BigData Interview Questions – Hbase

BigData Interview Questions – Hbase

Question: What are key components of Hbase?
Answer: Main components of Hbase :-
Hmaster
Zoopkeeper
Region Server

Other main components are :-
Memstore
Hfile
WAL

Question: What role does Zookeeper plays in Hbase?
Answer: HBase comes integrated with Zoo keeper. When I start HBase, Zoo keeper instance is also started. The reason is that the Zoo keeper helps us in keeping a track of all region servers that are there for HBase. Zoo keeper keeps track of how many region servers are there, which region servers are holding from which data node to which data node. It keeps track of smaller data sets where Hadoop is missing out. It decreases the overhead on top of Hadoop which keeps track of most of your Meta data. Hence HMaster gets the details of region servers by actually contacting Zoo keeper.

Question: What is MemStore ?
Answer: The MemStore is a write buffer where HBase accumulates data in memory before a permanent write.
Its contents are flushed to disk to form an HFile when the MemStore fills up.It doesn’t write to an existing HFile but instead forms a new file on every flush. There is one MemStore per column family.

Question: What is WAL ?
Answer: We cannot be sure that the data will be persistent throughout in Memstore. Assume that a particular datanode is down. Then the data that resides on that data node’s memory will be lost.
To overcome this problem, when the request comes from the master it written to WAL as well. WAL is nothing but Write Ahead Logs which resides on the HDFS, a permanent storage. Now we can make sure that even when if the data node is down the data will not be lost I.e. we have the copy of all the actions that you are supposed to do in the WAL.

Question: What are the two types of table design approach in Hbase?
Answer: They are − (i) Short and Wide (ii) Tall and Thin

Question: What are the two types of table design approach in Hbase?
Answer: They are − (i) Short and Wide (ii) Tall and Thin

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