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From "Phil Yang (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 Fri, 01 Jul 2016 11:00:16 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12770?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15358796#comment-15358796

Phil Yang commented on HBASE-12770:

Hi all
This is an old issue, I'm going to pick up [~cuijianwei]'s work. We can decrease the delay
of replication a lot by balancing the number of queues in each RS. I'll upload a new patch
whose logic may be a little different from Jianwei's. The basic idea is:

When we get event of RSRemoved, we can do a repeatable job (read the list of queues in dead
RS, and try to transfer a random queue) until the list is empty. Between the repeatable jobs
we should sleep several seconds to let other region servers move some queues (sleep shorter
if it doesn't claim any queue last time, sleep longer if it moved a queue, two fixed sleep
time here, no random). If we disable hbase.zookeeper.useMulti, the lock is still RS level
(different from Jianwei's patch for compatibility).

Although we may still can not balance the number of queues perfectly, I think it is much better
than now.

Any thoughts? Thanks.

> 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: Jianwei Cui
>            Assignee: Phil Yang
>            Priority: Minor
>         Attachments: HBASE-12770-trunk.patch
> 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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