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https://issues.apache.org/jira/browse/HBASE-4755?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Devaraj Das updated HBASE-4755:
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Priority: Critical (was: Major)
> HBase based block placement in DFS
> ----------------------------------
>
> Key: HBASE-4755
> URL: https://issues.apache.org/jira/browse/HBASE-4755
> Project: HBase
> Issue Type: New Feature
> Affects Versions: 0.94.0
> Reporter: Karthik Ranganathan
> Assignee: Christopher Gist
> Priority: Critical
> Attachments: 4755-wip-1.patch
>
>
> The feature as is only useful for HBase clusters that care about data
> locality on regionservers, but this feature can also enable a lot of nice
> features down the road.
> The basic idea is as follows: instead of letting HDFS determine where to
> replicate data (r=3) by place blocks on various regions, it is better to let
> HBase do so by providing hints to HDFS through the DFS client. That way
> instead of replicating data at a blocks level, we can replicate data at a
> per-region level (each region owned by a promary, a secondary and a tertiary
> regionserver). This is better for 2 things:
> - Can make region failover faster on clusters which benefit from data affinity
> - On large clusters with random block placement policy, this helps reduce the
> probability of data loss
> The algo is as follows:
> - Each region in META will have 3 columns which are the preferred
> regionservers for that region (primary, secondary and tertiary)
> - Preferred assignment can be controlled by a config knob
> - Upon cluster start, HMaster will enter a mapping from each region to 3
> regionservers (random hash, could use current locality, etc)
> - The load balancer would assign out regions preferring region assignments to
> primary over secondary over tertiary over any other node
> - Periodically (say weekly, configurable) the HMaster would run a locality
> checked and make sure the map it has for region to regionservers is optimal.
> Down the road, this can be enhanced to control region placement in the
> following cases:
> - Mixed hardware SKU where some regionservers can hold fewer regions
> - Load balancing across tables where we dont want multiple regions of a table
> to get assigned to the same regionservers
> - Multi-tenancy, where we can restrict the assignment of the regions of some
> table to a subset of regionservers, so an abusive app cannot take down the
> whole HBase cluster.
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