Cases10 cases

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1. IL-0309 Preset's RDS PostgreSQL 14.7 to 17.9 upgrade in US East 1 ran out of storage and took Superset down for six hours

   Preset2026

   Symptoms

   A planned major version upgrade of Preset's production RDS PostgreSQL instances in US East 1, from 14.7 to 17.9, ran far past its maintenance window, and all customers on the us2a deployment could not reach Superset. After more than five hours the upgrade failed with "Postgres cluster is in a state where pg_upgrade cannot be completed successfully."

   Service outageUpgrade stall

   Trigger

   A planned major version upgrade of all RDS instances in production US East 1 from PostgreSQL 14.7 to 17.9, started with a ModifyDBInstance API call at 04:12 EDT.

   Root cause

   Capacity exhaustion

   Component

   DatabaseDatabase backups and snapshots

   Contributing factor

   Unrepresentative stagingUnverified assumptionUnknown limitLimited debug access

   Detection

   The planned upgrade was being watched as it ran: the snapshot's I/O was observed at 05:28 EDT, the incident was posted on the status page at 06:00 EDT and an AWS support ticket was opened at 07:26 EDT.

   Remediation

   • AWS rolled the failed upgrade back automatically, and the instance restarted on PostgreSQL 14.15 at 10:13 EDT

   Action items

   • Rehearse the upgrade against a full production-scale dataset to check storage and timing estimates before any future major version upgrade

   Lessons

   Preset learned that RDS takes a full, non-incremental snapshot before a major version upgrade, so the duration of the daily incremental snapshots and of the upgrades in other regions said nothing about how long the pre-upgrade snapshot would take on this instance. The S3 snapshot throughput limit of about 30–45MB/s only becomes visible during such full snapshots, which are rare in normal operation.

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2. IL-0484 Slurm 24.05 to 25.05 upgrade broke GPU configuration on MIT CSAIL's cluster, and a failed downgrade kept it down

   MIT CSAIL2025

   Symptoms

   After a planned full day of downtime on Monday, September 8, 2025, to upgrade the MIT CSAIL Slurm compute cluster from Slurm 24.05 to Slurm 25.05, the Infrastructure Group found on Tuesday morning that the upgraded Slurm packages had been built without a feature the cluster needs for correct GPU configuration. The cluster did not return to normal operation until Wednesday morning, after a downgrade failed and the cluster was rebuilt.

   Upgrade stallService outage

   Trigger

   The upgrade from Slurm 24.05 to Slurm 25.05 on September 8 installed packages that were not compiled with a feature required for correct GPU configuration.

   Root cause

   Breaking change in an upgrade

   Component

   Slurm job schedulerDatabase backups and snapshots

   Contributing factor

   Ineffective rollbackUntested backup

   Detection

   On the Tuesday morning after the maintenance day, the team discovered that the upgraded Slurm packages were not compiled with the feature needed for GPU configuration.

   Remediation

   • Downgraded Slurm to the previous known-working version
   • Reinstalled the OS on all compute nodes and handled the nodes left in an intermediate state one by one
   • Re-deployed the cluster from scratch on a clean database

   Action items

   • Improve the testing and deployment processes based on the lessons of the outage

   Lessons

   The downgrade exposed flaws in the deployment and testing process: the deployment service could not reinstall every compute node at once, and the upgrade plan did not allow a simple downgrade or a working restore of the controller and database from backup.

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3. IL-0242 Both PostgreSQL servers behind matrix.org were lost during a disk expansion, and the homeserver was down for 24 hours

   Matrix.org Foundation2025

   Symptoms

   On 2 September 2025 the matrix.org homeserver went down at 17:45 UTC and stayed down until 18:00 UTC the next day. Both machines of its PostgreSQL cluster were out of action: the original primary had lost its RAID array during a disk expansion, and the data directory of the new primary had been deleted by mistake.

   Service outageData loss

   Trigger

   During maintenance to add drives, an existing drive disappeared from the primary database server's RAID 10 array at 11:17 UTC, which led to a failover and a rebuild of that server. The outage itself began when the data directory of the new primary on db-01 was deleted while clearing a failed restore on db-02.

   Root cause

   Operator error

   Component

   DatabaseDatabase backups and snapshotsDatabase replication

   Contributing factor

   Overlapping failuresHarmful manual actionUnpatched known bugNo safeguard on destructive change

   Detection

   Monitoring fired when the drive disappeared from db-02's RAID array at 11:17 UTC, and Mythic Beasts confirmed the issue. The team realised it had deleted db-01's data directory, and the backend team was then paged, an incident was opened and an emergency was declared.

   Remediation

   • Created a fresh RAID 10 array on db-02
   • Unblocked WAL archiving from the new primary on db-01 to S3
   • Started restoring db-02 from the S3 backups with wal-g
   • Shut down Synapse and the damaged primary database
   • Remounted the data partition of db-01 read-only
   • Copied the WALs missing from S3 from db-01 to db-02
   • Updated wal-g and patched it to continue from the partial restore
   • Configured a restore_command wrapper that fetched WALs from S3 and the local files, and replayed them in standby mode
   • Promoted db-02 to primary and restarted Synapse
   • Ran backups against the primary while no replica existed
   • Rebuilt db-01 as a replica from a base backup of db-02

   Action items

   • Run pg_repack to reclaim free space
   • Take incremental backups more often, since they restore faster than WAL replay
   • Reduce Synapse's storage requirements
   • Consider changing the terminal background colour by the database's role, for example by watching for the standby.signal file
   • Consider wrapper scripts around sensitive commands, such as an alias for rm, and automating operations such as starting a base backup from primary to secondary
   • Shorten the recovery time, with infrastructure from service providers
   • Upgrade wal-g on all servers and repeat disaster recovery testing with it
   • Explore ZFS local snapshots at the next hardware refresh
   • Make status.matrix.org the source of truth during incidents and keep social media updated

   Lessons

   Most of the difficulty came from the size of the database: restoring 51TB and replaying WALs took far longer than hoped, and incremental backups restore much faster than WAL replay. Running a destructive command on the wrong server was the turning point, and Matrix.org looks for better tooling and processes rather than blaming the individual; working as a trio did not catch the mistake, and server names that suggest a role caused confusion because a primary and a secondary swap roles. The recovery lost no data, but the recovery time needs to be shorter, and the wal-g versions on the disaster recovery server and the production servers had drifted apart.

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4. IL-0311 BattleMetrics' primary PostgreSQL went read-only at transaction ID wraparound, breaking the website and RCON updates

   BattleMetrics2022

   Symptoms

   At 03:23 UTC on 27 March 2022, BattleMetrics' primary PostgreSQL database, which holds all account, server and player information, went into read-only mode. Users first saw the website fail to load, and soon RCON updates and queries began to fail as well.

   Writes rejectedService outage

   Trigger

   A corruption of the index on the player identifiers table, which BattleMetrics' logs place at about 26 February 2022, made every vacuum job fail, so transaction IDs kept climbing until Postgres stopped accepting writes on 27 March.

   Root cause

   Data loss or corruption

   Component

   DatabasePostgreSQL vacuumDatabase replicationDatabase backups and snapshots

   Contributing factor

   Monitoring blind spotOverlapping failuresNo headroom

   Detection

   Users failed to load the website and reported it as their API keys expired, then RCON updates and queries began to fail, and the team found that the main database no longer accepted writes.

   Remediation

   • Shut the database down and dropped the corrupted player identifiers index in single-user mode
   • Ran the vacuum again, which succeeded and let the database accept writes
   • Rebuilt the player identifier index, which took about two hours
   • Shut down the query workers and gave RCON updates priority
   • Pointed services at the new Postgres primary
   • Bootstrapped new replicas one after another to take load off the primary
   • Restarted queries with throttling, prioritised by server population and rank, after RCON updates had caught up

   Action items

   • Monitor errors in the Postgres logs
   • Monitor and alert on transaction IDs
   • Set up a logical replica in addition to physical replication
   • Build a faster network to speed up recovery from failure

   Lessons

   BattleMetrics names skipping health checks on transaction ID size as its critical mistake: the index corruption silently broke vacuum for a month, and without monitoring of transaction IDs nobody saw the database approach wraparound. Because the corruption had been replicated to the replicas, failing over did not help, and the backup servers and downloadable backups carried the same corruption. The team also found that, contrary to the error message, a full vacuum on a server in wraparound protection does not need single-user mode, and chose to run a slow, delayed service over no service while replicas were rebuilt.

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5. IL-0325 DigitalOcean's control panel and API were down for 4 hours 56 minutes after the production primary database was deleted

   DigitalOcean2017

   Symptoms

   At 10:24 AM EDT on April 5th, 2017, DigitalOcean began to receive alerts that its public services were not working, and by 10:27 the team had verified that the production database on the primary had been deleted. The control panel and the API were unavailable for four hours and fifty-six minutes: running Droplets kept working, but no new Droplets or other resources could be created or managed.

   Service outage

   Trigger

   A process performing automated testing had been misconfigured with production credentials, and the production primary database was deleted.

   Root cause

   Configuration change

   Component

   DatabaseDatabase replicationDatabase backups and snapshots

   Contributing factor

   No safeguard on destructive change

   Detection

   Alerts at 10:24 AM EDT that public services were not functioning; within three minutes the team found that the primary database had been deleted.

   Remediation

   • Began recovery from a time-delayed database replica
   • Took a backup of the time-delayed replica
   • Copied the backup to the primary and recovered it
   • Copied the backups to the replicas until all systems were restored

   Action items

   • Drastically reduce access to the primary system for certain actions
   • Upgrade network connectivity between database servers
   • Update hardware to speed up recovery
   • Assess further safeguards against developer error
   • Improve the processes around data recovery
   • Explore ways to provide better real-time information to customers during future customer-impacting events

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