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https://issues.apache.org/jira/browse/HBASE-10070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14006238#comment-14006238
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Enis Soztutar commented on HBASE-10070:
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bq. But we consider that being able to define consistency level per-operation
is mandatory, right?
Yes.
bq. deploy pluggable policy at client side which which decide on RPC requests,
this policy would be used globally for all requests as default
Right now there is no alternate implementation for normal RPCs, and only 1
model for TIMELINE RPCs. When we have alternate implementations, we can make it
pluggable (and configurable per operation).
bq. current timeline consistency model doesn't assume quorums for write, so I
think it makes sense to add QUORUM_STRONG in enum.
I don't like adding this now. Once we have a corresponding implementation for
the proposed quorum write we can add it to the enum later.
> HBase read high-availability using timeline-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
> Attachments: HighAvailabilityDesignforreadsApachedoc.pdf
>
>
> 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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