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Secondary namenode is responsible for writing editlogs of NameNode in file called fSimage in HDFS. After which the edit logs are cleared. This activity is done periodically which helps minimizing the size of edit log files(since changes are flushed to fsimage on secondary namenode).
The Checkpoint Node fetches periodically fsimage and edits from the NameNode and merges them.
The resulting state is called checkpoint. After this is uploads the result to the NameNode.The main difference between Secondary and Checkpoint namenode is secondary namenode does not upload the merged Fsimage with editlogs to active namenode
where as the checkpoint node uplods the merged new image back to active Namenode.
So the NameNode need to fetch the state from the Secondary NameNode -
Checkpointing in HDFS plays a vital role . Checkpointing is basically a process which involves merging the fsimage along with the latest edit log and creating a new fsimage for the namenode to possess the latest configured metadata of HDFS namespace .
Now one can say this task can be performed by a Secondary Namenode or a Standby Namenode as well .
Well here lies a small difference:-
The Secondary namenode performs the mapping of the fsimage and the edit log transactions periodically stores them in a shared storage location in case of HA enabled HDFS Cluster.
But in case of a Checkpoint node , it has the ability to transfer the latest built fsimage to the Active NameNode via HTTP Get call .
This is the prime advantage of a Checkpoint node over a secondary namenode .
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main difference between secondary name node and checkpoint node is how these will maintain and modifies the fs imapege
file.
fsimage: is nothing but which stores the file system directories and mapping of blocks to files and file system directories.Secondary name node is not only for the backup if name node but it is used for maintaining the fs image file and log files
periodically and maintains the log files withing a limit.Check point node is used to take the fs image file from the active name node and mergers them locally and uploads
the new image back to the active name node.checkpoint will have upload feature where a secondary name node don’t have.
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