Race Conditions in n8n AI Agent Workflows (and the Fix)

Description and use

In n8n, concurrent executions can double‑book a resource when an AI Agent extends the check‑then‑act window. The fix is to atomically claim the resource, use idempotency keys, and re‑check the real system before writing.

Problem

Concurrent executions in n8n can double‑book a resource when an AI Agent node extends the check‑then‑act window, leading to race conditions that are not caught by single‑request testing.

Outcome

Implementing an atomic claim, idempotency keys, and a final re‑check eliminates double‑booking in n8n AI Agent workflows, even under high concurrency.

Workflow

• 1. Claim the slot in a store with a unique constraint (e.g., Postgres INSERT ON CONFLICT DO NOTHING).
• 2. If claim succeeds, generate an idempotency key for the booking action.
• 3. Perform the booking via the tool or API, passing the idempotency key.
• 4. Re‑check the real system (calendar) immediately before the final write; if the slot is no longer free, abort and return a “taken” response.
• 5. If any step fails, route to an error handling path or retry logic.

Evidence

check shared state (a calendar, a stock count, a CRM record), then act on it, with nothing stopping a second execution from checking in between.

Source

The fix is to claim before you act, give every business action an idempotency key, and re-check the real system right before the final write.

Source

INSERT INTO slot_claims (slot_id, execution_id) VALUES ('2026-10-08T15:00', 'EXECUTION_ID') ON CONFLICT (slot_id) DO NOTHING RETURNING slot_id;

Source