Aggregation Pipeline Limits¶

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Result Size Restrictions
Memory Restrictions

Aggregation operations with the aggregate command have the following limitations.

Result Size Restrictions¶

Changed in version 3.6: MongoDB 3.6 removes the option for the aggregate command to return its results as a single document.

The aggregate command can return either a cursor or store the results in a collection. When returning a cursor or storing the results in a collection, each document in the result set is subject to the BSON Document Size limit, currently 16 megabytes; if any single document that exceeds the BSON Document Size limit, the command will produce an error. The limit only applies to the returned documents; during the pipeline processing, the documents may exceed this size. The db.collection.aggregate() method returns a cursor by default.

Memory Restrictions¶

Pipeline stages have a limit of 100 megabytes of RAM. If a stage exceeds this limit, MongoDB will produce an error. To allow for the handling of large datasets, use the allowDiskUse option to enable aggregation pipeline stages to write data to temporary files.

Changed in version 3.4.

The $graphLookup stage must stay within the 100 megabyte memory limit. If allowDiskUse: true is specified for the aggregate() operation, the $graphLookup stage ignores the option. If there are other stages in the aggregate() operation, allowDiskUse: true option is in effect for these other stages.

Starting in MongoDB 4.2, the profiler log messages and diagnostic log messages includes a usedDisk indicator if any aggregation stage wrote data to temporary files due to memory restrictions.