- Software and systems
- Database
40P01
PostgreSQL 40P01: deadlock_detected
Evidence linked to this decision
View source: PostgreSQL 18 Appendix A: Error CodesRisk level
High
Professional inspection is recommended.
Urgency
Medium
Quick answer
SQLSTATE 40P01 (deadlock_detected) means PostgreSQL detected a lock cycle and aborted one transaction to break it. Diagnose the named condition before retrying.
Safety first
Safe checks you can perform
- Reconstruct the lock order from the server log
What a technician must be able to justify
A technician is coming
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Reconstruct the lock order from the server log
Use PostgreSQL's deadlock log to identify both transactions, relations and statements. Roll back and retry the complete victim transaction only when idempotent, with a cap. Fix recurrence by acquiring shared resources in one consistent order and keeping transactions short.
Evidence: PostgreSQL 18 Appendix A: Error Codes · PostgreSQL transaction isolation · PostgreSQL ROLLBACK
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Virtual technician
Does 40P01 still appear after these checks?
This guided flow uses the exact code and your answers to choose a test, an expected result and the next branch.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Software and systems
- Brand
- PostgreSQL
- Product type
- Database
Known code variants
- deadlock_detected
- PostgreSQL 40P01
- SQLSTATE 40P01
What it means
PostgreSQL assigns 40P01 to deadlock_detected in Class 40 — Transaction Rollback. Applications should branch on the stable SQLSTATE and structured error fields, not localized message text.
Symptoms and causes
Probable causes · in order
- Likely trigger in this requestCommon
Concurrent transactions acquired overlapping locks in inconsistent order and each waited for the other.
Evidence: PostgreSQL 18 Appendix A: Error Codes · PostgreSQL transaction isolation · PostgreSQL ROLLBACK
Sources and technical references
- 1
PostgreSQL 18 Appendix A: Error Codes
PostgreSQL Global Development Group · 2026 · official_doc
- 2
PostgreSQL transaction isolation
PostgreSQL Global Development Group · 2026 · official_doc
- 3
PostgreSQL Global Development Group · 2026 · official_doc
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