provide "red flags" JMX instrumentation
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Key: CASSANDRA-3670
URL: https://issues.apache.org/jira/browse/CASSANDRA-3670
Project: Cassandra
Issue Type: Improvement
Reporter: Peter Schuller
Assignee: Peter Schuller
Priority: Minor
As discussed in CASSANDRA-3641, it would be nice to expose through JMX certain
information which is almost without exception indicative of something being
wrong with the node or cluster.
In the CASSANDRA-3641 case, it was the detection of corrupt counter shards.
Other examples include:
* Number of times the selection of files to compact was adjusted due to disk
space heuristics
* Number of times compaction has failed
* Any I/O error reading from or writing to disk (the work here is collecting,
not exposing, so maybe not in an initial version)
* Any data skipped due to checksum mismatches (when checksumming is being
used); e.g., "number of skips".
* Any arbitrary exception at least in certain code paths (compaction, scrub,
cleanup for starters)
Probably other things.
The motivation is that if we have clear and obvious indications that something
truly is wrong, it seems suboptimal to just leave that information in the log
somewhere, for someone to discover later when something else broke as a result
and a human investigates. You might argue that one should use non-trivial log
analysis to detect these things, but I highly doubt a lot of people do this and
it seems very wasteful to require that in comparison to just providing the
MBean.
It is important to note that the *lack* of a certain problem being advertised
in this MBean is not supposed to be indicative of a *lack* of a problem.
Rather, the point is that to the extent we can easily do so, it is nice to have
a clear method of communicating to monitoring systems where there *is* a clear
indication of something being wrong.
The main part of this ticket is not to cover everything under the sun, but
rather to reach agreement on adding an MBean where these types of indicators
can be collected. Individual counters can then be added over time as one thinks
of them.
I propose:
* Create an org.apache.cassandra.db.RedFlags MBean
* Populate with a few things to begin with.
I'll submit the patch if there is agreement.
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