somandal commented on code in PR #15517:
URL: https://github.com/apache/pinot/pull/15517#discussion_r2039903191
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pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/rebalance/TableRebalancer.java:
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@@ -431,6 +432,10 @@ private RebalanceResult doRebalance(TableConfig
tableConfig, RebalanceConfig reb
estimatedAverageSegmentSizeInBytes, allSegmentsFromIdealState,
segmentsToMonitor);
// Record the beginning of rebalance
+ // We emit this metric only when the rebalance does get to this code path,
i.e. excluding dry-run and downtime
+ if (_controllerMetrics != null) {
Review Comment:
For gauge you can track the total number of ongoing rebalances in an
AtomicInteger and use that to increment / decrement and set the gauge value
(you don't need to use the deprecated method). I did something similar for
`BaseSegmentOperationsThrottler`. I think for this purpose gauge is probably a
better fit.
what race condition are you worried about? can you elaborate?
I thought some more about how to count rebalances. I think if we want to
simplify and count all rebalances (even no-ops, downtime, dryRun) that is fine,
these are quick and the metric won't be high for too long.
Meters are more for measuring rate. I don't think we care about rate of
rebalances here, the absolute number is what is more useful. Can you do some
research on the behavior of Meters for decrementing them and whether that is
even a recommended pattern?
https://javadoc.io/doc/io.dropwizard.metrics/metrics-core/3.2.1/com/codahale/metrics/Meter.html
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