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From Lucas Benevides <>
Subject Re: Cassandra Compaction Metrics - CompletedTasks vs TotalCompactionCompleted
Date Mon, 30 Oct 2017 17:22:37 GMT

I apreciate your answer but I don't believe CompletedTasks count the
"validation compactions". These are compactions that occur from repair
operations. I am running tests on 10 cluster nodes in the same physical
rack, with Cassandra Stress Tool and I didn't make any Repair commands. The
tables only last for seven hours, so it is not reasonable that tens of
thousands of these validation compactions occur per node.

I tried to see the code and the CompletedTasks counter seems to be
populated by a method from the class
So I really don't know what it is but surely is not the amount of
Compaction Completed Tasks.

Thank you
Lucas Benevides


2017-10-30 8:05 GMT-02:00 kurt greaves <>:

> I believe (may be wrong) that CompletedTasks counts Validation compactions
> while TotalCompactionsCompleted does not. Considering a lot of validation
> compactions can be created every repair it might explain the difference.
> I'm not sure why they are named that way or work the way they do. There
> appears to be no documentation around this in the code (what a surprise)
> and looks like it was last touched in CASSANDRA-4009
> <>, which also has no
> useful info.
> On 27 October 2017 at 13:48, Lucas Benevides <>
> wrote:
>> Dear community,
>> I am studying the behaviour of the Cassandra
>> TimeWindowCompactionStragegy. To do so I am watching some metrics. Two of
>> these metrics are important: Compaction.CompletedTasks, a gauge, and the
>> TotalCompactionsCompleted, a Meter.
>> According to the documentation (
>> oc/latest/operating/metrics.html#table-metrics):
>> Completed Taks = Number of completed compactions since server [re]start.
>> TotalCompactionsCompleted = Throughput of completed compactions since
>> server [re]start.
>> As I realized, the TotalCompactionsCompleted, in the Meter object, has a
>> counter, which I supposed would be numerically close to the CompletedTasks
>> gauge. But they are very different, with the Completed Tasks being much
>> higher than the TotalCompactions Completed.
>> According to the code, in github (class
>> Completed Taks - Number of completed compactions since server [re]start
>> TotalCompactionsCompleted - Total number of compactions since server
>> [re]start
>> Can you help me and explain the difference between these two metrics, as
>> they seem to have very distinct values, with the Completed Tasks being
>> around 1000 times the value of the counter in TotalCompactionsCompleted.
>> Thanks in Advance,
>> Lucas Benevides

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