HIve MetaStore Event Listeners are used to Detect the every single event that takes place whenever an event is executed in hive, in case You want some action to take place for an event you can override MetaStorePreEventListener and provide it your own Implementation
in this article, we will learn how to create our own metastore event listeners in the hive using scala and sbt
so let’s get started first add the following dependencies in your build.sbt file
libraryDependencies += "org.apache.hive" % "hive-exec" % "1.2.1" excludeAll ExclusionRule(organization = "org.pentaho") libraryDependencies += "org.apache.hadoop" % "hadoop-common" % "2.7.3" libraryDependencies += "org.apache.httpcomponents" % "httpclient" % "4.3.4" libraryDependencies += "org.apache.hadoop" % "hadoop-client" % "2.6.0" libraryDependencies += "org.apache.hive" % "hive-service" % "1.2.1" unmanagedJars in Compile += file("/usr/lib/hive/lib/hive-exec-1.2.1.jar") assemblyMergeStrategy in assembly := { case PathList("META-INF", xs @ _*) => MergeStrategy.discard case x => MergeStrategy.first }
now create your first class you can be named it anything I named it as OrcMetastoreListener this class must extend MetaStorePreEventListener class of hive and take Hadoop conf as the constructor argument
import org.apache.hadoop.conf.Configuration import org.apache.hadoop.hive.metastore.MetaStorePreEventListener import org.apache.hadoop.hive.metastore.events.PreEventContext.PreEventType._ import org.apache.hadoop.hive.metastore.events._ class OrcMetastoreListener(conf: Configuration) extends MetaStorePreEventListener(conf) { override def onEvent(preEventContext: PreEventContext): Unit = { preEventContext.getEventType match { case CREATE_TABLE => val tableName = preEventContext.asInstanceOf[PreCreateTableEvent].getTable tableName.getSd.setInputFormat("org.apache.hadoop.hive.ql.io.orc.OrcInputFormat") tableName.getSd.setOutputFormat("org.apache.hadoop.hive.ql.io.orc.OrcOutputFormat") case ALTER_TABLE => val newTableName = preEventContext.asInstanceOf[PreAlterTableEvent].getNewTable newTableName.getSd.setInputFormat("org.apache.hadoop.hive.ql.io.orc.OrcInputFormat") newTableName.getSd.setOutputFormat("org.apache.hadoop.hive.ql.io.orc.OrcOutputFormat") case _ => //do nothing } } }
the pre-event context contains all the hive meta store event in my case I want that whenever a table is get created in the hive it must use hive input format and output format and same thing for altering command
The best use case for this listener is when somebody wants to query a data source such as spark or any other data source using its own custom input format and even don’t want to alter the schema of hive table to use his custom input format
now let’s build a jar from the core and use it in the Hive
First, add sbt assembly plugin in your plugins.sbt file
addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.14.5")
now got to your root project and build the jar with command sbt assembly
it will build your jar, collect your jar and put it in your $HIVE_HOME/lib path
inside $HIVE_HOME/conf folder add the following contents in hive-site.xml
<configuration>
<property>
<name>javax.jdo.option.ConnectionURL</name>
<value>jdbc:derby:metastore_db;create=true</value>
<description>JDBC connect string for a JDBC metastore</description>
</property>
<property>
<name>hive.metastore.schema.verification</name>
<value>false></value>
</property>
<property>
<name>hive.metastore.pre.event.listeners</name>
<value>metastorelisteners.OrcMetastoreListener</value>
</property>
</configuration>
now create a table in hive and describe it
hive> CREATE TABLE HIVETABLE(ID INT); OK Time taken: 2.742 seconds hive> DESC EXTENDED HIVETABLE > ; OK id int Detailed Table Information Table(tableName:hivetable, dbName:default, owner:hduser,e, inputFormat:org.apache.hadoop.hive.ql.io.orc.OrcInputFormat, outputFormat:org.apache.hadoop.hive.ql.io.orc.OrcOutputFormat, compressed:false, Time taken: 0.611 seconds, Fetched: 3 row(s)
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