ActiveRecord::Deadlocked: PG::TRDeadlockDetected Ruby / Rails Origin: Application & API Last updated 5 Nov 2026

Rails: ActiveRecord::Deadlocked: PG::TRDeadlockDetected: ERROR: deadlock detected

Two transactions locked rows in opposite orders, so PostgreSQL aborted one.

Exact message you may see ActiveRecord::Deadlocked: PG::TRDeadlockDetected: ERROR: deadlock detectedMysql2::Error: Deadlock found when trying to get lock; try restarting transactionActiveRecord::Deadlocked: Mysql2::Errordeadlock detected DETAIL: Process 123 waits for ShareLock on transaction
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Seen on: Ruby PostgreSQL

Meaning

Keep transactions short, update rows in a consistent order (sort ids before update), use lock! consistently, avoid mixing row locks and table scans, and retry on ActiveRecord::Deadlocked (Rails 5.2+ raises it for MySQL/PostgreSQL). Background jobs that update the same rows concurrently are typical.

Common causes

  • Concurrent jobs updating rows in different orders
  • Long transactions
  • update_all/bulk updates overlapping
  • Foreign key locks (parent/child updates)
  • Unordered IN (...) updates

⚡ Quick fix

  1. Sort ids and lock in a consistent order
  2. Shorten transactions
  3. Rescue ActiveRecord::Deadlocked and retry

Detailed fix by platform

Rails

  1. Order.where(id: ids.sort).order(:id).lock.each { |o| o.update!(...) }

How to diagnose

  1. Order — Consistent?
  2. Duration — Short?
  3. Retry — Handled?

🔧 Still not fixed?

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Where this error sits

Origin: Application & API. Errors that are often confused with or caused by this one (click to open):

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