**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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ti.run()
    
    
    with mock.patch("airflow.models.dagrun.DagRun.verify_integrity") as mock_verify_integrity:
        dr.task_instance_scheduling_decisions()
        mock_verify_integrity.assert_not_called()
def test_calls_to_verify_integrity_with_mapped_task_increase_at_runtime(dag_maker, session):
    """
    Test increase in mapped task at runtime with calls to dagrun.verify_integrity
    """
    from airflow.models import Variable
    Variable.set(key="arg1", value=[1, 2, 3])
    @task
    def task_1():
        return Variable.get("arg1", deserialize_json=True)
    with dag_maker(session=session) as dag:
        @task
        def task_2(arg2):
            ...
        task_2.expand(arg2=task_1())
    dr = dag_maker.create_dagrun()
    ti = dr.get_task_instance(task_id="task_1")
    ti.run()
    dr.task_instance_scheduling_decisions()
    tis = dr.get_task_instances()
    indices = [(ti.map_index, ti.state) for ti in tis if ti.map_index >= 0]
    assert sorted(indices) == [
        (0, State.NONE),
        (1, State.NONE),
        (2, State.NONE),