function repro() {

    db.c.drop()

    print("inserting")
    doc = {x: "x".repeat(1000)}
    many = Array(1000).fill(doc)
    for (var i = 0; i < 100; i++)
        db.c.insertMany(many)

    print("aggregating")
    r = db.c.aggregate([
        {
            $group: {
                "_id": "$_id",
                x: {$push: "$x"},
            }
        }
    ], {
        allowDiskUse: true
    })
}