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https://issues.apache.org/jira/browse/HBASE-10070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14005073#comment-14005073
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Andrew Purtell commented on HBASE-10070:
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bq. Can I ask what definition of timeline consistency are we using here?
I believe the Yahoo PNUTS paper is where many have first heard the term
'timeline consistency'. Daniel Abadi summarizes it at
http://dbmsmusings.blogspot.com/2010/04/problems-with-cap-and-yahoos-little.html
as "where replicas may not be consistent with each other but updates are
guaranteed to be applied in the same order at all replicas", which I think is
very concise.
If we claim this about HBASE-10070, is that accurate? (I think yes.)
If so, the documentation committed on HBASE-10513 doesn't summarize the term as
cleanly in my opinion. Might be good to update the lead in to the timeline
consistency part of the doc.
> 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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