Core Functions

**Table 1** DDM main functions
Function	Description
Horizontal sharding	Select a sharding key when creating a logical table. DDM will generate a sharding rule and horizontally shard data.
Flexible shard configuration	DDM supports both compute and storage scaling. You can add nodes to a DDM instance or scale up its node class. Alternatively, increase shards or data nodes to distribute data from one large table to multiple tables or scale out storage resources. Compute scaling is undetectable to your applications. Storage scaling minimizes service interruption to seconds.
Distributed transactions	DDM processes three types of transactions, including single-shard, FREE, and Extended Architecture (XA). Single-shard: Transactions cannot be committed across shards. FREE: Transactions are committed across shards. A transaction is not rolled back when it fails to be executed by any shard, causing data inconsistency. XA: Transactions are committed in two phases. If a transaction fails to be executed by any shard, all work done will be rolled back to ensure data consistency.
Data import and export	External data can be imported into DDM instances to help you migrate databases to the cloud, and DDM instance data can be exported based on service requirements.
Highly compatible SQL syntax	DDM is highly compatible with the MySQL licenses and syntax.
Read and write splitting	Read and write requests can be split without modifying the application code, and this is totally transparent to applications. You only need to create read replicas for a MySQL instance associated with your DDM instance and configure a read policy, and a large number of concurrent requests can read data from those read replicas.
Global sequence	DDM allows you to use globally unique, distributed, and ascending SNs as primary or unique keys or to meet your requirements in specific scenarios.
Online monitoring	DDM monitors reads, writes, and slow query logs of your DDM instance on the console, helping you detect resource and performance bottlenecks as fast as possible.
DDM console	The DDM console enables you to manage and maintain DDM instances, schemas, and accounts.