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From "Enis Soztutar (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10498) Add new APIs to load balancer interface
Date Wed, 12 Feb 2014 01:15:25 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10498?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13898603#comment-13898603
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Enis Soztutar commented on HBASE-10498:
---------------------------------------

bq. Can you not add a new attribute for the Stochastic LB to consider – colocation – and
weight it above others rather than add API?
This is kind of the opposite of what we do for not co-locating the region replicas. The patch
at HBASE-10351 adds "soft" constraints for ensuring that the replicas are not co-located.
I highly suggest taking a look there. However, for secondary indexing, co-locating regions
should be a "hard constraint" I imagine. 

Still it should be possible to implement hard constraints like co-location inside the core
LB's, but implement the logic of deciding which regions to co-locate as a pluggable layer.


> Add new APIs to load balancer interface
> ---------------------------------------
>
>                 Key: HBASE-10498
>                 URL: https://issues.apache.org/jira/browse/HBASE-10498
>             Project: HBase
>          Issue Type: Improvement
>          Components: Balancer
>            Reporter: rajeshbabu
>            Assignee: rajeshbabu
>             Fix For: 0.98.1, 0.99.0
>
>
> If a custom load balancer required to maintain region and corresponding server locations,
> we can capture this information when we run any balancer algorithm before assignment(like
random,retain).
> But during master startup we will not call any balancer algorithm if a region already
assinged
> During split also we open child regions first in RS and then notify to master through
zookeeper. 
> So split regions information cannot be captured into balancer.
> Since balancer has access to master we can get the information from online regions or
region plan data structures in AM.
> But some use cases we cannot relay on this information(mainly to maintain colocation
of two tables regions). 
> So it's better to add some APIs to load balancer to notify balancer when *region is online
or offline*.
> These APIs helps a lot to maintain *regions colocation through custom load balancer*
which is very important in secondary indexing. 



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