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From "Paul Yang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1219) More robust handling of metastore connection failures
Date Wed, 17 Mar 2010 20:33:27 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1219?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12846571#action_12846571

Paul Yang commented on HIVE-1219:

Good catch! It would be nice if the convention were to have a separator between the words.

> More robust handling of metastore connection failures
> -----------------------------------------------------
>                 Key: HIVE-1219
>                 URL: https://issues.apache.org/jira/browse/HIVE-1219
>             Project: Hadoop Hive
>          Issue Type: New Feature
>          Components: Metastore
>            Reporter: Paul Yang
>            Assignee: Paul Yang
>             Fix For: 0.6.0
>         Attachments: HIVE-1219.1.patch, HIVE-1219.2.patch, HIVE-1219.3.patch, HIVE-1219.4.patch
> Currently, if metastore's connection to the datastore is broken, the query fails and
the exception such as the following is thrown
> {code}
> 2010-01-28 11:50:20,885 ERROR exec.MoveTask (SessionState.java:printError(248)) - 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(Hive.java:362)
> at org.apache.hadoop.hive.ql.metadata.Hive.getTable(Hive.java:333)
> at org.apache.hadoop.hive.ql.exec.MoveTask.execute(MoveTask.java:112)
> at org.apache.hadoop.hive.ql.exec.Task.executeTask(Task.java:99)
> at org.apache.hadoop.hive.ql.exec.TaskRunner.runSequential(TaskRunner.java:64)
> at org.apache.hadoop.hive.ql.Driver.launchTask(Driver.java:582)
> at org.apache.hadoop.hive.ql.Driver.execute(Driver.java:462)
> at org.apache.hadoop.hive.ql.Driver.runCommand(Driver.java:324)
> at org.apache.hadoop.hive.ql.Driver.run(Driver.java:312)
> at org.apache.hadoop.hive.cli.CliDriver.processCmd(CliDriver.java:123)
> at org.apache.hadoop.hive.cli.CliDriver.processLine(CliDriver.java:181)
> at org.apache.hadoop.hive.cli.CliDriver.processReader(CliDriver.java:200)
> at org.apache.hadoop.hive.cli.CliDriver.main(CliDriver.java:256)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
> at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> at java.lang.reflect.Method.invoke(Method.java:597)
> at org.apache.hadoop.util.RunJar.main(RunJar.java:156)
> Caused by: javax.jdo.JDODataStoreException: Communications link failure
> Last packet sent to the server was 1 ms ago.
> NestedThrowables:
> 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(NucleusJDOHelper.java:289)
> {code}
> 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 exception.
> 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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