Github user tison1 commented on the issue:
https://github.com/apache/flink/pull/6370
but the original `ensureConstraints` is wired. For example it calls
`ensureCapacity` twice and the only code path is from `ExecutionJobVertex`
construct `ExecutionVertex` which calls `ensureConstraints` from `0` to `N`,
which we gain little goodies from `ensureCapacity`. and so on.---
