Sharding #
Sharding Key #
Column used to determine database (table) sharding. For example, in last number modulo of order ID sharding, order ID is taken as the sharding key. The full route executed when there is no sharding column in SQL has a poor performance. Besides single sharding column, Apache ShardingSphere also supports multiple sharding columns.
Sharding Algorithm #
Data sharding can be achieved by sharding algorithms through =, >=, <=, >, <, BETWEEN and IN.
It can be implemented by developers themselves, or using built-in syntactic sugar of Apache ShardingSphere, with high flexibility.
Auto Sharding Algorithm #
It provides syntactic sugar for sharding algorithm. It used to manage all data nodes automatically, users do not care about the topology of physical data nodes. It includes lots of implementation for Mod, Hash, Range and Time Interval etc.
User-Defined Sharding Algorithm #
It provides interfaces for developers to implement the sharding algorithm related to business implementation, and allows users to manage the physical topology physical data nodes by themselves. It includes:
- Standard Sharding Algorithm
It processes the sharding case in which single sharding keys =, IN, BETWEEN AND, >, <, >=, <= are used.
- Complex Keys Sharding Algorithm
It processes the sharding case in which multiple sharding keys are used. It has a relatively complex logic that requires developers to deal by themselves.
- Hint Sharding Algorithm
It processes the sharding case in which Hint is used.
Sharding Strategy #
It includes the sharding key and the sharding algorithm, and the latter one is extracted out for its independence. Only sharding key + sharding algorithm can be used in sharding operation.
SQL Hint #
In the case that the sharding column is not decide by SQL but other external conditions, SQL hint can be used to inject sharding value. For example, databases are sharded according to the staff’s ID, but column does not exist in the database. SQL Hint can be used by two ways, Java API and SQL comment (TODO). Please refer to Hint for more details.