(PECL mongo >=1.0.11)
MongoCursor::batchSize — Limits the number of elements returned in one batch
A cursor typically fetches a batch of result objects and store them locally. This method sets the batchSize value to configure the amount of documents retrieved from the server in one round trip. However, it will never return more documents than fit in the max batch size limit (usually 4MB).
batchSize
The number of results to return per batch. Each batch requires a round-trip to the server.
If batchSize is 2 or
more, it represents the size of each batch of objects retrieved.
It can be adjusted to optimize performance and limit data transfer.
If batchSize is 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.
A batchSize of 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.
Returns this cursor.
Example #1 MongoCursor::batchSize() and combinations with MongoCursor::limit()
<?php
// one batch, at most 10 items. The -10 makes the server to return 10 items,
// and then remove the cursor.
$cursor->limit(20)->batchSize(-10);
// first batch: at most 10 items
$cursor->limit(10);
// first batch: at most 10 items
$cursor->limit(10)->batchSize(20);
// results are fetched in batches of 10 each, with a maximum of 20 items
// returned (that means two batches of 10).
$cursor->limit(20)->batchSize(10);
// results are fetched in batches of 7 each, with a maximum of 30 items
// returned (that means that the driver requests 4 batches of 7, and one batch
// of 2).
$cursor->limit(30)->batchSize(7)
?>
MongoDB core docs on » batchSize.
| 版本 | 说明 |
|---|---|
| 1.4.5 |
Before 1.4.5, this method would throw an MongoCursorException if the cursor had already started iterating. |