# Prometheus monitoring

Prometheus is a widely popular tool for monitoring and alerting a wide variety of systems. A distributed cluster offers a number of Prometheus metrics if the prometheus_client package is installed. The metrics are exposed in Prometheus’ text-based format at the `/metrics` endpoint on both schedulers and workers.

## Available metrics

Apart from the metrics exposed per default by the prometheus_client, schedulers and workers expose a number of Dask-specific metrics.

### Scheduler metrics

The scheduler exposes the following metrics about itself:

dask_scheduler_clients

  Number of clients connected

dask_scheduler_client_connections_added_total

  Total number of client connections added to the scheduler

  Note

  This metric does not count distinct clients. If a client disconnects and reconnects later on, it will be counted twice.

dask_scheduler_client_connections_removed_total

  Total number of client connections removed from the scheduler

  Note

  This metric does not count distinct clients. If a client disconnects, then reconnects and disconnects again, it will be counted twice.

dask_scheduler_desired_workers

  Number of workers scheduler needs for task graph

dask_scheduler_gil_contention_seconds_total

  Value representing cumulative total of potential GIL contention, in the form of cumulative seconds during which any thread held the GIL locked. Other threads may or may not have been actually trying to acquire the GIL in the meantime.

  Note

  Requires `gilknocker` to be installed, and `distributed.admin.system-monitor.gil.enabled` configuration to be set.

dask_scheduler_gc_collection_seconds_total

  Total time spent on garbage dask_scheduler_gc_collection_seconds_total

  Note

  Due to measurement overhead, this metric only measures time spent on garbage collection for generation=2

dask_scheduler_workers

  Number of workers known by scheduler

dask_scheduler_workers_added_total

  Total numbers of workers added to the scheduler

dask_scheduler_workers_removed_total

  Total number of workers removed from the scheduler

dask_scheduler_last_time_total

  Cumulative SystemMonitor time

dask_scheduler_tasks

  Number of tasks known by scheduler

dask_scheduler_tasks_suspicious_total

  Total number of times a task has been marked suspicious

dask_scheduler_tasks_forgotten_total

  Total number of processed tasks no longer in memory and already removed from the scheduler job queue.

  Note

  Task groups on the scheduler which have all tasks in the forgotten state are not included.

dask_scheduler_tasks_compute_seconds_total

  Total time (per prefix) spent computing tasks

dask_scheduler_tasks_transfer_seconds_total

  Total time (per prefix) spent transferring

dask_scheduler_tasks_output_bytes

  Current size of in memory tasks, broken down by task prefix, without duplicates. Note that when a task output is transferred between worker, you’ll typically end up with a duplicate, so this measure is going to be lower than the actual cluster-wide managed memory. See also `dask_worker_memory_bytes`, which does count duplicates.

dask_scheduler_task_groups

  Number of task groups known by scheduler

dask_scheduler_prefix_state_totals_total

  Accumulated count of task prefix in each state

dask_scheduler_tick_count_total

  Total number of ticks observed since the server started

dask_scheduler_tick_duration_maximum_seconds

  Maximum tick duration observed since Prometheus last scraped metrics. If this is significantly higher than what’s configured in `distributed.admin.tick.interval` (default: 20ms), it highlights a blocked event loop, which in turn hampers timely task execution and network comms.

### Semaphore metrics

The following metrics about `Semaphore` objects are available on the scheduler:

dask_semaphore_max_leases

  Maximum leases allowed per semaphore.

  Note

  This will be constant for each semaphore during its lifetime.

dask_semaphore_active_leases

  Amount of currently active leases per semaphore

dask_semaphore_pending_leases

  Amount of currently pending leases per semaphore

dask_semaphore_acquire_total

  Total number of leases acquired per semaphore

dask_semaphore_release_total

  Total number of leases released per semaphore

  Note

  If a semaphore is closed while there are still leases active, this count will not equal `dask_semaphore_acquire_total` after execution.

dask_semaphore_average_pending_lease_time_s

  Exponential moving average of the time it took to acquire a lease per semaphore

  Note

  This only includes time spent on scheduler side, it does not include time spent on communication.

  Note

  This average is calculated based on order of leases instead of time of lease acquisition.

### Work-stealing metrics

If Work Stealing is enabled, the scheduler exposes these metrics:

dask_stealing_request_count_total

  Total number of stealing requests

dask_stealing_request_cost_total

  Total cost of stealing requests

### Worker metrics

The worker exposes these metrics about itself:

dask_worker_tasks

  Number of tasks at worker

dask_worker_threads

  Number of worker threads

dask_worker_gil_contention_seconds_total

  Value representing cumulative total of potential GIL contention, in the form of cumulative seconds during which any thread held the GIL locked. Other threads may or may not have been actually trying to acquire the GIL in the meantime.

  Note

  Requires `gilknocker` to be installed, and `distributed.admin.system-monitor.gil.enabled` configuration to be set.

dask_worker_gc_collection_seconds_total

  Total time spent on garbage dask_scheduler_gc_collection_seconds_total

  Note

  Due to measurement overhead, this metric only measures time spent on garbage collection for generation=2

dask_worker_latency_seconds

  Latency of worker connection

dask_worker_memory_bytes

  Memory breakdown

dask_worker_transfer_incoming_bytes

  Total size of open data transfers from other workers

dask_worker_transfer_incoming_count

  Number of open data transfers from other workers

dask_worker_transfer_incoming_count_total

  Total number of data transfers from other workers since the worker was started

dask_worker_transfer_outgoing_bytes

  Size of open data transfers to other workers

dask_worker_transfer_outgoing_bytes_total

  Total size of open data transfers to other workers since the worker was started

dask_worker_transfer_outgoing_count

  Number of open data transfers to other workers

dask_worker_transfer_outgoing_count_total

  Total number of data transfers to other workers since the worker was started

dask_worker_concurrent_fetch_requests

  Deprecated: This metric has been renamed to `dask_worker_transfer_incoming_count`.

dask_worker_tick_count_total

  Total number of ticks observed since the server started

dask_worker_tick_duration_maximum_seconds

  Maximum tick duration observed since Prometheus last scraped metrics. If this is significantly higher than what’s configured in `distributed.admin.tick.interval` (default: 20ms), it highlights a blocked event loop, which in turn hampers timely task execution and network comms.

dask_worker_spill_bytes_total

  Total size of spilled/unspilled data since the worker was started; in other words, cumulative disk I/O that is attributable to spill activity. This includes a `memory_read` measure, which allows to derive cache hit ratio:

      cache hit ratio = memory_read / (memory_read + disk_read)

dask_worker_spill_count_total

  Total number of spilled/unspilled keys since the worker was started; in other words, cumulative disk accesses that are attributable to spill activity. This includes a `memory_read` measure, which allows to derive cache hit ratio:

      cache hit ratio = memory_read / (memory_read + disk_read)

dask_worker_spill_time_seconds_total

  Total amount of time that was spent spilling/unspilling since the worker was started, broken down by activity: (de)serialize, (de)compress, (un)spill.

If the crick package is installed, the worker additionally exposes:

dask_worker_tick_duration_median_seconds

  Median tick duration at worker

dask_worker_task_duration_median_seconds

  Median task runtime at worker

dask_worker_transfer_bandwidth_median_bytes

  Bandwidth for transfer at worker