Creating a Schema

Precautions

• When you create a schema, select only data nodes that are in the same VPC as the DDM instance and are not used by other DDM instances. DDM will create databases on the selected data nodes without affecting their existing databases and tables.
• All instances associated with one schema must be of the same major MySQL version.
• Specifications of associated data nodes should be greater than that of the DDM instance. Otherwise the performance will be affected.
• Multiple schemas can be created in a DDM instance and associated with the same data node.
• One data node cannot be associated with schemas in different DDM instances.
• If you create a sharded schema, more than one shard will be generated in the schema. Shard names will follow the rule: <schemaname>_<number>. <number> here indicates a four-digit number starting from 0000. This number will be incremented by one. For example, if a schema name is db_cbb5 and there are 2 shards, the shard names are db_cbb5_0000 and db_cbb5_0001.
• Read-only instances cannot be associated with the schema as data nodes.
• Do not modify or delete the internal accounts (DDMRW*, DDMR*, and DDMREP*) created on data nodes. Otherwise, services will be affected.
  

  • The internal account name is in the format: Fixed prefix (such as DDMRW, DDMR, or DDMREP) + Hash value of the data node ID.
  • A random password is generated, which can contain 16 to 32 characters.

Prerequisites

• You have created a DDM instance and the instance is in the Available state.
• You have created an account. For details, see Creating an Account.

Procedure

1. Log in to the DDM console.
2. On the Instances page, locate the required DDM instance and click Create Schema in the Operation column.
   Figure 1 Creating a schema — Instances page
   

   Alternatively, click the instance name to go to the Basic Information page. On the displayed page, choose Schemas in the navigation pane and click Create Schema in the upper left corner of the page.

   Figure 2 Creating a schema — Schemas page
   

3. On the displayed page, configure required parameters.
   Figure 3 Creating a schema
   

   Table 1 Parameter description

   Parameter	Description
   Sharding	Sharded: indicates that one schema can be associated with multiple data nodes, and all shards will be evenly distributed across the nodes. Unsharded: indicates that one schema can be associated with only one data node, and only one shard can be created on the data node.
   Schema	The name can contain 2 to 48 characters and must start with a lowercase letter. Only lowercase letters, digits, and underscores (_) are allowed.
   Account	The DDM account that needs to be associated with the schema.
   Data Nodes	Select only data nodes that are in the same VPC as the DDM instance and are not used by other DDM instances. Databases can be created on the data nodes you select, without impacting existing databases and tables.
   Shards	The total shards are the shards on all data nodes. There cannot be more data nodes than there are shards in the schema. Each data node must have at least one shard assigned. Recommended shards per data node can be 8 to 64.

4. Click Next.
5. On the displayed page, enter a database account with the required permissions and click Test Availability.
   

   Required permissions: SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, RELOAD, PROCESS, REFERENCES, INDEX, ALTER, SHOW DATABASES, CREATE TEMPORARY TABLES, LOCK TABLES, EXECUTE, REPLICATION SLAVE, REPLICATION CLIENT, CREATE VIEW, SHOW VIEW, CREATE ROUTINE, ALTER ROUTINE, CREATE USER, EVENT, and TRIGGER WITH GRANT OPTION

   You can create a database account for the RDS for MySQL instance and assign it the above permissions in advance.

   Figure 4 Testing availability of data nodes
   

6. After the test becomes successful, click Finish.

   After the schema is created, the schema status is as follows:

   • Creating
   • Creation failed
   • Running