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https://issues.apache.org/jira/browse/HBASE-10070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14005082#comment-14005082
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stack commented on HBASE-10070:
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bq. and hooking into Get and Scan, and defining several possible internal
strategies on how to send RPCs based on that ("primary timeout", "parallel",
"parallel with delay" ) may be we can define pluggable strategy on how to
execute RPCs? Similar to HDFS FailoverProxyProvider, which can be defined in
the client's config.
[~mantonov] So, rather than have the client ask for level of 'consistency' in
the API, instead, the replica interaction would be set on client construction
dependent on the plugin supplied?
In the API at the moment we have STRONG and TIMELINE (What happens if I ask for
TIMELINE and cluster is not deployed with read replicas? Ignored?). If we
were to add QUORUM_STRONG, are we thinking that a client should be able to
choose amongst these options? Will that fly? At the moment, as noted, we have
amended Get and Scan. We'll have to amend all ops if we follow the path of
HBASE-10513?
How hard to evolve from HBASE-10513 to [~mantonov] suggestion?
> 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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