Anoop Sam John created HBASE-20003:

             Summary: WALLess HBase on Persistent Memory
                 Key: HBASE-20003
             Project: HBase
          Issue Type: New Feature
            Reporter: Anoop Sam John
            Assignee: Anoop Sam John

This JIRA aims to make use of persistent memory (pmem) technologies in HBase. 
One such usage is to make the Memstore to reside on pmem. Making a persistent 
memstore would remove the need for WAL and paves way for a WALLess HBase. 

The existing region replica feature could be used here and ensure the data 
written to memstores are synchronously replicated to the replicas and ensure 
strong consistency of the data. (pipeline model)

Advantages :
-Data Availability : Since the data across replicas are consistent 
(synchronously written) our data is always 100 % available.
-Lower MTTR : It becomes easier/faster to switch over to the replicas on a 
primary region failure as there is no WAL replay involved. Building the 
memstore map data also is much faster than reading the WAL and replaying the 
-Possibility of bigger memstores : These pmems are designed to have more memory 
than DRAMs so it would also enable us to have bigger sized memstores which 
leads to lesser flushes/compaction IO. 
-Removes the dependency of HDFS on the write path

Initial PoC has been designed and developed. Testing is underway and we would 
publish the PoC results along with the design doc sooner. The PoC doc will talk 
about the design decisions, the libraries considered to work with these pmem 
devices, pros and cons of those libraries and the performance results.

Note : Next gen memory technologies using 3DXPoint gives persistent memory 
feature. Such memory DIMMs are soon to appear in the market. The PoC is done 
around Intel's ApachePass (AEP)

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