Kurt, 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 java.util.concurrent.ThreadPoolExecutor. 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 <k...@instaclustr.com>: > 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 > <https://issues.apache.org/jira/browse/CASSANDRA-4009>, which also has no > useful info. > > On 27 October 2017 at 13:48, Lucas Benevides <lu...@maurobenevides.com.br> > 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 (http://cassandra.apache.org/d >> 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 metrics.CompactionMetrics.java): >> 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 >> >> >