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📌 Some insights on Namenode failure management in Hadoop 📢

✔ Managing NameNode failures in Hadoop is crucial to ensure high availability and fault tolerance in the Hadoop Distributed File System (HDFS).

✔ The NameNode is a critical component in HDFS as it stores the metadata of the file system, including file locations, permissions, and block information. If the NameNode fails, the entire HDFS becomes inaccessible, leading to data unavailability and potential data loss.

✅ 𝐇𝐚𝐝𝐨𝐨𝐩 𝐇𝐢𝐠𝐡 𝐀𝐯𝐚𝐢𝐥𝐚𝐛𝐢𝐥𝐢𝐭𝐲 (𝐇𝐀):

▪ Hadoop High Availability (HA) is a feature introduced to ensure continuous availability of the HDFS, even in the event of a NameNode failure.

▪ HA involves having two active NameNodes in the cluster: the Active NameNode and the Standby NameNode. The Active NameNode handles all client requests and performs read and write operations on the file system.

▪ The Standby NameNode stays in sync with the Active NameNode by continuously replicating its namespace edits and block information.

▪ In the event of a failure of the Active NameNode, the Standby NameNode is automatically promoted to become the new Active NameNode, ensuring seamless failover.

▪ The process is transparent to clients and requires minimal downtime, providing high availability for the HDFS.

✅ 𝐐𝐮𝐨𝐫𝐮𝐦 𝐉𝐨𝐮𝐫𝐧𝐚𝐥 𝐌𝐚𝐧𝐚𝐠𝐞𝐫 (𝐐𝐉𝐌):

▪ To keep the Standby NameNode up-to-date with the Active NameNode's changes, Hadoop uses a Quorum Journal Manager (QJM).

▪ The QJM is a distributed storage system that stores the edit logs generated by the Active NameNode. Both the Active NameNode and the Standby NameNode have access to the QJM, which ensures that the Standby NameNode can always retrieve the latest edit logs and keep its metadata up-to-date.

✅ 𝐏𝐞𝐫𝐢𝐨𝐝𝐢𝐜 𝐂𝐡𝐞𝐜𝐤𝐩𝐨𝐢𝐧𝐭𝐢𝐧𝐠:

▪ Checkpointing is a process of saving the HDFS metadata periodically to a separate location to ensure quick recovery in case of a NameNode failure.

▪ The Standby NameNode uses these checkpoints to reduce the time needed for catching up with the Active NameNode after a failover.

▪ Checkpointing can be configured to occur at regular intervals, ensuring that the system can recover the HDFS metadata quickly without having to process all edit logs since the last checkpoint. By default, checkpointing is set to occur every hour.

☑ By employing Hadoop High Availability, using a Quorum Journal Manager, and enabling periodic checkpointing, Hadoop provides a robust mechanism to manage NameNode failures and ensure continuous availability and data integrity in the HDFS.

▪ It is essential to configure these features properly to achieve a highly available Hadoop cluster with minimal downtime.