public MongoCursor MongoCursor::batchSize ( int
MongoCursor::batchSize — Limits the number of elements returned in one batch
The number of results to return per batch. Each batch requires a round-trip to the server.
batchSizeis 2 or more, it represents the size of each batch of objects retrieved. It can be adjusted to optimize performance and limit data transfer.
batchSizeis 1 or negative, it will limit of number returned documents to the absolute value of batchSize, and the cursor will be closed. For example if batchSize is -10, then the server will return a maximum of 10 documents and as many as can fit in 4MB, then close the cursor.Внимание
batchSizeof 1 is special, and means the same as -1, i.e. a value of 1 makes the cursor only capable of returning one document.
Note that this feature is different from MongoCursor::limit() in that documents must fit within a maximum size, and it removes the need to send a request to close the cursor server-side. The batch size can be changed even after a cursor is iterated, in which case the setting will apply on the next batch retrieval.
This cannot override MongoDB's limit on the amount of data it will return to the client (i.e., if you set batch size to 1,000,000,000, MongoDB will still only return 4-16MB of results per batch).
To ensure consistent behavior, the rules of MongoCursor::batchSize() and MongoCursor::limit() behave a little complex but work "as expected". The rules are: hard limits override soft limits with preference given to MongoCursor::limit() over MongoCursor::batchSize(). After that, whichever is set and lower than the other will take precedence. See below. section for some examples.