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Apache HBase Master (HMaster) fails to start in Azure HDInsight

  • Artikkeli

This article describes troubleshooting steps and possible resolutions for issues when interacting with Azure HDInsight clusters.

Scenario: Master startup cannot progress, in holding-pattern until region comes online

Issue

HMaster fails to start due to the following warning:

hbase:namespace,,<timestamp_region_create>.<encoded_region_name>.is NOT online; state={<encoded_region_name> state=OPEN, ts=<some_timestamp>, server=<server_name>}; ServerCrashProcedures=true. Master startup cannot progress, in holding-pattern until region onlined.

For example, the parameter values may vary in the actual message:

hbase:namespace,,1546588612000.0000010bc582e331e3080d5913a97000. is NOT online; state={0000010bc582e331e3080d5913a97000 state=OPEN, ts=1633935993000, server=<wn fqdn>,16000,1622012792000}; ServerCrashProcedures=false. Master startup cannot progress, in holding-pattern until region onlined.

Cause

HMaster checks the WAL directory on the region servers before bringing back the OPEN regions online. In this case, if that directory wasn't present, it was not getting started

Resolution

  1. Create this dummy directory using the command: sudo -u hbase hdfs dfs -mkdir /hbase-wals/WALs/<wn fqdn>,16000,1622012792000

  2. Restart the HMaster service from the Ambari UI.

If you're using hbase-2.x, see more information in how to use hbck2 to assign namespace and meta table

Scenario: Atomic renaming failure

Issue

Unexpected files identified during startup process.

Cause

During the startup process, HMaster performs many initialization steps, including moving data from scratch (.tmp) folder to data folder. HMaster also looks at the write-ahead logs (WAL) folder to see if there are any unresponsive region servers.

HMaster does a basic list command on the WAL folders. If at any time, HMaster sees an unexpected file in any of these folders, it throws an exception and doesn't start.

Resolution

Check the call stack and try to determine which folder might be causing the problem (for instance, it might be the WAL folder or the .tmp folder). Then, in Azure Storage Explorer or by using HDFS commands, try to locate the problem file. Usually, this file is called *-renamePending.json. (The *-renamePending.json file is a journal file that's used to implement the atomic rename operation in the WASB driver. Due to bugs in this implementation, these files can be left over after process crashes, and so on.) Force-delete this file either in Cloud Explorer or by using HDFS commands.

Sometimes, there might also be a temporary file named something like $$$.$$$ at this location. You have to use HDFS ls command to see this file; you can't see the file in Azure Storage Explorer. To delete this file, use the HDFS command hdfs dfs -rm /\<path>\/\$\$\$.\$\$\$.

After you've run these commands, HMaster should start immediately.

Scenario: No server address listed

Issue

You might see a message that indicates that the hbase: meta table isn't online. Running hbck might report that hbase: meta table replicaId 0 is not found on any region. In the HMaster logs, you might see the message: No server address listed in hbase: meta for region hbase: backup <region name>.

Cause

HMaster couldn't initialize after restarting HBase.

Resolution

  1. In the HBase shell, enter the following commands (change actual values as applicable):

    scan 'hbase:meta'
delete 'hbase:meta','hbase:backup <region name>','<column name>'

  2. Delete the hbase: namespace entry. This entry might be the same error that's being reported when the hbase: namespace table is scanned.

  3. Restart the active HMaster from Ambari UI to bring up HBase in running state.

  4. In the HBase shell, to bring up all offline tables, run the following command:

    hbase hbck -ignorePreCheckPermission -fixAssignments

Scenario: java.io.IOException: Timedout

Issue

HMaster times out with fatal exception similar to: java.io.IOException: Timedout 300000ms waiting for namespace table to be assigned.

Cause

You might experience this issue if you have many tables and regions that haven't been flushed when you restart your HMaster services. The time-out is a known defect with HMaster. General cluster startup tasks can take a long time. HMaster shuts down if the namespace table isn’t yet assigned. The lengthy startup tasks happen where large amount of unflushed data exists and a timeout of five minutes isn't sufficient.

Resolution

  1. From the Apache Ambari UI, go to HBase > Configs. In the custom hbase-site.xml file, add the following setting:

    Key: hbase.master.namespace.init.timeout Value: 2400000

  2. Restart the required services (HMaster, and possibly other HBase services).

Scenario: Frequent region server restarts

Issue

Nodes reboot periodically. From the region server logs you may see entries similar to:

2017-05-09 17:45:07,683 WARN  [JvmPauseMonitor] util.JvmPauseMonitor: Detected pause in JVM or host machine (eg GC): pause of approximately 31000ms
2017-05-09 17:45:07,683 WARN  [JvmPauseMonitor] util.JvmPauseMonitor: Detected pause in JVM or host machine (eg GC): pause of approximately 31000ms
2017-05-09 17:45:07,683 WARN  [JvmPauseMonitor] util.JvmPauseMonitor: Detected pause in JVM or host machine (eg GC): pause of approximately 31000ms

Cause: zookeeper session timeout

Long regionserver JVM GC pause. The pause causes regionserver to be unresponsive and not able to send heart beat to HMaster within the zookeeper session timeout 40s. HMaster believes regionserver is dead, aborts the regionserver and restarts.

To mitigate, change the Zookeeper session timeout, not only hbase-site setting zookeeper.session.timeout but also Zookeeper zoo.cfg setting maxSessionTimeout need to be changed.

  1. Access Ambari UI, go to HBase -> Configs -> Settings, in Timeouts section, change the value of Zookeeper Session Timeout.

  2. Access Ambari UI, go to Zookeeper -> Configs -> Custom zoo.cfg, add/change the following setting. Make sure the value is the same as HBase zookeeper.session.timeout.

    Key: maxSessionTimeout Value: 120000

  3. Restart required services.

Cause: overloaded RegionServer

Follow Number of regions per RS - upper bound to calculate upper bound. For example: 8000 (Region server Heap -- Xmx in MB) * 0.4 (hbase.regionserver.global.memstore.size) /64 (hbase.regionserver.hlog.blocksize/2) = 50

To mitigate, scale up your HBase cluster.

Scenario: Log splitting failure

Issue

HMasters failed to come up on a HBase cluster.

Cause

Misconfigured HDFS and HBase settings for a secondary storage account.

Resolution

set hbase.rootdir: wasb://@.blob.core.windows.net/hbase and restart services on Ambari.

Next steps

If you didn't see your problem or are unable to solve your issue, visit one of the following channels for more support:

  • Get answers from Azure experts through Azure Community Support.

  • Connect with @AzureSupport - the official Microsoft Azure account for improving customer experience. Connecting the Azure community to the right resources: answers, support, and experts.

  • If you need more help, you can submit a support request from the Azure portal. Select Support from the menu bar or open the Help + support hub. For more detailed information, review How to create an Azure support request. Access to Subscription Management and billing support is included with your Microsoft Azure subscription, and Technical Support is provided through one of the Azure Support Plans.