mongoDB : Building indexes in background

By default mongoDB build Indexes in foreground, it prevents all the read write operations to the database. When building an index on a collection, the database that holds the collection is unavailable for read or write operations until the index build completes.

Background index construction allows read and write operations to continue while building the index. Creation of background index takes more than foreground index.

How to perform indexing at background

While creating index, set the option “background” to true.

Example

> db.employee.ensureIndex({"firstName" : 1}, {"background":true})
{
        "createdCollectionAutomatically" : false,
        "numIndexesBefore" : 2,
        "numIndexesAfter" : 3,
        "ok" : 1
}

Note:

1. mongo shell session or connection where you are creating the index will block until the index build is complete. To continue issuing commands to the database, open another connection or mongo instance.

2. If MongoDB is building an index in the background, you cannot perform other administrative operations involving that collection.

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