# Common upgrade failures > Source-anchored research for Common upgrade failures. Run status: COMPLETED. Parent: [MongoDB Upgrade Paths](https://llms-explorer.com/tree/mongodb-upgrade-paths/) · 4 facets · 11 facts · page: https://llms-explorer.com/tree/common-upgrade-failures/ ## How it works - Custom MongoDB configuration settings can stop working when the target release changes its supported options. Percona's upgrade guide treats configuration review, hardware capacity, and application compatibility as distinct checks; a successful binary replacement alone does not validate those dependencies. (low confidence) — [source](https://learn.percona.com/hubfs/eBooks/Percona_Mongo-Upgrade_Best_Practices.pdf) ## Problems, failure modes and limitations - Percona's September 26, 2024 customer incident involved a sharded-cluster upgrade from MongoDB 5.0 to 6.0: data-bearing nodes upgraded successfully, but restarting mongos caused queries to fail with BSON field 'DatabaseVersion.timestamp' is missing but a required field. Refreshing each router's cached routing metadata with flushRouterConfig resolved the incident. (medium confidence) — [source](https://www.percona.com/blog/dealing-with-a-databaseversion-timestamp-error-after-a-mongodb-upgrade/) - Grafana's MongoDB plugin documentation says version 2.0.0 enforces maxTimeMS as a client-side deadline. Queries that previously returned partial results can instead fail with a timeout after that plugin upgrade. Attribute this specific failure to the integration's timeout behavior before calling it a MongoDB server regression. (low confidence) (verified as of 2026-10-23) — [source](https://grafana.com/docs/plugins/grafana-mongodb-datasource/latest/troubleshooting/?plcmt=products-nav) - MongoDB's engineering account describes cumulative small performance regressions and improvements that depend on the benchmark; its upgrade documentation explicitly says gains vary with workload and instance configuration. Published aggregate speedups therefore do not establish that an application's own workload cannot regress after an upgrade. (high confidence) — [source](https://www.mongodb.com/docs/manual/release-notes/8.0-upgrade-replica-set.md) ## Comparisons and alternatives - Comparing upgrade performance with different write-concern and journaling settings can confound diagnosis. Percona's 4.4-versus-7.0 write tests and MongoDB's engineering account both identify stronger default durability semantics as a contributor to additional write latency. (high confidence) — [source](https://www.percona.com/blog/mongodb-performance-regression-benchmarking-and-the-truth-behind-journaling/) - Percona's September 9, 2024 benchmark used a single-member replica set and reported large write-time reductions after weakening acknowledgement or journal-wait behavior. The author explicitly warned that disabling majority journal waiting can allow acknowledged operations to roll back after crashes affecting a majority. Such settings are a durability tradeoff, not a generally safe regression fix. (low confidence) — [source](https://www.percona.com/blog/mongodb-performance-regression-benchmarking-and-the-truth-behind-journaling/) - The upgrade guide warns that running setFeatureCompatibilityVersion while initial sync is in progress restarts that sync; AceMQ identifies the same operational trap. A longer-than-expected sync can therefore be caused by an administrative command rather than a new replication defect. (medium confidence) — [source](https://www.mongodb.com/docs/manual/release-notes/8.0-upgrade-replica-set.md) ## Facts and statements - Incompatible application drivers can leave an upgraded MongoDB deployment with unexpected behavior or application failures. Check the target server's driver compatibility and test the application against that target before production use. (high confidence) (verified as of 2026-10-09) — [source](https://www.mongodb.com/docs/manual/release-notes/8.0-upgrade-replica-set.md) - Successful startup does not rule out application latency regressions. Operators reported slower queries and timeouts after 6.0-to-7.0 upgrades, while MongoDB's engineers describe accumulated performance regressions across releases. These accounts justify workload-specific testing, not a claim that every upgrade slows queries. (medium confidence) — [source](https://www.mongodb.com/community/forums/t/performance-drop-after-upgrade-6-0-10-7-0-1/246712) - Meteor issue #14662, opened August 11, 2026, reports two concrete MongoDB bundle-build blockers: MongoDB 8.0.29 macOS archives unpacked to names with an extra hyphen, breaking a later mv command, and Meteor's custom Linux x86_64 download source lacked a version-8 archive. This is evidence about build tooling, not a production database corruption incident. (low confidence) (verified as of 2026-08-11) — [source](https://github.com/meteor/meteor/issues/14662) - Grafana documents that MongoDB-side version upgrades, Atlas tier changes, or replica-set reconfiguration can be followed by server-selection timeouts, ReplicaSetNoPrimary, or hostname-resolution failures. Its diagnostic guidance checks changed hostnames, the connection string, allowlists, and DNS SRV/TXT propagation; these symptoms alone do not establish data loss. (low confidence) (verified as of 2026-10-23) — [source](https://grafana.com/docs/plugins/grafana-mongodb-datasource/latest/troubleshooting/?plcmt=products-nav)