Stefan Egli created OAK-2635:
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Summary: TimeSeriesMax's frequent 'drops to 0'
Key: OAK-2635
URL: https://issues.apache.org/jira/browse/OAK-2635
Project: Jackrabbit Oak
Issue Type: Bug
Components: core
Affects Versions: 1.0.12
Reporter: Stefan Egli
The current implementation of TimeSeriesMax - which is what is backing eg the
very important 'ObservationQueueMaxLength' statistics - has a very infamous
behavior: it does very frequent, intermittent 'jumps back to 0'. This even
though the queue-lengths are still at the previous highs, as can often be seen
with subsequent measurements (which eg are still showing there are 1000 events
in the observation queue).
The reason seems to be that
* the value is increased via {{TimeSeriesMax.recordValue()}} during a 1 second
interval
* reset to 0 via {{TimeSeriesMax<init>.run()}} every second
So basically, every second the counter is reset, then during 1 second if any
call to {{recordValue()}} happens, it is increased.
This in my view is rather unfortunate - as it can result in mentioned 'jumpy-0'
behavior, but it can also jump to values in between if the largest queue does
not reports its length during 1 second.
It sounds a bit like this was done this way intentionally? (perhaps to make it
as inexpensive as possible) or could this be fixed?
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