**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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except OperationalError as e:
                timer.stop(send=False)
                raise e
            
            
            if len(task_instances_to_examine) == 0:
                self.log.debug("No tasks to consider for execution.")
                break
            
            task_instance_str = "\n\t".join(repr(x) for x in task_instances_to_examine)
            self.log.info(
                "%s tasks up for execution:\n\t%s", len(task_instances_to_examine), task_instance_str
            )
            for task_instance in task_instances_to_examine:
                pool_name = task_instance.pool
                pool_stats = pools.get(pool_name)
                if not pool_stats:
                    self.log.warning("Tasks using non-existent pool '%s' will not be scheduled", pool_name)
                    starved_pools.add(pool_name)
                    continue
                
                pool_num_starving_tasks.setdefault(pool_name, 0)
                pool_total = pool_stats["total"]
                open_slots = pool_stats["open"]
                if open_slots <= 0:
                    self.log.info(
                        "Not scheduling since there are %s open slots in pool %s", open_slots, pool_name
                    )
                    
                    pool_num_starving_tasks[pool_name] += 1