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From "Bryan Duxbury (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-55) [hbase] Improve Master region assignment function
Date Wed, 13 Feb 2008 03:26:07 GMT

    [ https://issues.apache.org/jira/browse/HBASE-55?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12568419#action_12568419
] 

Bryan Duxbury commented on HBASE-55:
------------------------------------

I think the tricky part of trying to incorporate update/read rate and memory usage is that
this could change very quickly, and if we are making balancing decisions based on this, we
could get really bad oscillations in assignments. 

Moreover, there's really no such thing as "too busy". Either it's less busy than average,
and it should take on new regions, or more busy than average, and regions should be taken
away. If all of the servers have equal load, but the average is "too high", then all you get
is poor performance. At no point does it make sense for a region server to "say no" to an
assignment, because in theory the master has decided that assignment is optimal for the known
factors. 

I think that calculating the load factor has to be simple, otherwise we can easily get caught
up trying to build a complicated load function that takes into account every factor the region
server can offer, but only provides a marginal improvement over simpler functions. 

Let's try a simple metric and see what happens. If it fails to give us decent distribution,
then we can go back to the drawing board.

As far as HBASE-70, I see that not so much as a way for us to monitor how much memory is in
use as for each region server to work best within the memory it has. Perhaps we also need
to be aware of the "swappiness" of a region server (how much of it's cache is being discarded
due to memory pressure), but that may be separate.

> [hbase] Improve Master region assignment function
> -------------------------------------------------
>
>                 Key: HBASE-55
>                 URL: https://issues.apache.org/jira/browse/HBASE-55
>             Project: Hadoop HBase
>          Issue Type: Improvement
>          Components: regionserver
>            Reporter: Bryan Duxbury
>             Fix For: 0.2.0
>
>
> We would like the master's region assignment function to take into account more factors
when choosing where to assign regions.
>  
> - More advanced accounting of load on regionserver - memory, # requests, etc
> - Don't deploy both daughter regions to the same regionserver
> - Assign regions where the underlying DFS blocks are hosted if possible
> Please add additional ideas in comments as they come up.

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