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 |
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 |
| 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.
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.
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 |
| 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.
Same as prefect.concurrency-limit.acquired.
Payload
This event has no payload.
Legacy v1 concurrency events
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.
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 |
| 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.
Same as prefect.concurrency-limit.v1.acquired.
Payload
This event has no payload. 
