Aggregation Pipeline Limits
Aggregation operations with the aggregate command have the following limitations.
Result Size Restrictions
The aggregate command can either return a cursor or store the results in a collection. Each document in the result set is subject to the 16 megabyte BSON Document Size limit. If any single document exceeds the BSON Document Size limit, the aggregation produces 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.
Number of Stages Restrictions
Changed in version 5.0: MongoDB 5.0 limits the number of aggregation pipeline stages allowed in a single pipeline to 1000.
Memory Restrictions
Starting in MongoDB 6.0, the allowDiskUseByDefault parameter controls whether pipeline stages that require more than 100 megabytes of memory to execute write temporary files to disk by default.
-
If
allowDiskUseByDefaultis set totrue, pipeline stages that require more than 100 megabytes of memory to execute write temporary files to disk by default. You can disable writing temporary files to disk for specificfindoraggregatecommands using the{ allowDiskUse: false }option. -
If
allowDiskUseByDefaultis set tofalse, pipeline stages that require more than 100 megabytes of memory to execute raise an error by default. You can enable writing temporary files to disk for specificfindoraggregateusing the{ allowDiskUse: true }option.
The $search aggregation stage is not restricted to 100 megabytes of RAM because it runs in a separate process.
Examples of stages that can write temporary files to disk when allowDiskUse is true are:
-
$sortwhen the sort operation is not supported by an index
Note
Pipeline stages operate on streams of documents with each pipeline stage taking in documents, processing them, and then outputing the resulting documents.
Some stages can't output any documents until they have processed all incoming documents. These pipeline stages must keep their stage output in RAM until all incoming documents are processed. As a result, these pipeline stages may require more space than the 100 MB limit.
If the results of one of your $sort pipeline stages exceed the limit, consider adding a $limit stage.
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.