IL-0287 MongoDB · 2025-10-07databaseobservability
One overloaded shard of MongoDB's internal monitoring database delayed Atlas metrics, alerts and cluster operations
MongoDB Atlas and Cloud Manager monitoring systems rely on an internal, sharded database cluster. High-traffic collections in it had not been sharded, so their load was concentrated on one shard and created a hotspot when load rose, and inefficient query patterns such as full collection scans added strain on that shard during normal operation. The postmortem dates the incident to October 6 and 7, when a rollout of an updated internal software version produced a temporary spike in resource demand, and together these overwhelmed the shard and delayed metrics ingestion and Atlas cluster operations. MongoDB applied mitigations to stabilise the system and then fixed the long-term causes; the status page marked the incident resolved at 20:03 UTC on 7 October 2025. There was no loss of data and no effect on the availability or performance of customer applications.
- Severity
- –
- Scope
- Delayed or missing metrics in Atlas and Cloud Manager dashboards, Host Down alerts not firing, and delayed Atlas cluster management operations such as provisioning and resizing, intermittently over about 2 days; customer clusters and data were not affected
- Users affected
- MongoDB Atlas and Cloud Manager customers
- Region
- –
- Time to detect
- –
- Time to resolve
- –
Symptoms
On 7 October 2025 MongoDB reported a delay in the metric ingestion pipeline of MongoDB Atlas and Cloud Manager. Metrics in Atlas dashboards arrived late or went missing, Host Down alerts did not fire, and Atlas cluster management operations such as provisioning and resizing were delayed, while customer clusters themselves stayed healthy and available.
The first investigation found high resource usage on one shard of the internal database cluster that backs the Atlas and Cloud Manager monitoring systems. Further review showed that high-traffic collections on that cluster were not sharded and sat on that single shard, that queries such as full collection scans added load to it, and that a rollout of an updated internal software version raised resource use beyond what had been expected. The postmortem describes partial impact that came and went over approximately 2 days.
Root cause
Root cause Capacity exhaustion
- Trigger
- The rollout of an updated internal software version caused a temporary spike in resource demand on the internal database cluster.
Detection
–
Remediation
- Took corrective actions to stabilise the system and monitored their effect
- Implemented a fix and monitored the results until the incident was resolved
Action items
- Shard the collections with concentrated load to spread traffic over more nodes
- Optimise inefficient queries
- Provision additional infrastructure capacity for higher traffic
- Refine capacity planning to anticipate future load spikes, using metrics from this event
- Redesign software rollouts to account for the predictable rise in resource demand during a rollout
- Keep monitoring how the sharding and query changes resolve the hotspots
- Expand the detection of elevated load conditions for faster anomaly detection and response
Lessons
–
Sources
- https://status.mongodb.com/incidents/rdzgw5xds7gx · official-status · archived copy
Related cases
IL-0450Oracle RAC commits behind order APIs kept waiting over 0.1 s on log file sync while average host CPU had headroomToss Securities · 2026same root cause · shared Database
IL-0553CircleCI's orchestration database filled its transaction log volume, and no workflows or jobs started for 50 minutesCircleCI · 2026same root cause · shared Database
IL-0379InfluxDB Cloud queries in Azure West Europe slowed and timed out as storage pods fell behind and kept restartingInfluxData · 2026same root cause · shared Database
IL-0309Preset's RDS PostgreSQL 14.7 to 17.9 upgrade in US East 1 ran out of storage and took Superset down for six hoursPreset · 2026same root cause · shared Database
IL-0435Error rates rose as Aurora MySQL killed connections and declined queries to avoid OOM while load metrics stayed flatCyberAgent · 2026same root cause · shared Database
IL-0497Buttondown's database ran out of connections twice in one day and requests failed while health checks mostly passedButtondown · 2026same root cause · shared Database
IL-0288ZooKeeperWait rose to thousands of seconds on three redundant ClickHouse instances, degrading a CDN77 data pipelineCDN77 · 2026same root cause · shared Database
IL-0350Hosts in an IONOS TXL cluster lost connectivity when an InfiniBand fabric resweep failed on a full multicast tableIONOS Cloud · 2026same root cause · shared Database
IL-0305Replicas of one Intercom Vitess shard hit 100% CPU and fell up to 2.2 hours behind, serving stale inbox dataIntercom · 2026same root cause · shared Database
IL-0390PostHog US Cloud event ingestion slowed to delays of up to 2 days as writes to the Persons Postgres table stalledPostHog · 2025same root cause · shared Database
IL-0100PostHog's feature flags pods were packed onto Kubernetes nodes that were too small for their CPU requests, and CPU saturation above 90% caused three outages in ten days through Redis overload, connection pool exhaustion and slow queriesPostHog · 2025same root cause · shared Database
IL-0557Database transaction locks piled up on Storj's US1 satellite, and uploads and downloads failed with timeouts for 2 hoursStorj · 2025same root cause · shared Database
IL-0551Bitbucket Cloud's overloaded primary database failed over, and the website, API and Pipelines were slow for almost a dayAtlassian · 2025same root cause · shared Database
IL-0298Wikimedia edits failed for 38 minutes when sessionstore Cassandra nodes in both data centres crashed on full disksWikimedia Foundation · 2025same root cause · shared Database
IL-0312Gadget's main Postgres did not start again after a restart to raise max_connections, and the platform went downGadget · 2024same root cause · shared Database
IL-0544Wasabi's database cache stopped responding when its queueing service filled up, and S3 failed in all regionsWasabi · 2024same root cause · shared Database
IL-0447An every RDS for MySQL instance slowed badly when its gp2 EBS BurstBalance ran out and IOPS fell to the baselineevery · 2024same root cause · shared Database
IL-0375MongoDB Atlas cluster changes and alerts lagged for hours after a control plane metadata migration congested a databaseMongoDB · 2024same root cause · shared Database
IL-0110A Grafana Agent pod's high memory use and crash-looping Hangfire pods drove a Kubernetes node into system OOM and NotReady, twice in one dayDFDS · 2024same root cause · shared Database
IL-0550Bitbucket Cloud's database slowed until connection pools saturated and requests timed out, leaving Pipelines pendingAtlassian · 2024same root cause · shared Database
IL-0270Discord's ScyllaDB authentication cluster overloaded during an OS upgrade, and logins failed for about 50 minutesDiscord · 2023same root cause · shared Database
IL-0202A burst of queries and database writes exhausted connection pools and memory on Honeycomb's ingest hosts, and Kubernetes crash-loop back-off kept failed hosts offline so ingest capacity stayed too low to recoverHoneycomb · 2023 · sev1same root cause · shared Database
IL-0386After a move to Google Cloud, Postgres connection timeouts and memcached i/o timeouts spiked on GKE nodesincident.io · 2023same root cause · shared Database
IL-0326A retention clean-up job filled the disk of MailPace's managed Postgres, which stayed offline for just over two hoursMailPace · 2023same root cause · shared Database
IL-0546Buildkite jobs could not go to newly connected agents once agent IDs passed a 32-bit integer foreign key's limitBuildkite · 2023same root cause · shared Database
IL-0500UToronto JupyterHub logins and server starts returned 500 errors when the hub's sqlite database disk filled up2i2c · 2022same root cause · shared Database
IL-0301Basecamp 3's primary database went into total gridlock at the top of the hour and Basecamp 3 went down twice37signals · 2022same root cause · shared Database
IL-0206Consul agents in GitLab.com's GKE pods were repeatedly OOM-killed, so the Rails pods lost database replica discovery and sent every query to the primaryGitLab · 2022same root cause · shared Database
IL-0302Peak load on GitHub's mysql1 MySQL cluster maxed out its database proxy's connections and stopped writes in March 2022GitHub · 2022same root cause · shared Database
IL-0212Many Slack users could not connect because a Vitess keyspace for channel membership was overloaded by cache-miss queriesSlack · 2022same root cause · shared Database
IL-0456Inflearn went down six times during a January 2022 free-course event as slow queries piled up on Aurora PostgreSQLInflab · 2022same root cause · shared Database
IL-0321GCP snapshots on all Patroni nodes stalled GitLab.com's primary PostgreSQL disk, Patroni failed over and 5xx spikedGitLab · 2021same root cause · shared Database
IL-0496Ably's Cassandra hit 100% CPU in every region and queries timed out globally, and the load returned on two more eveningsAbly · 2020same root cause · shared Database
IL-0443A Repro Aurora MySQL reader restarted unexpectedly and writer insert latency rose about sevenfold for a day or moreRepro · 2019same root cause · shared Database
IL-0037Image registry rate-limited a whole region after a crash-looping DaemonSet with imagePullPolicy Always pulled through three NAT instancesDatadog · 2019same root cause · shared Database
IL-0297Mezmo users could not sign in and log indexing lagged after the auth cache's Redis servers were OOM killedMezmo · 2019same root cause · shared Database
IL-0211A Mandrill PostgreSQL shard shut down at transaction ID wraparound and email sending was impaired for about 40 hoursMailchimp · 2019same root cause · shared Database
IL-0064CPU-heavy pods packed onto one Google Cloud node drove it to kernel panics, and the crash moved from node to node until the site was downMoonlight · 2019same root cause · shared Database
IL-0300Basecamp 3 went read-only for almost five hours when its events table reached the ceiling of 2,147,483,64737signals · 2018same root cause · shared Database
IL-0334Instapaper's RDS MySQL bookmarks table hit the 2TB ext3 file size limit, inserts failed and the service went downInstapaper · 2017same root cause · shared Database
IL-0333A downsized RDS PostgreSQL database maxed out its CPU at US peak and failing ELB health checks took buildkite.com downBuildkite · 2016same root cause · shared Database
IL-0282DynamoDB in US-East reached about 55% request errors as storage servers overloaded its metadata serviceAmazon Web Services · 2015same root cause · shared Database
IL-0383PagerDuty's shared Cassandra cluster degraded during a repair, delaying notifications and losing incoming eventsPagerDuty · 2014 · sev1same root cause · shared Database
IL-0320Postmark's primary MySQL disk filled but MySQL kept running, so MySQL-MMM never failed over and sending was delayedPostmark · 2011same root cause · shared Database
Check your cluster for this
For AI tools and scripts
- This case as JSON: https://incidentlib-api.benchlet.com/cases/IL-0287
- The cases most like it: https://incidentlib-api.benchlet.com/cases/IL-0287/similar
- MCP server (Streamable HTTP, no key):
https://incidentlib-mcp.benchlet.com/mcp
The API needs no key. The MCP server offers search_incidents, get_incident, list_incidents, get_topic and vocab; both are explained on API and MCP.