Top active series per tenant on a concrete ingester

topk by (pod) (10,
    sum by (user, pod) ( # get in-memory series for each tenant on each pod
        cortex_ingester_memory_series_created_total{namespace="cortex-prod-10", pod="ingester-zone-c-70"} - cortex_ingester_memory_series_removed_total{namespace="cortex-prod-10", pod="ingester-zone-c-70"}
    ))