The major sharding processes of all the three Sharding-Sphere products are identical. The core is consist of SQL parsing => query optimization => SQL route => SQL rewrite => SQL execution => result merger.
It is divided into lexical parser and syntactic parser. The lexical parser will separate SQL into inseparable words, and then syntactic parser will understand SQL and extract the context. Tables, selecting items, ordering items, grouping items, aggregation functions, pagination information, query conditions and placeholders that may be revised are all included in the parsing context.
It merges and optimizes sharding conditions, such as OR.
It is the sharding strategy that matches users’ configurations according to the parsing context and generates route path. It supports sharding route and broadcast route currently.
It rewrites SQL as statement that can be rightly executed in the real database, and can be divided into correctness rewrite and optimization rewrite.
It executes asynchronously through multi-threading executor.
It merges multiple execution result sets to output through unified JDBC interface. Result merger includes methods as stream merger, memory merger and addition merger using decorator merger.