Cases2 cases

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1. IL-0553 CircleCI's orchestration database filled its transaction log volume, and no workflows or jobs started for 50 minutes

   CircleCI2026

   Symptoms

   On 6 October 2026 CircleCI pipelines were slow to be created and workflows and jobs were slow to start, in short bursts from 13:30 UTC and continuously from 15:30 UTC. From 15:48 to 16:38 UTC no workflows or jobs started at all, and pipelines triggered from 16:02 UTC failed.

   High latencyService outageThroughput degradationNode disk full

   Trigger

   Around 12:40 UTC, on top of the regular workload, anti-wraparound autovacuum runs on several of the largest tables of the orchestration service's database began writing transaction logs faster than the database could archive them.

   Root cause

   Capacity exhaustion

   Component

   DatabasePostgreSQL vacuumCI system

   Contributing factor

   Ignored early signalNo alert on limitSingle point of failure

   Detection

   Monitoring raised short alerts about errors in the orchestration service from 10:02 UTC, each clearing on its own. At 13:35 the alerts came back together with related alerts from several other services, and after they returned around 14:30 and engineers investigated further, an incident was declared at 14:54 UTC.

   Remediation

   • Changed the anti-wraparound autovacuum settings to help it finish faster
   • Moved the transaction logs onto the database's main storage volume, which took the database offline from 15:47 to 16:38 UTC
   • Changed database parameters to stop further maintenance runs from starting
   • Changed a database setting at 18:19 UTC to cut the time each write spent waiting on storage
   • Added database and server capacity to the systems that hand jobs to the execution fleet to clear the backlog faster

   Action items

   • Alert on how full the transaction log volume is and on how far archiving has fallen behind
   • Alert on the database maintenance that drives transaction log growth
   • Review all alerts so that noisy or sensitive alerts do not hide real issues
   • Tune how often and how aggressively autovacuum runs on the database
   • Track the size of the largest tables over time so they stay within safe limits
   • Remove the single transaction log bottleneck by splitting the service across several database instances or moving it to a distributed database
   • Make CircleCI's systems wait for the orchestration service to recover instead of failing jobs after retrying
   • Include specific impact and timing sooner in status page updates during long incidents

   Lessons

   CircleCI says the combination of alerts should have been recognised sooner: brief error alerts that cleared on their own were treated as routine, and nothing alerted on the transaction log volume or on archiving lag. Because every write of the orchestration service went through one database and one transaction log, a backlog in that log slowed every pipeline, workflow and job.

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2. IL-0328 A field type change in the database of CircleCI's job distribution service left all jobs stuck in "not running"

   CircleCI2021

   Symptoms

   From about 18:50 to 19:43 UTC on Monday, November 8, 2021, CircleCI customer jobs on all executors were blocked in a "not running" state. Errors and alerts appeared right after a deploy that changed a field type in the database of the job distribution service.

   Service outageHigh latencyScale-up failureCloud API rate limit exhausted

   Trigger

   At 18:50 UTC a deploy changed the type of a field in the PostgreSQL database of the job distribution service, in a way that was not backwards compatible.

   Root cause

   Faulty deployment

   Component

   DatabaseNode pool

   Contributing factor

   Ineffective rollbackExcessive blast radiusGap in automated tests

   Detection

   Errors and alerts related to the distribution failure appeared immediately after the 18:50 UTC deploy.

   Remediation

   • Rolled back the field type change, which did not clear the errors
   • Wrote, built and manually deployed a change that made the distribution system ignore the field
   • Manually scaled the primary compute cluster for the expected thundering herd of work
   • Monitored until processing was normal and resolved the incident

   Action items

   • Fix the gaps found in the testing strategy
   • Change how the distributor reacts to unexpected data so that this kind of deploy should not affect all jobs
   • Make recovery faster when unforeseen failures occur

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