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From "Enis Soztutar (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-10070) HBase read high-availability using eventually consistent region replicas
Date Tue, 03 Dec 2013 00:46:35 GMT
Enis Soztutar created HBASE-10070:
-------------------------------------

             Summary: HBase read high-availability using eventually consistent region replicas
                 Key: HBASE-10070
                 URL: https://issues.apache.org/jira/browse/HBASE-10070
             Project: HBase
          Issue Type: New Feature
            Reporter: Enis Soztutar
            Assignee: Enis Soztutar


In the present HBase architecture, it is hard, probably impossible, to satisfy constraints
like 99th percentile of the reads will be served under 10 ms. One of the major factors that
affects this is the MTTR for regions. There are three phases in the MTTR process - detection,
assignment, and recovery. Of these, the detection is usually the longest and is presently
in the order of 20-30 seconds. During this time, the clients would not be able to read the
region data.

However, some clients will be better served if regions will be available for reads during
recovery for doing eventually consistent reads. This will help with satisfying low latency
guarantees for some class of applications which can work with stale reads.

For improving read availability, we propose a replicated read-only region serving design,
also referred as secondary regions, or region shadows. Extending current model of a region
being opened for reads and writes in a single region server, the region will be also opened
for reading in region servers. The region server which hosts the region for reads and writes
(as in current case) will be declared as PRIMARY, while 0 or more region servers might be
hosting the region as SECONDARY. There may be more than one secondary (replica count >
2).

Will attach a design doc shortly which contains most of the details and some thoughts about
development approaches. Reviews are more than welcome. 

We also have a proof of concept patch, which includes the master and regions server side of
changes. Client side changes will be coming soon as well. 






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