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https://issues.apache.org/jira/browse/HBASE-24528?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17132660#comment-17132660
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Andrew Kyle Purtell commented on HBASE-24528:
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{quote}how we solve using workflow in HMaster vs RegionServer is where I am
stuck currently.
{quote}
At a high level, we factor out a single common framework for logging to an
in-memory ring buffer, the ring buffer impl, and RPC service supporting it.
Support allocation of one or more _named_ ring buffers. A ring buffer can
optionally also have write-behind persistence. The size of the ring buffer and
the persistence option and its configuration can be constructor parameters.
Make a builder API for added convenience. Put all of this into hbase-server.
Then, both the master and regionserver implementations can import the framework
and instantiate ring buffers with specific names. The regionserver has one
named "slow_log". The master has one named "balancer", or maybe
"balancer_plans".
Then, shell commands and UI widgets can use RPC for looking up a named ring
buffer and enumerating its contents (or its backing persistence) to show what
it must.
What is put into a ring buffer can be anything, but we presume it is some
protobuf encoded structure for ease of serialization and deserialization and
cross version compatibility.
> Improve balancer decision observability
> ---------------------------------------
>
> Key: HBASE-24528
> URL: https://issues.apache.org/jira/browse/HBASE-24528
> Project: HBase
> Issue Type: New Feature
> Components: Admin, Balancer, Operability, shell, UI
> Reporter: Andrew Kyle Purtell
> Priority: Major
>
> We provide detailed INFO and DEBUG level logging of balancer decision
> factors, outcome, and reassignment planning, as well as similarly detailed
> logging of the resulting assignment manager activity. However, an operator
> may need to perform online and interactive observation, debugging, or
> performance analysis of current balancer activity. Scraping and correlating
> the many log lines resulting from a balancer execution is labor intensive and
> has a lot of latency (order of ~minutes to acquire and index, order of
> ~minutes to correlate).
> The balancer should maintain a rolling window of history, e.g. the last 100
> region move plans, or last 1000 region move plans submitted to the assignment
> manager. This history should include decision factor details and weights and
> costs. The rsgroups balancer may be able to provide fairly simple decision
> factors, like for example "this table was reassigned to that regionserver
> group". The underlying or vanilla stochastic balancer on the other hand,
> after a walk over random assignment plans, will have considered a number of
> cost functions with various inputs (locality, load, etc.) and multipliers,
> including custom cost functions. We can devise an extensible class structure
> that represents explanations for balancer decisions, and for each region move
> plan that is actually submitted to the assignment manager, we can keep the
> explanations of all relevant decision factors alongside the other details of
> the assignment plan like the region name, and the source and destination
> regionservers.
> This history should be available via API for use by new shell commands and
> admin UI widgets.
> The new shell commands and UI widgets can unpack the representation of
> balancer decision components into human readable output.
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