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From "Jesse Yates (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8925) [replication] Allow lazy RS to help overwhelmed RS
Date Thu, 11 Jul 2013 23:33:49 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8925?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13706450#comment-13706450

Jesse Yates commented on HBASE-8925:

Assuming they are on that machine, that's definitely the case. But a single RS failure could
cause a large massive queue backup (if that one is behind), in which case the files probably
aren't on that machine.
> [replication] Allow lazy RS to help overwhelmed RS
> --------------------------------------------------
>                 Key: HBASE-8925
>                 URL: https://issues.apache.org/jira/browse/HBASE-8925
>             Project: HBase
>          Issue Type: Improvement
>    Affects Versions: 0.98.0, 0.95.2, 0.94.10
>            Reporter: Jesse Yates
> Sometimes in usual course of things, one of the regionservers gets waaaaay behind replicating
its queue; easily build-ups of 40-50 files over just a day (running YCSB at the same time).
However, this is just for a single RS - others don't have anything to replicate. We can manually
get around this by moving the region load away from the overloaded server (and get smarter
about this by writing our own load balancer). However, moving regions around just to catch
up the replication seems a bit heavyweight.
> From this thread on the dev list: http://mail-archives.apache.org/mod_mbox/hbase-dev/201211.mbox/%3CCAFLnt_qj1stL=vre5AbWqawpkwKG7LDebwCyhddkBQvX4UpaAg@mail.gmail.com%3E
> it seems like we can already get out-of-order updates for a table on the target cluster.
Given this is already the behavior (though not common), we could allow a 'lazy' RS to have
a secondary log to replicate when it has time. 
> This adds a bit more complexity around who owns which log for replication, but could
dramatically increase throughput as you aren't bottle-necked by the single slow host.

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