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From "cuijianwei (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12770) Don't transfer all the queued hlogs of a dead server to the same alive server
Date Wed, 31 Dec 2014 04:10:13 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12770?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14261886#comment-14261886
] 

cuijianwei commented on HBASE-12770:
------------------------------------

Thanks for your concern. I agree that it will be helpful to balance replication loads among
region servers if we know queue depths of peers. The coordinator could be the master, or on
the other hand, I am not sure whether we can have a method to conduct stable balanced replication
loads for peers without the central coordinator. As an optional way, the RS could know the
total queued hlog count if every RS report their queue depths, then each RS could compute
the average replication load based on the current alive RS count when transferring queues,
this might help the RS to better decide whether to transfer a queue. I will work on the detail
to have a try.

> Don't transfer all the queued hlogs of a dead server to the same alive server
> -----------------------------------------------------------------------------
>
>                 Key: HBASE-12770
>                 URL: https://issues.apache.org/jira/browse/HBASE-12770
>             Project: HBase
>          Issue Type: Improvement
>          Components: Replication
>            Reporter: cuijianwei
>            Priority: Minor
>
> When a region server is down(or the cluster restart), all the hlog queues will be transferred
by the same alive region server. In a shared cluster, we might create several peers replicating
data to different peer clusters. There might be lots of hlogs queued for these peers caused
by several reasons, such as some peers might be disabled, or errors from peer cluster might
prevent the replication, or the replication sources may fail to read some hlog because of
hdfs problem. Then, if the server is down or restarted, another alive server will take all
the replication jobs of the dead server, this might bring a big pressure to resources(network/disk
read) of the alive server and also is not fast enough to replicate the queued hlogs. And if
the alive server is down, all the replication jobs including that takes from other dead servers
will once again be totally transferred to another alive server, this might cause a server
have a large number of queued hlogs(in our shared cluster, we find one server might have thousands
of queued hlogs for replication). As an optional way, is it reasonable that the alive server
only transfer one peer's hlogs from the dead server one time? Then, other alive region servers
might have the opportunity to transfer the hlogs of rest peers. This may also help the queued
hlogs be processed more fast. Any discussion is welcome.



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