Resolving HBase Region Transition and Hadoop File System Permission Issues in a PROD Environment

Problem:

The client encountered a critical issue in their production environment involving HBase regions stuck in a transition state. This problem resulted in service disruptions within their Hadoop cluster. The issue was exacerbated by file system permission changes following a cold restart of the cluster, leading to difficulties in accessing data and managing HBase operations. The root cause was unclear, and the client needed a reliable solution to resolve the region transitions and stabilize the cluster.

Process:

Step 1: Initial Assessment:

The client first reported that several HBase regions were stuck in a transition state. The expert team requested further details, including the events preceding the issue (such as node restarts or power outages) and specific information about the cluster’s size, number of nodes, data volume, and regions. The client shared screenshots of the HBase master and NameNode UIs, along with logs from the affected nodes.

Upon analyzing the logs, the expert identified a potential misconfiguration in the bucket cache, with errors such as:

WARN [main-BucketCacheWriter-1] bucket.BucketCache: Failed allocation for e512eff157f14c068975827312b8efc8_4533904296; org.apache.hadoop.hbase.io.hfile.bucket.BucketAllocatorException: Allocation too big size=603797;

This indicated that the cache allocation sizes were too small for certain data blocks, leading to region transitions.

Step 2: Investigative Actions:

To address the issue, the experts asked the client to review their ‘hbase.bucketcache.bucket.sizes’ in ‘hbase-site.xml’. Additionally, they suggested running the following HBase shell commands to unassign and reassign the problematic regions:

• unassign 'aaf284e84195decc90328e51227723dc', true;
• assign 'aaf284e84195decc90328e51227723dc';

The client followed these steps, running the commands repeatedly for over a day, which eventually helped resolve the transition issue.

Step 3: File System Permission Problems:

During the investigation, the client also raised concerns about file system permissions being altered after an OS upgrade and subsequent cluster restart. The expert traced this to possible manual interventions or incorrect startup scripts affecting HDFS folder permissions.

To prevent such issues in the future, the expert recommended conducting an internal audit and reviewing startup scripts that might be altering permissions unnecessarily. They also advised against restarting the entire HDFS and instead fixing permissions using specific HDFS commands.

Step 4: Root Cause Analysis and Recommendations:

During a follow-up call, the expert provided an overview of potential causes for the problem. The most likely reasons for the region transitions and permission changes were:

• Misconfigured bucket cache sizes leading to region instability.
• A faulty startup script or human error causing file system permissions to change after the cluster restart.
• The possibility of an incorrect Kerberos ticket being obtained before the cluster was brought back online.

The expert suggested several action items to improve the cluster’s stability:

• Conduct an internal audit to check if permissions were manually changed after the startup.
• Review startup scripts to ensure they aren’t unnecessarily modifying file system permissions.
• Consider adding more data nodes to balance the load, as several nodes were more than 80% full, potentially causing further instability.
• Provide full logs from all Hadoop and HBase components for a deeper analysis.

Solution:

The client resolved the HBase region transitions by manually unassigning and reassigning the regions in transition, which brought the cluster back to normal operation. Additionally, the client manually corrected the HDFS file system permissions, stabilizing the Hadoop environment after the cold restart. The expert’s recommendations to review startup scripts and conduct audits were key to preventing similar issues in the future.

Conclusion:

The expert-guided troubleshooting helped the client resolve critical HBase and Hadoop issues, ensuring the cluster returned to stable operation. The root cause analysis and recommendations provided valuable insights for the client, helping them avoid similar problems in the future and reinforcing the importance of properly managing bucket cache configurations and file system permissions in a large-scale distributed environment.