Mongodb update with upsert fails

Question

Here is the statement which fails:

db.some_collection.update(query,modifier_set, upsert=True, safe=True)

modifier_set is of the form {"$inc":{...}, "$addToSet":{...}}

I get an OperationFailure error:

$ operator made object too large

Now, it's highly unlikely that my document it more that 16MB.

Any other possible reasons for such failure ?

Answer 1

It is actually a case of oversized document.
db.collection_name.stats() confirmed it.