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https://issues.apache.org/jira/browse/HBASE-25185?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17214341#comment-17214341
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Michael Stack commented on HBASE-25185:
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bq. The comment of RegionPlacementMaintainer says it is only partially
implemented and is marked as IA.Private, so maybe we can just remove it?
Comment was added in 2014 by HBASE-12471; I may not have known what I was
talking about.
Looking at hbase-balancer issue (HBASE-23933 Separate a hbase-balancer or
hbase-assignment module), the demarcation as to what went goes into
hbase-balancer and what stays in hbase-server looks arbitrary. For example, the
StochasticBalancer was left in hbase-server. This latter makes sense because it
needs access to info the Master has to operate which makes sense; I'd think a
smart balancer would need access to what the Master knows to work well.
The FN classes moved to hbase-balancer include classes that are buidling for
themselves info the Master has and then they want to write the hbase-meta table
w/ what they've figured. The likes of SnapshotOfRegionAssignmentFromMeta looks
to build for itself datastructures the Master has internally by doing its own
hbase:meta scan. FN needs updating/refactoring at least.
Here is suggested patch that moves MTA to hbase-server from hbase-balancer,
adds an hbase-tool to host the FN placement tool (and to which I'll move other
tools in a follow-on most of which live in hbase-server), and then moves some
of the balancer FN stuff around to undo balancer dependencies on MTA.
> Remove the usage of MetaTableAccessor in hbase-balancer
> -------------------------------------------------------
>
> Key: HBASE-25185
> URL: https://issues.apache.org/jira/browse/HBASE-25185
> Project: HBase
> Issue Type: Sub-task
> Components: Balancer, meta
> Reporter: Duo Zhang
> Priority: Major
>
> Let's try to find a way to move MTA to hbase-server. Putting it in
> hbase-balancer is a bit weird (Why is the MetaTableAccessor in the balancer
> module?).
> MetaTableAccessor (MTA) is in hbase-balancer because the favored nodes (FN)
> feature wants to write to meta.
> The FN feature (HBASE-7932 which arrived in hbase-0.96.0) I believe is
> unused. The idea of maintaining locality across a crash is a good one but
> having to enable a different balancer to default to enable FN operation has
> made it so the feature has been let rot. HBASE-21014 makes an appeal for
> integrating FN into the default stochastic balancer. HBASE-15531 is an old
> effort that actually tried to integrate FN into stochastic balancer but
> stalled out.
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