When inserting a list of documents via DBCollection.insert( List<DBObject> list ), this List gets converted into an Array:

public WriteResult insert(List<DBObject> list) throws MongoException

{ return insert( list.toArray( new DBObject[list.size()] ) , getWriteConcern() ); }

Later on, when it gets to the real implementation of the insert in DBApiLayer.MyCollection.insert, each element of this array is inserted into BSONEncoder ( via OutMessage ). Further this array is never used.

So, it seems that there is no real benefit to convert the initial List into an Array. And for a performance sake, it should be left alone as a List.

For example, in my tests, for a 1,000,000 documents 665 bytes each, "list.toArray( new DBObject[list.size()] )" takes 40 milliseconds. While it may not seem like a lot, it all can add up given a bigger document size / more documents / etc.. And, unless I missed something, there is no good reason for this conversion in the first place.

/Anatoly