TransactionConflictException
AWS TransactionConflictException means a DynamoDB transactional request conflicted with another concurrent item update (HTTP 400).
Last reviewed: February 16, 2026|Editorial standard: source-backed technical guidance
What Does Transaction Conflict Exception Mean?
DynamoDB rejected the transaction because another concurrent operation touched one or more of the same items, so writes must be retried with contention-aware backoff.
Common Causes
- -Concurrent transactions modify overlapping items and conflict at commit time.
- -High-contention partition keys cause frequent transactional write collisions.
- -Retry storms repeatedly target the same hot items without contention control.
- -Business workflow ordering allows multiple writers to race on the same entity state.
How to Fix Transaction Conflict Exception
- 1Retry conflicted transactions with exponential backoff and jitter.
- 2Reduce overlapping item sets per transaction where possible.
- 3Serialize high-contention workflows or introduce lock/lease coordination patterns.
- 4Use idempotent transaction design so safe retries do not duplicate side effects.
Step-by-Step Diagnosis for Transaction Conflict Exception
- 1Capture transaction request IDs and identify overlapping keys across competing writers.
- 2Analyze conflict frequency by partition key and transaction type.
- 3Correlate spikes with replay jobs, deploy events, or high-concurrency consumers.
- 4Inspect retry behavior to ensure retries are staggered and bounded.
Overlapping Item-Set Conflict Analysis
- -Identify exact item keys shared by conflicting transactions (example: two workers update same
order#123aggregate in parallel). - -Correlate conflict bursts with workflow fan-out patterns (example: replay job and real-time consumer overlap same key range).
Transaction Retry and Idempotency Controls
- -Validate exponential backoff with jitter and bounded retries (example: immediate synchronized retries keep colliding on same transaction set).
- -Enforce idempotent transaction tokens and deterministic write ordering (example: duplicate retry without idempotency causes extra contention and side effects).
How to Verify the Fix
- -Re-run transactional workload and confirm conflict rate drops to expected baseline.
- -Validate end-state correctness under concurrent test traffic.
- -Ensure retries no longer produce cascading write contention.
How to Prevent Recurrence
- -Design transactions to minimize overlapping key sets in hot paths.
- -Implement contention-aware scheduling for high-write workloads.
- -Continuously monitor conflict metrics and partition-key hotspots.
Pro Tip
- -route high-contention entities through per-key work queues so only one transactional writer executes at a time for each logical aggregate.
Decision Support
Compare Guide
HTTP 400 vs 422: Bad Request vs Unprocessable Content
Fix API payload issues faster by using 400 for malformed syntax and 422 for semantic validation failures, so clients correct format before business rules.
Playbook
Conflict and Concurrency Playbook (409 / 412 / OptimisticLock)
Use this playbook to separate true write conflicts from stale precondition failures, then apply safe re-fetch, optimistic-lock, and retry choices.
Playbook
CORS Error Fix Playbook (Preflight / Origin / Credentials)
Use this playbook to separate browser-enforced cross-origin policy failures from server-side CORS header and route defects and apply strict origin and credential controls safely.
Official References
Provider Context
This guidance is specific to AWS services. Always validate implementation details against official provider documentation before deploying to production.