Quick Answer: What Happens If Secondary NameNode Fails?

What is Hadoop architecture?

The Hadoop architecture is a package of the file system, MapReduce engine and the HDFS (Hadoop Distributed File System).

The MapReduce engine can be MapReduce/MR1 or YARN/MR2.

A Hadoop cluster consists of a single master and multiple slave nodes..

What is the purpose of the secondary name node?

The secondary NameNode merges the fsimage and the edits log files periodically and keeps edits log size within a limit. It is usually run on a different machine than the primary NameNode since its memory requirements are on the same order as the primary NameNode.

What will happen if NameNode doesn’t have any data?

What happens to a NameNode that has no data? Answer:There does not exist any NameNode without data. If it is a NameNode then it should have some sort of data in it.

What is DataNode in Hadoop?

DataNode: DataNodes are the slave nodes in HDFS. Unlike NameNode, DataNode is a commodity hardware, that is, a non-expensive system which is not of high quality or high-availability. The DataNode is a block server that stores the data in the local file ext3 or ext4.

What is the difference between Hadoop 1 and Hadoop 2?

In Hadoop 1, there is HDFS which is used for storage and top of it, Map Reduce which works as Resource Management as well as Data Processing. … In Hadoop 2, there is again HDFS which is again used for storage and on the top of HDFS, there is YARN which works as Resource Management.

How do I disable secondary NameNode in Hadoop?

InstructionsExecute this command on all NodeManagers: su -l yarn -c “/usr/hdp/current/hadoop-yarn-nodemanager/sbin/yarn-daemon.sh stop nodemanager”Execute this command on the History Server host machine: su -l mapred -c “/usr/hdp/current/hadoop-mapreduce-historyserver/sbin/mr-jobhistory-daemon.sh stop historyserver”More items…

What is checkpointing in Hadoop?

Checkpointing is a process that takes an fsimage and edit log and compacts them into a new fsimage. This way, instead of replaying a potentially unbounded edit log, the NameNode can load the final in-memory state directly from the fsimage. This is a far more efficient operation and reduces NameNode startup time.

What was Hadoop named after?

What was Hadoop named after? Explanation: Doug Cutting, Hadoop creator, named the framework after his child’s stuffed toy elephant. Explanation: Apache Hadoop is an open-source software framework for distributed storage and distributed processing of Big Data on clusters of commodity hardware. 8.

What is the difference between a NameNode and a secondary NameNode?

Secondary namenode is just a helper for Namenode. It gets the edit logs from the namenode in regular intervals and applies to fsimage. Once it has new fsimage, it copies back to namenode. Namenode will use this fsimage for the next restart, which will reduce the startup time.

How does Hadoop work when a DataNode fails?

What happens if one of the Datanodes gets failed in HDFS? Namenode periodically receives a heartbeat and a Block report from each Datanode in the cluster. Every Datanode sends heartbeat message after every 3 seconds to Namenode.

Can you access cluster and data if NameNode is down?

So if Namenode is down (Master node), then the data remains as is in the cluster, BUT you will not be able to access it at all. Because, Name node holds the meta data of the data nodes. … So you can still access the data from other two nodes.

When a NameNode fails what action should be taken?

Whenever the active NameNode fails, the passive NameNode or the standby NameNode replaces the active NameNode, to ensure that the Hadoop cluster is never without a NameNode. The passive NameNode takes over the responsibility of the failed NameNode and keep the HDFS up and running.

What is Fsimage in Hadoop?

The entire file system namespace, including the mapping of blocks to files and file system properties, is stored in a file called the FsImage. The FsImage is stored as a file in the NameNode’s local file system too. The NameNode keeps an image of the entire file system namespace and file Blockmap in memory.

Is the secondary NameNode is the backup node?

No, Secondary NameNode is not a backup of NameNode. You can call it a helper of NameNode. NameNode is the master daemon which maintains and manages the DataNodes. It regularly receives a Heartbeat and a block report from all the DataNodes in the cluster to ensure that the DataNodes are live.

What if secondary NameNode fails?

If NameNode is failed, File System metadata can be recovered from the last saved FsImage on the Secondary NameNode but Secondary NameNode can’t take the primary NameNode’s functionality.

What is the purpose of secondary NameNode in Hadoop?

The main function of the Secondary namenode is to store the latest copy of the FsImage and the Edits Log files. How does it help? When the namenode is restarted , the latest copies of the Edits Log files are applied to the FsImage file in order to keep the HDFS metadata latest.

How does NameNode tackle DataNode failures and what will you do when NameNode is down?

This is how Namenode handles datanode failures. HDFS works in Master/Slave mode where NameNode act as a Master and DataNodes act as a Slave. NameNode periodically receives a Heartbeat and a Data Blocks report from each of the DataNodes in the cluster in an interval of specified time.

How does Hadoop MapReduce work?

A MapReduce job usually splits the input data-set into independent chunks which are processed by the map tasks in a completely parallel manner. The framework sorts the outputs of the maps, which are then input to the reduce tasks. Typically both the input and the output of the job are stored in a file-system.

What happens when a NameNode fails?

The single point of failure in Hadoop v1 is NameNode. If NameNode gets fail the whole Hadoop cluster will not work. Actually, there will not any data loss only the cluster work will be shut down, because NameNode is only the point of contact to all DataNodes and if the NameNode fails all communication will stop.

What happens when the NameNode on the Hadoop cluster goes down?

The NameNode is the centerpiece of an HDFS file system. It keeps the directory tree of all files in the file system, and tracks where across the cluster the file data is kept. … HDFS is not currently a High Availability system. When the NameNode goes down, the file system goes offline.

How can I recover my NameNode is down?

Recover Hadoop NameNode FailureStart the namenode in a different host with a empty dfs. name. dir.Point the dfs. name. … Use –importCheckpoint option while starting namenode after pointing fs. checkpoint. … Change the fs.default.name to the backup host name URI and restart the cluster with all the slave IP’s in slaves file.