Feature Compatibility Version

You cannot copy data between a mongod instance with featureCompatibilityVersion (FCV) 3.6 and a MongoDB version 3.4 and earlier mongod instance.

For example:

Operations that copy data include:

• db.cloneCollection() and the command cloneCollection
• db.cloneDatabase() and the command clone
• db.copyDatabase() and the command copydb

Destination

• Run db.copyDatabase() in the admin database of the destination mongod instance, i.e. the instance receiving the copied data.
• db.copyDatabase() creates the target database if it does not exist.
• If the target database exists and no collection from the source database exists in the target database, db.copyDatabase() copies the collections from the source database to the target database. If any collection from the source database exists in the target database, db.copyDatabase() errors out and does not copy any remaining collections from the source database.
• db.copyDatabase() requires enough free disk space on the host instance for the copied database. Use the db.stats() operation to check the size of the database on the source mongod instance.

Authentication to Source mongod Instance

• If copying from another mongod instance (fromhost) that enforces access control, then you must authenticate to the fromhost instance by specifying the username, password, and optionally mechanism. The method does not transmit the password in plaintext.

  When authenticating to the fromhost instance, db.copyDatabase() uses the fromdb as the authentication database for the specified user.

• When authenticating to the fromhost instance, db.copyDatabase() supports SCRAM-SHA-1 and MONGODB-CR mechanisms to authenticate the fromhost user.

  • To authenticate to a version 2.6 fromhost, you must specify MONGODB-CR as the authentication mechanism. See Copy Database from a mongod Instances that Enforce Authentication.
  • To copy from a version 3.0 fromhost to a version 2.6 instance, i.e. if running the method from a version 2.6 instance to copy from a version 3.0 fromhost, you can only authenticate to the fromhost as a MONGODB-CR user.

For more information on required access and authentication, see Required Access.

Concurrency

• db.copyDatabase() and clone do not produce point-in-time snapshots of the source database. Write traffic to the source or destination database during the copy process will result in divergent data sets.
• db.copyDatabase() does not lock the destination server during its operation, so the copy will occasionally yield to allow other operations to complete.

Indexes

MongoDB performs foreground builds of indexes on databases copied via db.copyDatabase(). Foreground index builds lock the database and prevent all other operations on that database until the foreground build completes. There may also be a performance impact on other databases while the indexes build.

You can keep track of ongoing index creation operations with the db.currentOp() command.

Sharded Clusters

• Do not use db.copyDatabase() from a mongos instance.
• Do not use db.copyDatabase() to copy databases that contain sharded collections.

Changed in version 2.6.

Source Database (fromdb)

If the mongod instance of the source database (fromdb) enforces access control, you must have proper authorization for the source database.

If copying from another mongod instance (fromhost) that enforces access control, then you must authenticate to the fromhost instance by specifying the username, password, and optionally mechanism. The method does not transmit the password in plaintext.

When authenticating to the fromhost instance, db.copyDatabase() uses the fromdb as the authentication database for the specified user.

When authenticating to the fromhost instance, db.copyDatabase() supports SCRAM-SHA-1 and MONGODB-CR mechanisms to authenticate the fromhost user.

• To authenticate to a version 2.6 fromhost, you must specify MONGODB-CR as the authentication mechanism. See Copy Database from a mongod Instances that Enforce Authentication.
• To copy from a version 3.0 fromhost to a version 2.6 instance, i.e. if running the method from a version 2.6 instance to copy from a version 3.0 fromhost, you can only authenticate to the fromhost as a MONGODB-CR user.

{ resource: { db: "mySourceDB", collection: "" }, actions: [ "find", "listCollections", "listIndexes" ] },
{ resource: { db: "mySourceDB", collection: "system.js" }, actions: [ "find" ] },

{ resource: { db: "admin", collection: "" }, actions: [ "find",  "listCollections", "listIndexes" ]