History event

A history event is an immutable record appended to a workflow execution's history. The sequence of events is the canonical event-sourcing log; replaying it reconstructs the entire execution.

Aspect	Detail
Identity	(WorkflowExecution, EventID). EventID is a monotonically increasing per-execution counter.
Storage	history_node and history_tree tables (see schema/cassandra/temporal/schema.cql).
Branching	Reset and N-DC conflict resolution can branch the history tree.
Type catalog	temporal.api.enums.v1.EventType (proto in temporalio/api).

Code references

• History event read/write manager: common/persistence/history_manager.go.
• History event builder: service/history/historybuilder/.
• Public read API: WorkflowService.GetWorkflowExecutionHistory.

Notes

• "Event" in Temporal documentation always means history event, not the "event" of event-driven architectures.
• Events are versioned per cluster (see common/persistence/versionhistory/) so that conflict resolution between active/standby clusters can identify diverging branches.

Where to read more

• History service
• Replication
• Workflow execution