Workflow eviction implemented with handle_eviction() callback, accompanied by a dedicated telemetry event handler to monitor eviction related events.

Workflow implementation in this sample performs the following steps:

1. Executes three activities sequentially.
2. Waits for a signal with a timeout. Since awaiting a signal may take a significant amount of time, the workflow is evicted to release resources.
3. After the signal wait concludes, the next three activities are executed sequentially. Workflow eviction is postponed until the activities are completed and signal is acknowledged.
4. Acknowledges the signal awaitable.
5. Executes the final set of three sequential activities; workflow eviction is allowed again.

All workflow activities take synthetic binary data as input, with the size specified by the first argument of the run() command.

Workflow eviction is managed by the temporal_sdk_workflow:handle_eviction/2 callback function implementation. Eviction behavior depends on the signal awaitable state, eviction strategy, and optionally history_size_bytes. Workflow is not evicted if the signal awaitable is in the requested state.

Available eviction strategies:

• always: Workflow is evicted regardless of the events history size.
• custom: If events history size exceeds 500,000 bytes, workflow is evicted on each workflow task completion request.
• never: Workflow is not evicted.

The handle_eviction/2 callback function is invoked after the gRPC RespondWorkflowTaskCompletedRequest call, which by default requests the Temporal server to dispatch new workflow task on the sticky queue. If the workflow execution is evicted after this call, it becomes impossible to notify the Temporal server that next workflow task should be dispatched on the regular task queue. As a result, the server dispatches a stale workflow task on the sticky queue. Such occurrences are reported via the task poller's sticky_miss event.

When the run() function executes, an event handler is attached to the [temporal_sdk, workflow, executor, stop] and [temporal_sdk,poller,execute,stop] telemetry events.

For [temporal_sdk, workflow, executor, stop] event workflow closing_state and event_id are logged. For [temporal_sdk, poller, execute, stop] event task_execute_status metadata is logged for the sticky_queue pollers.

Example run:

Elixir

iex(1)> WorkflowEviction.run(70_000, :custom)
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 21 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 57 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 63 -> completed
:ok
iex(2)> WorkflowEviction.run(100_000, :custom)
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 21 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 45 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 51 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 57 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 63 -> completed
:ok
iex(3)> WorkflowEviction.run(500_000, :custom)
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 9 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 15 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 21 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 45 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 51 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 57 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 63 -> completed
:ok
iex(4)> WorkflowEviction.run(1_000, :always)
[temporal_sdk,workflow,executor,stop]: 3 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 9 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 15 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 21 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 45 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 51 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 57 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 63 -> completed
:ok
iex(5)> WorkflowEviction.run(1_000, :never)
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 21 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 63 -> completed
:ok

Sample source: lib/workflow_eviction

Erlang

1> workflow_eviction:run(70_000, custom).
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 21 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 57 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 63 -> completed
ok
2> workflow_eviction:run(100_000, custom).
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 21 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 45 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 51 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 57 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 63 -> completed
ok
3> workflow_eviction:run(500_000, custom).
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 9 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 15 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 21 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 45 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 51 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 57 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 63 -> completed
ok
4> workflow_eviction:run(1_000, always).
[temporal_sdk,workflow,executor,stop]: 3 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 9 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 15 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 21 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 45 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 51 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 57 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_miss
[temporal_sdk,workflow,executor,stop]: 63 -> completed
ok
5> workflow_eviction:run(1_000, never).
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 21 -> evicted
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,poller,execute,stop]: sticky_hit
[temporal_sdk,workflow,executor,stop]: 63 -> completed
ok

Sample source: src/workflow_eviction

Note: This sample uses an aggressive workflow eviction strategy to illustrate the SDK's eviction approach. For a detailed discussion of practical eviction performance considerations, see the SDK Architecture - Workflow Eviction section.