions of Hive earlier than 0.5.0, it's instead necessary to run the Thrift server via direct execution of Java:
$JAVA_HOME/bin/java -Xmx1024m -Dlog4j.configuration=file://$HIVE_HOME/conf/hms-log4j.properties -Djava.library.path=$HADOOP_HOME/lib/native/Linux-amd64-64/ -cp $CLASSPATH org.apache.hadoop.hive.metastore.HiveMetaStore
If you execute Java directly, then JAVA_HOME, HIVE_HOME, HADOOP_HOME must be correctly set; CLASSPATH should contain Hadoop, Hive (lib and auxlib), and Java jars.
Server Configuration Parameters
Config Param | Config Value | Comment |
|---|---|---|
javax.jdo.option.ConnectionURL |
| metadata is stored in a MySQL server |
javax.jdo.option.ConnectionDriverName |
| MySQL JDBC driver class |
javax.jdo.option.ConnectionUserName |
| user name for connecting to MySQL server |
javax.jdo.option.ConnectionPassword |
| password for connecting to MySQL server |
hive.metastore.warehouse.dir |
| default location for Hive tables. |
Client Configuration Parameters
Config Param | Config Value | Comment |
|---|---|---|
hive.metastore.uris |
| host and port for the Thrift metastore server |
hive.metastore.local |
| This is local store. Note: This is no longer needed as of Hive 0.10. Setting hive.metastore.uris is sufficient. |
hive.metastore.warehouse.dir |
| default location for Hive tables. |
If you are using MySQL as the datastore for metadata, put MySQL client libraries in HIVE_HOME/lib before starting Hive Client or HiveMetastore Server.
To change the metastore port, use this hive command:
hive --service metastore -p <port_num>
Supported Backend Databases for Metastore
| Database | Minimum Supported Version | Name for Parameter Values |
|---|---|---|
| MySQL | 5.6.17 | mysql |
| Postgres | 9.1.13 | postgres |
| Oracle | 11g | oracle |
| MS SQL Server | 2008 R2 | mssql |
Metastore Schema Consistency and Upgrades
Version
Introduced in Hive 0.12.0. See HIVE-3764.
Hive now records the schema version in the metastore database and verifies that the metastore schema version is compatible with Hive binaries that are going to accesss the metastore. Note that the Hive properties to implicitly create or alter the existing schema are disabled by default. Hive will not attempt to change the metastore schema implicitly. When you execute a Hive query against an old schema, it will fail to access the metastore.
To suppress the schema check and allow the metastore to implicitly modify the schema, you need to set a configuration property hive.metastore.schema.verification to false in hive-site.xml.
Starting in release 0.12, Hive also includes an off-line schema tool to initialize and upgrade the metastore schema. Please refer to the details here.