cloneCollectionAsCapped¶

Definition定义¶

cloneCollectionAsCapped¶

The cloneCollectionAsCapped command creates a new capped collection from an existing, non-capped collection within the same database. The operation does not affect the original non-capped collection.

The command has the following syntax:语法如下所示：

{ cloneCollectionAsCapped: <existing collection>,
  toCollection: <capped collection>,
  size: <capped size>,
  writeConcern: <document>,
  comment: <any>
}

The command takes the following fields:

Field字段	Description描述
cloneCollectionAsCapped	The name of the existing collection to copy.
toCollection	The name of the new capped collection to create. The name of the new capped collection must be distinct and cannot be the same as that of the original existing collection.
size	The maximum size,in bytes, for the capped collection.
writeConcern	Optional.可选。A document expressing the write concern of the drop command. Omit to use the default write concern.
comment	Optional.可选。A user-provided comment to attach to this command. Once set, this comment appears alongside records of this command in the following locations: mongod log messages, in the attr.command.cursor.comment field. Database profiler output, in the command.comment field. currentOp output, in the command.comment field. A comment can be any valid BSON type (string, integer, object, array, etc). New in version 4.4.版本4.4中的新功能。

The command copies an existing collection and creates a new capped collection with a maximum size specified by the capped size in bytes.

To replace the original non-capped collection with a capped collection, use the convertToCapped command.

Behavior行为¶

If the capped size is less than the size of the source collection, then not all documents in the source collection will exist in the destination capped collection.

This holds a database exclusive lock for the duration of the operation. Other operations which lock the same database will be blocked until the operation completes. See What locks are taken by some common client operations? for operations that lock the database.