Index Storage Cost
Parent: MongoDB Atlas Cost Optimization · Published reference · snapshot 2026-10-15
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Depth-first rabbithole dossier for Index Storage Cost; source-anchored research pack.
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Measurements and reference values
- [low] In one case study, the largest collection held about 300M documents using 130GB, with indexes accounting for another 30GB; after a data retention policy it fell to about 70M documents using less than 40GB plus 21GB of indexes. (verified as of 2026-10-15) Sources: https://dev.to/dlondero/saving-70-000-a-year-on-atlas-mongodb-534m [source]
Problems, failure modes and limitations
- [low] Unused indexes in MongoDB consume storage and slow down writes without delivering value. Sources: https://www.mongodb.com/docs/atlas/architecture/current/cost-saving-config.md [source]
- [low] An index can reach the two billion document limit. Sources: https://www.mongodb.com/docs/atlas/architecture/current/cost-saving-config.md [source]
Facts and statements
- [low] The MongoDB Performance Advisor suggests dropping unused, redundant, and hidden indexes to improve write performance and increase storage space. Sources: https://www.mongodb.com/docs/atlas/performance-advisor/drop-indexes.md [source]
- [low] MongoDB Atlas does not use hidden indexes to support queries, but they still impact write performance and consume storage space. Sources: https://www.mongodb.com/docs/atlas/performance-advisor/drop-indexes.md [source]
- [low] The Performance Advisor flags an index as unused if it has not supported a query in 7 or more days after creation or server restart, inspecting only the 20 most active collections. Sources: https://www.mongodb.com/docs/atlas/performance-advisor/drop-indexes.md [source]
- [low] The Performance Advisor flags an index as redundant if it matches the prefix of another index in the same collection. Sources: https://www.mongodb.com/docs/atlas/performance-advisor/drop-indexes.md [source]
- [low] The Performance Advisor always recommends dropping hidden indexes, which are displayed on the Atlas Performance Advisor page from the top 20 most active namespaces at page load. Sources: https://www.mongodb.com/docs/atlas/performance-advisor/drop-indexes.md [source]
Related concepts
- Index — is a part of Index Storage Cost
- Storage — is a part of Index Storage Cost
Children
- No children recorded.