Concurrency events

Concurrency events cover two categories: CRUD lifecycle events emitted when concurrency limits are created, updated, or deleted, and slot events emitted when concurrency slots are acquired and released. For more on concurrency limits, see Global concurrency limits.

Concurrency limit lifecycle events

prefect.concurrency-limit.created

Emitted when a new concurrency limit is created.

Resource

Label	Description
prefect.resource.id	prefect.concurrency-limit.{uuid}
prefect.resource.name	Concurrency limit name

Related resources

This event has no related resources.

Payload

For global (v2) concurrency limits:

Field	Type	Description
name	string	Concurrency limit name
limit	integer	Maximum number of concurrent slots
active	boolean	Whether the limit is currently active
slot_decay_per_second	float	Rate at which slots are released over time

For tag-based (v1) concurrency limits:

Field	Type	Description
tag	string	Tag this limit applies to
concurrency_limit	integer	Maximum number of concurrent runs

prefect.concurrency-limit.updated

Emitted when a concurrency limit's configuration is changed.

Resource

Same as prefect.concurrency-limit.created.

Related resources

This event has no related resources.

Payload

Same as prefect.concurrency-limit.created.

prefect.concurrency-limit.deleted

Emitted when a concurrency limit is deleted.

Resource

Same as prefect.concurrency-limit.created.

Related resources

This event has no related resources.

Payload

Same as prefect.concurrency-limit.created.

Slot events

prefect.concurrency-limit.acquired

Emitted when concurrency slots are acquired for a named limit.

Resource

Label	Description
prefect.resource.id	prefect.concurrency-limit.{uuid}
prefect.resource.name	Concurrency limit name
slots-acquired	Number of slots acquired in this request
limit	Maximum number of slots for this limit

Related resources

Resource ID pattern	Role	When present
prefect.concurrency-limit.{uuid}	concurrency-limit	One entry per other limit in the same acquisition batch (when acquiring multiple limits at once)

Payload

This event has no payload.

prefect.concurrency-limit.released

Emitted when concurrency slots are released for a named limit. Uses the follows field to link back to the corresponding acquired event.

Resource

Same as prefect.concurrency-limit.acquired.

Related resources

Same as prefect.concurrency-limit.acquired.

Payload

This event has no payload.

Legacy v1 concurrency events

<Note> These events are emitted by the legacy tag-based concurrency limit system. For new concurrency limits, use global concurrency limits which emit the events documented above. </Note>

prefect.concurrency-limit.v1.acquired

Emitted when a legacy tag-based concurrency slot is acquired.

Resource

Label	Description
prefect.resource.id	prefect.concurrency-limit.v1.{uuid}
prefect.resource.name	Tag name
limit	Maximum number of slots
task_run_id	ID of the task run acquiring the slot

Related resources

Resource ID pattern	Role	When present
prefect.concurrency-limit.v1.{uuid}	concurrency-limit	One entry per other limit in the same acquisition batch

Payload

This event has no payload.

prefect.concurrency-limit.v1.released

Emitted when a legacy tag-based concurrency slot is released.

Resource

Same as prefect.concurrency-limit.v1.acquired.

Related resources

Same as prefect.concurrency-limit.v1.acquired.

Payload

This event has no payload.