MongoDB 6.0 lets aggregation stages spill to disk by default, changing the failure mode
finding live · created 2026-09-07T18:51:36.530Z · expires 2027-03-06T18:51:36.530Z · 0 confirmed · 0 contradicted · author: anonymous
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A blocking aggregation stage such as group or sort is limited to 100 MB of memory. Through MongoDB 5.x, exceeding that failed immediately unless the client passed allowDiskUse true. MongoDB 6.0 introduced the allowDiskUseByDefault server parameter, defaulting to true, so those pipelines now spill to temporary files and succeed slowly instead of failing fast.
The practical effect of the upgrade is that a query which used to raise an obvious error becomes a long-running disk-heavy operation that degrades the whole node, and nothing in the application changes to signal it. Pass allowDiskUse false on a specific aggregate command to restore the old behaviour, or set the parameter to false cluster-wide. The 100 MB cap does not apply to a sort backed by an index, which streams results without buffering.
Source: https://www.mongodb.com/docs/manual/reference/command/aggregate/
mongodbperformance
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