PyFlink local mode doesn't give a consistent output on top-k, while standalone mode does

[Yik San Chan]

Hi community,

I have a job that exercises top-n query as described in https://ci.apache.org/projects/flink/flink-docs-release-1.13/zh/docs/dev/table/sql/queries/topn/. You can find the job in https://github.com/YikSanChan/pyflink-quickstart/blob/26e7c09aaa1167b13b981586ffb0e7d6bb6cf053/topk.py

What I find interesting:

- In local mode, i.e. `python topk.py`, I am not able to get consistent output.

- In standalone mode, i.e., `~/softwares/flink-1.12.0/bin/flink run -d -pyexec /usr/local/anaconda3/envs/pyflink-quickstart/bin/python -py topk.py`, I always get consistent output.

By consistent output, I mean the output order is strictly respected:

```

+I(1,100)

-U(1,100)

+U(1,100,101)

+I(2,201)

-U(2,201)

+U(2,201,200)

-U(2,201,200)

+U(2,201,200,202)

-U(2,201,200,202)

+U(2,201,202)

-U(2,201,202)

+U(2,201,202,203)

-U(1,100,101)

+U(1,100,101,102)

-U(1,100,101,102)

+U(1,101,102)

-U(1,101,102)

+U(1,101,102,103)

-U(1,101,102,103)

+U(1,102,103)

-U(1,102,103)

+U(1,102,103,104)

-U(2,201,202,203)

+U(2,202,203)

-U(2,202,203)

+U(2,202,203,204)

```

While `python topk.py` gives a somewhat random (and not reasonable) output everytime I run it, for example,

```

6> +I(1,102)
6> +I(2,202)
6> -U(2,202)
6> +U(2,202,203)
6> -U(1,102)
6> +U(1,102,104)
6> -U(1,102,104)
6> +U(1,102,104,103)
6> -U(2,202,203)
6> +U(2,202,203,201)
6> -U(2,202,203,201)
6> +U(2,202,203)
6> -U(2,202,203)
6> +U(2,202,203,204)

```

Note that I use the default flink-conf.yaml, which means the slot number is always 1. Any idea why?

Best,

Yik San