We have been observed some occurrences of huge delay from file output committer V1, where file output committer V2 is not an option.
While the root cause should have investigated on our side, there's another issue that there's insufficient information to debug. Most likely the huge delay comes from mergePaths, but the class only provides the "debug" log message to log the call itself with parameters, nothing else. mergePaths has been called recursively which is harder to trace how much latency specific directory takes to merge.
It would be nice and not intrusive to add latency info in mergePath, so that we can see how much latency specific directory takes to merge, only when debug log is enabled.
(Ideally it'd be nice if we can log warn message when the call takes huge time to process, but I don't have the proper threshold for the "huge time", so I'd avoid dealing with it altogether here.)