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.
If an aggregation pipeline exceeds the stage limit before or after being parsed, you receive an error.
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.
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.