Defining the Schema - HBase Essentials - page 24

The HTable class is not thread-safe as concurrent modiications are not safe. Hence,
a single instance of HTable for each thread should be used in any application.
For multiple HTable instances with the same coniguration reference, the same
underlying HConnection instance can be used.
Creating HTable instances also comes at a cost. Creating an HTable instance is a slow
process as the creation of each HTable instance involves the scanning of the .META
table to check whether the table actually exists, which makes the operation very
costly. Hence, it is not recommended that you use a new HTable instance for each
request where the number of concurrent requests are very high.
Whenever there is a requirement of multiple instances of HTable , consider using
the HTablePool class. The following constructor can be used to create an instance
of HTablePool :
HTablePool()
HTablePool(Configuration config, int maxSize)
HTablePool(Configuration config, int maxSize,
HTableInterfaceFactory tableFactory)
The HTablePool class creates a pool with the HTable class instances with the
coniguration object, and setting the maxSize parameter deining the HTable
instances to count a pool. Here is the code for getting the HTable instance from
HTablePool :
HTableInterface usersTable = pool.getTable("Costumers");
CRUD operations
A rowkey primarily represents each row uniquely in the HBase table, whereas other
keys such as column family, timestamp, and so on are used to locate a piece of data
in an HBase table. The HBase API provides the following methods to support the
CRUD operations:
• Put
• Get
• Delete
• Scan
• Increment
Let's discuss the irst three methods in detail and the rest will be covered in the
coming chapters.