Advanced topics

For readers who feel they have a good grasp of HBase fundamentals at this point, we will now cover advanced topics such as high availability, coprocessors, and SQL over HBase.

HBase high availability

In any enterprise looking to build mission-critical applications on top of HBase, the main questions on everybody's minds are Is the database reliable? What if it goes down? Under what conditions does it fail? How long will it take for the system to be functional again? Will there be lingering effects?

Let's try and understand each piece of this puzzle. As we've discussed, HBase favors strong consistency, and consequently makes a single RegionServer responsible for all reads and writes for a given key. When that RegionServer goes down, we lose access to the data stored within it and are unable to perform reads and writes with that data. However, since the underlying data is stored on HDFS, the loss of access is only temporary. Once the regions are reassigned to a different RegionServer...