PHP Manual

Creating An Index

MongoDB supports indexes, and they are very easy to add on a collection. To create an index, you specify the field name and direction: ascending (1) or descending (-1). The following creates an ascending index on the "i" field:

= new MongoClient();
$collection $connection->database->collectionName;

$collection->ensureIndex( array( "i" => ) );  // create index on "i"
$collection->ensureIndex( array( "i" => -1"j" => ) );  // index on "i" descending, "j" ascending

Indexing is critical for good read performance as your data grows. If you are not familiar with indexing, check out the MongoCollection::ensureIndex() documentation and the core » MongoDB indexing documentation.

PHP Manual