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HBase Interview Questions

Q1. Can you create HBase table without assigning column family. © www.HadoopExam.com

Ans : No, Column family also impact how the data should be stored physically in the HDFS file system, hence there is a mandate that you should always have at least one column family. We can also alter the column families once the table is created. 

Q2. In which file the default configuration of HBase is stored. © www.HadoopExam.com

Ans : hbase-site.xml


Q3. What is the RowKey.

      Ans:   Every row in an HBase table has a unique identifier called its rowkey (Which is equivalent to Primary key in RDBMS, which would be distinct throughout the table). Every interaction you are going to do in database will start with the RowKey only. © www.Hadoop Exam.com

Q4. Please specify the command (Java API Class) which you will be using to interact with HBase table.

Ans: Get, Put, Delete, Scan, and Increment

Q5. Which data type is used to store the data in HBase table column.
Ans: 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

Q6. To locate the HBase data cell which three co-ordinate is used ?
Ans : 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.
1.    RowKey
2.    Column Family (Group of columns)
3.    Column Qualifier (Name of the columns or column itself e.g. Name, Email, Address) © HadoopExam Leaning Resource
Co-ordinates for the John Smith Name Cell.
["John Smith userID", “info”, “name”]

Q7. When you persist the data in HBase Row, In which tow places HBase writes the data to make sure the durability.
Ans : 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. © HadoopExam Leaning Resource

Q8. What is MemStore ?
Ans : 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. © HadoopExam Leaning Resource
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)

Q9. What is HFile ?
Ans : The HFile is the underlying storage format for HBase.
HFiles belong to a column family and a column family can have multiple HFiles.
But a single HFile can’t have data for multiple column families. © HadoopExam.com Leaning Resource

Q10. How HBase Handles the write failure.
Ans: Failures are common in large distributed systems, and HBase is no exception.
Imagine that the server hosting a MemStore that has not yet been flushed crashes. You’ll lose the data that was in memory but not yet persisted. HBase safeguards against that by writing to the WAL before the write completes. Every server that’s part of the.
HBase cluster keeps a WAL to record changes as they happen. The WAL is a file on the underlying file system. A write isn’t considered successful until the new WAL entry is successfully written. This guarantee makes HBase as durable as the file system backing it. Most of the time, HBase is backed by the Hadoop Distributed Filesystem (HDFS). If HBase goes down, the data that was not yet flushed from the MemStore to the HFile can be recovered by replaying the WAL. © Hado opE x a m

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