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)