Github user sihuazhou commented on the issue:
https://github.com/apache/flink/pull/5465
I think maybe a best way to fix this is to make `mapState.iterator()`
return a `FlinkIterator` , aand `FlinkIterator` implement `AutoCloseable`, and
let `FlinkIterator` hold the `RocsdbIterator` until it closed. This way we only
need to seek one time when we iterate a map state. But this will broke the
interface flink has provided. @StefanRRichter What do you think?---
