Enis Soztutar created HBASE-10070:
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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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