**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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"""
        Clears import errors for files that no longer exist.
        :param file_paths: list of paths to DAG definition files
        :param session: session for ORM operations
        """
        query = session.query(errors.ImportError)
        if file_paths:
            query = query.filter(~errors.ImportError.filename.in_(file_paths))
        query.delete(synchronize_session="fetch")
        session.commit()
    def _log_file_processing_stats(self, known_file_paths):
        """
        Print out stats about how files are getting processed.
        :param known_file_paths: a list of file paths that may contain Airflow
            DAG definitions
        :return: None
        """