Understand and resolve errors received from WebHCat on HDInsight

Learn about errors received when using WebHCat with HDInsight, and how to resolve them. WebHCat is used internally by client-side tools such as Azure PowerShell and the Data Lake Tools for Visual Studio.

What is WebHCat

WebHCat is a REST API for HCatalog, a table, and storage management layer for Apache Hadoop. WebHCat is enabled by default on HDInsight clusters, and is used by various tools to submit jobs, get job status, and so on, without logging in to the cluster.

Modifying configuration

Several of the errors listed in this document occur because a configured maximum has been exceeded. When the resolution step mentions that you can change a value, use Apache Ambari (web or REST API) to modify the value. For more information, see Manage HDInsight using Apache Ambari

Default configuration

If the following default values are exceeded, it can degrade WebHCat performance or cause errors:

Setting What it does Default value
[yarn.scheduler.capacity.maximum-applications][maximum-applications] The maximum number of jobs that can be active concurrently (pending or running) 10,000
templeton.exec.max-procs The maximum number of requests that can be served concurrently 20
[mapreduce.jobhistory.max-age-ms][max-age-ms] The number of days that job history are retained seven days

Too many requests

HTTP Status code: 429

Cause Resolution
You've exceeded the maximum concurrent requests served by WebHCat per minute (default 20) Reduce your workload to ensure that you don't submit more than the maximum number of concurrent requests or increase the concurrent request limit by modifying templeton.exec.max-procs. For more information, see Modifying configuration

Server unavailable

HTTP Status code: 503

Cause Resolution
This status code usually occurs during failover between the primary and secondary HeadNode for the cluster Wait two minutes, then retry the operation

Bad request Content: Couldn't find job

HTTP Status code: 400

Cause Resolution
Job details have been cleaned up by the job history cleaner The default retention period for job history is seven days. The default retention period can be changed by modifying mapreduce.jobhistory.max-age-ms. For more information, see Modifying configuration
Job has been killed because of a failover Retry job submission for up to two minutes
An Invalid job ID was used Check if the job ID is correct

Bad gateway

HTTP Status code: 502

Cause Resolution
Internal garbage collection is occurring within the WebHCat process Wait for garbage collection to finish or restart the WebHCat service
Time out waiting on a response from the Resource Manager service. This error can occur when the number of active applications goes the configured maximum (default 10,000) Wait for currently running jobs to complete or increase the concurrent job limit by modifying yarn.scheduler.capacity.maximum-applications. For more information, see the Modifying configuration section.
Attempting to retrieve all jobs through the GET /jobs call while Fields is set to * Don't retrieve all job details. Instead use jobid to retrieve details for jobs only greater than certain job ID. Or, don't use Fields
The WebHCat service is down during HeadNode failover Wait for two minutes and retry the operation
There are more than 500 pending jobs submitted through WebHCat Wait until currently pending jobs have completed before submitting more jobs

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.