Database Deadlock proxy versus origin split response

When this happens

Use this when a cdn, load balancer, reverse proxy, or waf sits in front of the service. Do not stop at the screen message; validate whether the edge/proxy or the origin server creates the failure first.

Symptom checklist

• Deadlock appears repeatedly in the Database UI or logs.
• slow query, locks, pool, index, charset differs between successful and failed requests.
• The issue appears only after separating SQL error from application transaction behavior.
• It often follows deploys, permission changes, configuration edits, or data refreshes.

Likely causes

• Deadlock specifically changes the investigation surface for Database: verify the exact failing object, route, user, and timestamp before applying the broader pattern.
• Two requests write the same logical record at the same time.
• A retry repeats an insert without an idempotency key.
• The unique index or remote branch is correct but the application does not handle conflict paths.
• Transaction lock order differs between workers.
• A batch job reprocesses already imported rows.
• For the proxy versus origin split case, the first useful clue is whether the edge/proxy or the origin server creates the failure.

First 1-minute checks

1. Write down the first failure time, latest change, affected user, path, and object ID.
2. Compare slow query, locks, pool, index, charset for success and failure in the same window.
3. Test the hypothesis: duplicate or lock conflict caused by concurrent writes, missing idempotency, unique keys, transaction order, or remote state drift.
4. Classify this as proxy versus origin split: whether the edge/proxy or the origin server creates the failure.
5. Capture current values before changing configuration.

First evidence

Treat Deadlock as a proxy versus origin split case. First collect evidence for whether the edge/proxy or the origin server creates the failure.

Output examples

Normal output

Direct origin and routed proxy return equivalent status and headers.

Failing output

Origin succeeds but proxy fails, or proxy succeeds while direct origin exposes the real backend error.

Output-to-action branches

• A CDN, load balancer, reverse proxy, or WAF sits in front of the service.
  Test direct origin and routed traffic separately, then change only the layer that differs.
• The working and failing outputs differ.
  Act on the differing layer first: For Deadlock, apply the fix only after reproducing the same condition and saving the before/after evidence for this exact code.
• Command output is normal but users still fail.
  Separate browser cache, cookies, permissions, and network location before declaring it fixed.

Do not do this

• Do not assume the CDN error code is the application root cause.
• Do not change multiple layers before identifying the failing layer.
• Do not delete production data, grant broad permissions, or disable security controls as a first response.

Evidence quality

Auto-generated operator draft: includes issue-specific causes, commands, output branches, and unsafe-action warnings. Official-source links and real incident validation are queued for enrichment.

Commands to run first

grep -R "Deadlock" ./logs

SHOW PROCESSLIST;

SHOW ENGINE INNODB STATUS\G

EXPLAIN SELECT ...

grep -R "Deadlock" ./logs

grep -R "duplicate\|deadlock\|conflict\|lock\|rejected" ./logs

git fetch --all --prune

git status --short --branch

curl -Iv https://example.com --resolve example.com:443:ORIGIN_IP

Fix order

1. Record the full Deadlock message, failing URL, user, object ID, and latest change.
2. Collect issue-specific evidence for duplicate or lock conflict caused by concurrent writes, missing idempotency, unique keys, transaction order, or remote state drift.
3. Compare the failing case with a successful case before editing settings.
4. If this is the proxy versus origin split branch, Test direct origin and routed traffic separately, then change only the layer that differs.
5. Re-check with the same command and URL, then record the normal output.

Actions by cause

• For Deadlock, apply the fix only after reproducing the same condition and saving the before/after evidence for this exact code.
• Add an idempotency key or upsert path for repeated writes.
• Use unique constraints intentionally and handle duplicate exceptions.
• Sort lock acquisition order consistently.
• Split batch reprocessing from live writes.
• Fetch remote state before retrying rejected pushes or tags.
• For the proxy versus origin split branch, Test direct origin and routed traffic separately, then change only the layer that differs.

Evidence links

• MySQL error reference official
• PostgreSQL documentation official

Verification metadata

• operator-draft
• official-reference-linked
• 2026-07-23

Update queue

• Review cadence
  weekly-source-review
• Next enrichment
  Add one official-source check and one real output example for Database Deadlock.

Environment-specific checks

• Shared hosting, proxies, VPNs, or CDN layers can change SQL error from application transaction behavior results.
• Do not trust only the Database UI; compare command output.
• Japanese hosting panels may show completion before DNS or SSL fully propagates.
• Test from both office and external networks.

Prevent it next time

• Store normal examples for slow query, locks, pool, index, charset.
• Add indexing, pool tuning, transaction scope, charset alignment to the release checklist.
• Keep recurring errors in the same note format.
• Split alerts by error rate, latency, certificates, disk, and permission changes.

Related notes

• MySQL Too many connections
• MySQL Duplicate entry fix note
• MySQL Deadlock fix note
• PostgreSQL relation does not exist fix note
• MySQL Duplicate entry fix note 2
• MySQL Deadlock fix note 2
• PostgreSQL relation does not exist fix note 2
• MySQL Duplicate entry fix note 3