**Description**


It would be great if the metrics we publish in Airflow change to include TAGs for "variable" parts of those (such as dag_id, task_id, pool name) rather than being part of the metrics.

See here: https://airflow.apache.org/docs/1.10.12/metrics.html, https://airflow.readthedocs.io/en/latest/logging-monitoring/metrics.html  - those variable parts should be tags.

We might consider to change those metrics by default in 2.0 and possibly introduce a backport in 1.10.13 to allow people to migrate.


**Use case / motivation**

Having the variable parts of the metrics makes it really difficult to aggregate the metrics. Seems that statsd python library does not support tags, but there are possible solutions by installing extensions:

https://stackoverflow.com/questions/49852654/sending-statsd-metrics-with-tags-from-python-client

**Related Issues**

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"""
        Test that when a processor already exist with a filepath, a new processor won't be created
        with that filepath. The filepath will just be removed from the list.
        """
        manager = DagFileProcessorManager(
            dag_directory="directory",
            max_runs=1,
            processor_timeout=timedelta(days=365),
            signal_conn=MagicMock(),
            dag_ids=[],
            pickle_dags=False,
            async_mode=True,
        )
        file_1 = "file_1.py"
        file_2 = "file_2.py"
        file_3 = "file_3.py"
        manager._file_path_queue = collections.deque([file_1, file_2, file_3])
        
        manager._processors[file_1] = MagicMock()
        
        manager.start_new_processes()
        
        
        
        
        
        assert file_1 in manager._processors.keys()
        assert file_2 in manager._processors.keys()
        assert collections.deque([file_3]) == manager._file_path_queue
    def test_set_file_paths_when_processor_file_path_not_in_new_file_paths(self):