caigy

This design requires updating rocketmq-client, which might bring cost for users to update rocketmq-client. I've some suggestions: 1. `accessKey` should be defined as a globally unique string, so that complexity...

@Oliverwqcwrw Please fix test errors: ``` Tests run: 25, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 27.275 sec

@Oliverwqcwrw Please refer to the result of Travis Ci: https://github.com/apache/rocketmq/pull/4637/checks?check_run_id=7819279185

@Oliverwqcwrw Actually your branch is checked out. 

I found `System.nanoTime()` was used instead of `System.currentTimeMillis()`, will it bring benefits to performance improvement? It also brings some conversion between nanosecond variables and config values defined in millisecond.

> > Is it possible to add the logic of regular flushing of `IndexFile`, just like refreshing `ConsumeQueue`, `StoreCheckpoint`, and `CommitLog` regularly. > > i find the wrong test in...

@seedscoder You may use `docker inspect` command to find more information.

@Euthpic `resources/application.properties` is in source code of [rocketmq-dashboard](https://github.com/apache/rocketmq-dashboard), please check if it can be injected by environment variables. For `users.properties`, you should create one and put it the folder `${rocketmq.config.dataPath}`...

@shendongsd Is there an issue related to this PR? Would you also support `preferredDuringSchedulingIgnoredDuringExecution`, or why not?

@linjiemiao Good idea! Would you like to submit a PR?