[SERVER-38940] Batch update fails with BSON error - MongoDB

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Not sure how to create a proper reproduction as I only face the issue at one very specific collection. I think it might be similar to https://jira.mongodb.org/browse/SERVER-32372 though.

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Not sure how to create a proper reproduction as I only face the issue at one very specific collection. I think it might be similar to https://jira.mongodb.org/browse/SERVER-32372 though.

When executing a batch update for one of our collections(5806 docs) we suddenly get a:

error: MongoError: BSONObj size: 16797454 (0x1004F0E) is invalid. Size must be between 0 and 16793600(16MB) First element: update: "collection_name"

using the node native driver at 3.1.10 on latest mongo 4.0 series @atlas

const bulk = db.collection(coll).initializeUnorderedBulkOp()

docs.forEach((\{query, update}) => bulk.find(query).updateOne(update)

bulk.execute()

While I managed to work around this issue by using manually decreasing the batch size via

let bulk = db.collection(coll).initializeUnorderedBulkOp();

let counter = 0;

for (const \{query, update} of docs) {

  bulk.find(query).updateOne(update);

  counter++;

  if ( counter % 500 == 0 ) {

    bulk.execute();

    counter = 0;

    bulk = db.collection(coll).initializeUnorderedBulkOp();

as i get the docs this should be handled internally.

is caused by

NODE-1778 BulkWrite: Incorrect batch-size calculations causes batch to fail