create¶

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>
}

create has the following fields:

Field	Description
`create`	The name of the new collection.
`capped`	Optional. To create a capped collection. specify `true`. If you specify `true`, you must also set a maximum size in the `size` field.
`autoIndexId`	Optional. Specify `false` to disable the automatic creation of an index on the `_id` field. Before 2.2, the default value for `autoIndexId` was `false`.
`size`	Optional. The maximum size for the capped collection. Once a capped collection reaches its maximum size, MongoDB overwrites older old documents with new documents. The `size` field is required for capped collections.
`max`	Optional. The maximum number of documents to keep in the capped collection. The `size` limit takes precedence over this limit. If a capped collection reaches its maximum size before it reaches the maximum number of documents, MongoDB removes old documents. If you use this limit, ensure that the `size` limit is sufficient to contain the documents limit.
`flags`	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.

For more information on the autoIndexId field in versions before 2.2, see _id Fields and Indexes on Capped Collections.

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.

Example¶

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

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

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