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From "Paul Yang (JIRA)" <>
Subject [jira] Created: (HIVE-1219) More robust handling of metastore connection failures
Date Wed, 10 Mar 2010 03:36:27 GMT
More robust handling of metastore connection failures

                 Key: HIVE-1219
             Project: Hadoop Hive
          Issue Type: New Feature
          Components: Metastore
            Reporter: Paul Yang
            Assignee: Paul Yang
             Fix For: 0.6.0

Currently, if metastore's connection to the datastore is broken, the query fails and the exception
such as the following is thrown

2010-01-28 11:50:20,885 ERROR exec.MoveTask ( - Failed with
exception Unable to fetch table tmp_table
org.apache.hadoop.hive.ql.metadata.HiveException: Unable to fetch table tmp_table
at org.apache.hadoop.hive.ql.metadata.Hive.getTable(
at org.apache.hadoop.hive.ql.metadata.Hive.getTable(
at org.apache.hadoop.hive.ql.exec.MoveTask.execute(
at org.apache.hadoop.hive.ql.exec.Task.executeTask(
at org.apache.hadoop.hive.ql.exec.TaskRunner.runSequential(
at org.apache.hadoop.hive.ql.Driver.launchTask(
at org.apache.hadoop.hive.ql.Driver.execute(
at org.apache.hadoop.hive.ql.Driver.runCommand(
at org.apache.hadoop.hive.cli.CliDriver.processCmd(
at org.apache.hadoop.hive.cli.CliDriver.processLine(
at org.apache.hadoop.hive.cli.CliDriver.processReader(
at org.apache.hadoop.hive.cli.CliDriver.main(
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(
at sun.reflect.DelegatingMethodAccessorImpl.invoke(
at java.lang.reflect.Method.invoke(
at org.apache.hadoop.util.RunJar.main(
Caused by: javax.jdo.JDODataStoreException: Communications link failure

Last packet sent to the server was 1 ms ago.
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Last packet sent to the server was 1 ms ago.
at org.datanucleus.jdo.NucleusJDOHelper.getJDOExceptionForNucleusException(

In order to reduce the impact of transient network issues and momentarily unavailable datastores,
two possible improvements are:

1. Retrying the metastore command in case of connection failure before propagating up the

2. Retrieving the datastore hostname / connection URL through the use of an extension. This
extension would be useful in the case where a remote service maintained the location of the
currently available datastore. In case of hostname changes or failovers to a backup datastore,
the extension would allow hive clients to run without manual intervention.

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