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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2357) Add read-only region replicas (slaves) for availability and fast region recovery
Date Sat, 27 Mar 2010 00:33:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2357?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12850426#action_12850426

Andrew Purtell commented on HBASE-2357:

Stream edits with no freshness guarantee or use ZAB or Paxos over small (N=3) cliques? The
latter can do away with the WAL as an option or the leader can maintain the WAL as part of
the write transaction. This would still allow (a) and (b) but strengthen the consistency of
both. It's not clear if there would be a significant write penalty beyond what we already
take with durable WAL (hflush), especially if the WAL is only used if all members of a clique
fail, so the consensus protocol and hflush can happen in parallel. Crazy idea? 

> Add read-only region replicas (slaves) for availability and fast region recovery
> --------------------------------------------------------------------------------
>                 Key: HBASE-2357
>                 URL: https://issues.apache.org/jira/browse/HBASE-2357
>             Project: Hadoop HBase
>          Issue Type: New Feature
>          Components: master, regionserver
>            Reporter: Todd Lipcon
> 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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