Github user zentol commented on the issue:
https://github.com/apache/flink/pull/4647
@uce The checkstyle didn't catch it since the `runtime/executiongraph`
package isn't covered by checkstyle.
The flag will not fulfill the intended purpose after #4472 since the
fetched metrics will be inserted one by one and not atomically in batches
(neither as a whole nor by job/task/operator). The same issue applies to the
current master since `MutableIOMetric` doesn't synchronize on the metric store.
For the flag to properly work you will have to verify that every single
metric that you access from the store is not null. If any metric is null the
update isn't complete and you send back -1.
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