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https://issues.apache.org/jira/browse/HBASE-20003?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16374510#comment-16374510
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huaxiang sun commented on HBASE-20003:
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Currently, replica region is only for read, not for write, do we consider to 
promote replica region to "primary" in case of primary down?

Another point is region blowup. With 1 primary + 2 replicas, the cluster will 
have 3 * normal-user-regions.

> WALLess HBase on Persistent Memory
> ----------------------------------
>
>                 Key: HBASE-20003
>                 URL: https://issues.apache.org/jira/browse/HBASE-20003
>             Project: HBase
>          Issue Type: New Feature
>            Reporter: Anoop Sam John
>            Assignee: Anoop Sam John
>            Priority: Major
>
> 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 
> WAL.
> - 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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