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HBase NoSQL Interview Preparation (Q&A)



Question: Which data type is used to store the data in HBase table column.

Answer: Byte Array, Put p = new Put(Bytes.toBytes("John Smith")); All the data in the HBase is stored as raw byte Array (10101010). Now the put instance is created which can be inserted in the HBase users table. © HadoopExam Leaning Resource


Question: To locate the HBase data cell which three co-ordinate is used ?

Answer : HBase uses the coordinates to locate a piece of data within a table. The RowKey is the first coordinate. Following three co-ordinates define the location of the cell. : RowKey : Column Family (Group of columns) : Column Qualifier (Name of the columns or column itself e.g. Name, Email, Address) Co-ordinates for the John Smith Name Cell. ["John Smith userID", “info�, “name�]


Question: When you persist the data in HBase Row, In which tow places HBase writes the data to make sure the durability.

Answer : HBase receives the command and persists the change, or throws an exception if the write fails. When a write is made, by default, it goes into two places: a. the write-ahead log (WAL), also referred to as the HLog b. and the MemStore The default behavior of HBase recording the write in both places is in order to maintain data durability. Only after the change is written to and confirmed in both places is the write considered complete.


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. (The size of the MemStore is defined by the system-wide property in hbase-site.xml called hbase.hregion.memstore.flush.size)

Related Questions


Question: BlcokSize is configured on which level ?

Question: If your requirement is to read the data randomly from HBase User table. Then what would be your preference to keep blcok size.

Question: What is a block, in a BlockCache ?

Question: While reading the data from HBase, from which three places data will be reconciled before returning the value ?

Question: Once you delete the data in HBase, when exactly they are physically removed ?

Question: Please describe minor compaction

Question: Please describe major compactation ?

Question: What is tombstone record ?