create¶

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Definition
Considerations
Examples

Definition¶

create¶

Explicitly creates a collection. create has the following form:

{
  create: <collection_name>,
  capped: <true|false>,
  autoIndexId: <true|false>,
  size: <max_size>,
  max: <max_documents>,
  flags: <0|1|2|3>,
  storageEngine: <document>
}

create has the following fields:

Field	Type	Description
`create`	string	The name of the new collection.
`capped`	boolean	Optional. To create a capped collection, specify `true`. If you specify `true`, you must also set a maximum size in the `size` field.
`autoIndexId`	boolean	Optional. Specify `false` to disable the automatic creation of an index on the `_id` field. Important For replica sets, all collections must have `autoIndexId` set to `true`.
`size`	integer	Optional. Specify a maximum size in bytes for a capped collection. Once a capped collection reaches its maximum size, MongoDB removes the older documents to make space for the new documents. The `size` field is required for capped collections and ignored for other collections.
`max`	integer	Optional. The maximum number of documents allowed in the capped collection. The `size` limit takes precedence over this limit. If a capped collection reaches the `size` limit before it reaches the maximum number of documents, MongoDB removes old documents. If you prefer to use the `max` limit, ensure that the `size` limit, which is required for a capped collection, is sufficient to contain the maximum number of documents.
`flags`	integer	Optional. Available for the MMAPv1 storage engine only to set the `usePowerOf2Sizes` and the `noPadding` flags. To set, specify one of the following values: `0` corresponds to `usePowerOf2Sizes` flag set to `false` and `noPadding` flag set to `false`. `1` corresponds to `usePowerOf2Sizes` flag set to `true` and `noPadding` flag set to `false`. `2` corresponds to `usePowerOf2Sizes` flag set to `false` and `noPadding` flag set to `true`. `3` corresponds to `usePowerOf2Sizes` flag set to `true` and `noPadding` flag set to `true`. Note MongoDB 3.0 ignores the `usePowerOf2Sizes` flag. See `collMod` and `db.createCollection()` for more information. Defaults to `1`. New in version 2.6. Changed in version 3.0.0: Add support for setting the new `noPadding` flag. Warning Do not set `noPadding` if the workload includes removes or any updates that may cause documents to grow. For more information, see No Padding Allocation Strategy.
`storageEngine`	document	Optional. Available for the WiredTiger storage engine only. New in version 3.0. Allows users to specify configuration to the storage engine on a per-collection basis when creating a collection. The value of the `storageEngine` option should take the following form: copy { <storage-engine-name>: <options> } Storage engine configuration specified when creating collections are validated and logged to the oplog during replication to support replica sets with members that use different storage engines.

The db.createCollection() method wraps the create command.

Considerations¶

The create command obtains a write lock on the affected database and will block other operations until it has completed. The write lock for this operation is typically short lived. However, allocations for large capped collections may take longer.

Examples¶

Create a Capped Collection¶

To create a capped collection limited to 64 kilobytes, issue the command in the following form:

copy

db.runCommand( { create: "collection", capped: true, size: 64 * 1024 } )

Specify Storage Engine Options¶

New in version 3.0.

You can specify collection-specific storage engine configuration options when you create a collection with db.createCollection(). Consider the following operation:

copy

db.runCommand( {
    create: "users",
    storageEngine: { wiredTiger: { configString: "<option>=<setting>" } }
} )

This operation creates a new collection named users with a specific configuration string that MongoDB will pass to the wiredTiger storage engine. See the WiredTiger documentation of collection level options for specific wiredTiger options.

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