MongoError: document constructed by $facet is 104860008 bytes, which exceeds the limit of 104857600 bytes

user_3975029 0
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I am getting memory size limit error while running multiple sub-pipelines in $facet. Can someone help me on this issue. Scenario: I have a crown job which runs once a day. I want to execute multiple pipelines using $facet against a collection with millions of documents whenever job is triggered.

[ 
     {
          $facet: {
                  query1: [pipeline_1],
                  query2: [pipeline_2],
                  query3: [pipeline_3]
                  ...
                  query_n: [pipeline_n]
          },
     },
     {
        $merge:{ into: some_collection}
     }
]

I tried db.collection.aggregate([], {allowDiskUse: true});, But still getting same error. What can be the work around on this. Please help.

aggregation-framework mongodb
1 Answers

In most cases using allowDiskUse should eliminate this error this is why i'm suspecting you're using the wrong syntax for it. Depending on your Mongo version there are some hard limitations on certain operators like $graphLookup, these operators will always have a memory error regardless of the allowDiskUse flag usage.

Assuming you don't use any of these operators allowDiskUse will work, here is a syntax example for the nodejs driver:

db.collection.aggregate([], {allowDiskUse: true});

If you are $graphLookup or one of the other limited operators then there's not much you can do. I would start by splitting these $facet stages into separate pipelines. If the problem still persists you'll need to either optimize the aggregation or find a different approach.

user_107703700
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