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https://issues.apache.org/jira/browse/HBASE-21991?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16786224#comment-16786224
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Sakthi commented on HBASE-21991:
--------------------------------
Oh yes! Thanks [~xucang], Somehow I overlooked that it's a concurrentHashMap,
now, I can remove the synchronization. I still think there could be data
consistency problems as we are maintaining 2 different data members to
represent the state of the class. i.e. (requestsMap & registry). At any point
of time we either want values to be put/registered in both, or removed from
both. I feel operations such as below should be done by acquiring a lock to
make the 2 operations atomic. What do you think?
{code:java}
...
registry.meter(requestMeter);
requestsMap.put(requestMeter, registry.get(requestMeter));
..
requestsMap.remove(meter);
registry.remove(meter);
...
{code}
> Fix MetaMetrics issues - [Race condition, Faulty remove logic], few
> improvements
> --------------------------------------------------------------------------------
>
> Key: HBASE-21991
> URL: https://issues.apache.org/jira/browse/HBASE-21991
> Project: HBase
> Issue Type: Bug
> Components: Coprocessors, metrics
> Reporter: Sakthi
> Assignee: Sakthi
> Priority: Major
> Attachments: hbase-21991.master.001.patch
>
>
> Here is a list of the issues related to the MetaMetrics implementation:
> +*Bugs*+:
> # [_Lossy counting for top-k_] *Faulty remove logic of non-eligible meters*:
> Under certain conditions, we might end up storing/exposing all the meters
> rather than top-k-ish
> # MetaMetrics can throw NPE resulting in aborting of the RS because of a
> *Race Condition*.
> +*Improvements*+:
> # With high number of regions in the cluster, exposure of metrics for each
> region blows up the JMX from ~140 Kbs to 100+ Mbs depending on the number of
> regions. It's better to use *lossy counting to maintain top-k for region
> metrics* as well.
> # As the lossy meters do not represent actual counts, I think, it'll be
> better to *rename the meters to include "lossy" in the name*. It would be
> more informative while monitoring the metrics and there would be less
> confusion regarding actual counts to lossy counts.
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