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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-2357) Coprocessors: Add read-only region replicas (slaves) for availability and fast region recovery
Date Mon, 13 Jun 2011 18:56:52 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2357?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13048710#comment-13048710

Andrew Purtell commented on HBASE-2357:

CP Endpoints operate over HBase RPC.

bq. Sounds like the basic design is there are N slaves that connect to one master using a
socket based protocol.  There will be a socket connection open per-region per slave.

That is not how HBase RPC works. One connection between the endpoints (in this case regionserver
and regionserver) is established upon demand, reaped when idle too long, and multiplexed over
in the meantime.

bq. The Coprocessor will place edits into a per region queue

And spill the queues under heap pressure presumably. Or give up on a too laggy slave and have
it killed to avoid blowing out heap in the alternative. 

bq. Or should it function in the HMaster?

No we need to think of the HMaster as always on the verge of going away to be supplanted by
ZooKeeper mediated distributed actions.

> Coprocessors: Add read-only region replicas (slaves) for availability and fast region
> ----------------------------------------------------------------------------------------------
>                 Key: HBASE-2357
>                 URL: https://issues.apache.org/jira/browse/HBASE-2357
>             Project: HBase
>          Issue Type: Sub-task
>          Components: master, regionserver
>            Reporter: Todd Lipcon
>            Assignee: Andrew Purtell
> I dont plan on working on this in the short term, but the idea is to extend region ownership
to have two modes. Each region has one primary region server and N slave region servers. The
slaves would follow the master (probably by streaming the relevant HLog entries directly from
it) and be able to serve stale reads. The benefit is twofold: (a) provides the ability to
spread read load, (b) enables very fast region failover/rebalance since the memstore is already
nearly up to date on the slave RS.

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