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Learning Hbase

You're reading from   Learning Hbase Learn the fundamentals of HBase administration and development with the help of real-time scenarios

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Product type Paperback
Published in Nov 2014
Publisher
ISBN-13 9781783985944
Length 326 pages
Edition 1st Edition
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Author (1):
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Shashwat Shriparv Shashwat Shriparv
Author Profile Icon Shashwat Shriparv
Shashwat Shriparv
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Table of Contents (12) Chapters Close

Preface 1. Understanding the HBase Ecosystem FREE CHAPTER 2. Let's Begin with HBase 3. Let's Start Building It 4. Optimizing the HBase/Hadoop Cluster 5. The Storage, Structure Layout, and Data Model of HBase 6. HBase Cluster Maintenance and Troubleshooting 7. Scripting in HBase 8. Coding HBase in Java 9. Advance Coding in Java for HBase 10. HBase Use Cases Index

Reading and writing cycle

Now, let's see how the read-and-write operation takes place in HBase diagrammatically:

Reading and writing cycle

Let's discuss and understand how the read-and-write operation takes place in and from HBase tables. In HBase, the client does not write data to HFile directly; it is first written to WAL and then to HBase MemStore, which is shared by an HStore in the main memory and then flushed to HFile later. Refer to the following figure:

Reading and writing cycle

Write-Ahead Logs

Write-Ahead Logs facilitate the data reliability and reside on HDFS; each RegionServer hosts a single WAL. In the case of a RegionServer crash where MemStore is not flushed, WAL is used to restore the data to a new RegionServer. So, only once data is written successfully to WAL and MemStore, the write operation is said to be successful.

MemStore

MemStore acts as an in-memory write buffer with a default size of 64 MB. Once data in MemStore reaches the threshold (which is by default 40 percent of the heap size or 64 MB), it is flushed...

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