REPLICATE DATABASE

Starts or continues replicating a database from a remote host to the local host. The database on the remote host is the primary database and the database on the local host is its secondary. A database can be replicated either within a single cluster or to a different cluster. Typically, the primary database should be in a different cluster than the secondary database.

It is useful in maintaining database backups, high availability (HA) and disaster recovery (DR).

Note

You cannot use this command to replicate an unlimited storage database. For an alternative, see Replicate an Unlimited Storage Database.

Running this command with Kerberos authenticated users is not supported because the secondary cluster only talks to the primary cluster by authenticating with passwords.

Syntax

REPLICATE DATABASE db_name [WITH FORCE DIFFERENTIAL] FROM master_user[:'master_password']@master_host:master_port[/master_db_name]

Remarks

  • db_name is the name of the target database on the secondary SingleStore DB instance. REPLICATE DATABASE will attempt to create a new database named db_name, unless the WITH FORCE DIFFERENTIAL clause is used. The database name on the secondary does not need to match the name of its corresponding remote primary database.

  • REPLICATE DATABASE always replicates asynchronously.

  • If you run STOP REPLICATING, replication stops and the secondary database is promoted to the primary database on the local host. When replication stops, the promoted database will use synchronous replication, if the previous primary database used synchronous replication. Likewise, the promoted database will use asynchronous replication, if the previous primary database used asynchronous replication.

  • The following applies if the secondary database were to be promoted to the primary database on the local host: If the promoted database uses synchronous replication, the former primary database’s durability setting is used. If the promoted database uses asynchronous replication, asynchronous durability is used. (In-memory database updates you make using DDL and DML are durable when they are also saved to the log on disk). For more information, see Replication and Durability Concepts.

  • WITH FORCE DIFFERENTIAL replicates only the contents of the primary database that are not already in the secondary database. Most often, you should use the WITH FORCE DIFFERENTIAL clause to resume replication from the original primary database following a cluster failover. When you use this clause, a new database is not created, because the database already exists.

  • In case of multiple DR replications, if you run STOP REPLICATING for one replication, you cannot run the REPLICATE DATABASE WITH FORCE DIFFERENTIAL command for the other replications.

  • master_user should have relevant permissions. This user must have access to first do the resource check in the information schema in the primary database and then the initial replication setup. This user is only used to kickstart the replication, future replications will happen using internal SingleStore authentication negotiated during the REPLICATE handshake.  Hence this user need not exist after the REPLICATE command completes. You can switch to a different user to do the initial setup in future replications without making any modifications to the existing replications.

  • master_password is assumed to be blank if it is not specified explicitly. If you specify a password, enclose it in single quotes.

  • master_host is the host name or IPv4/IPv6 pointing to the remote database. It can be quoted to allow special characters (e.g. -, among others). master_host can be in the same cluster or in a different cluster than the local host.

  • master_db_name is the name of the remote, primary database. If it is not specified explicitly, SingleStore DB attempts to replicate from db_name on the master SingleStore DB instance.

  • While replicating, the database is in the replicating state (see Database States).

  • The long form of CONTINUE REPLICATING can be used to re-point a replica from one master to another.

  • If the primary database contains pipelines, the state of these pipelines (such as the pipeline offsets) are replicated to the secondary database.

  • This command cannot be run on system databases.

Notice

Data is always replicated across clusters asynchronously. Databases are replicated at the leaf level, which implies that a leaf in the secondary cluster replicates data directly from a leaf in the primary cluster; therefore, when connecting a secondary cluster to the primary cluster, the leaves in the primary and secondary cluster must be able to communicate with each other. They should not be blocked by firewall or network rules.

Examples

Basic Usage

REPLICATE DATABASE ExampleDatabase FROM root@master-host:3306;

With Password

REPLICATE DATABASE ExampleDatabase FROM master_user:'master_password'@master-host:3306/MasterExampleDatabase;

Replicating Using WITH FORCE DIFFERENTIAL

The Replicating Data Across Clusters topic provides examples of using WITH FORCE DIFFERENTIAL to replicate only the contents of the primary database that are not already in the secondary database.

Related Topics