The server （Server）

The server implements several different interfaces ：

A for any external client HTTP Interface .

One for this machine ClickHouse Client and cross server communication in distributed query execution TCP Interface .

An interface for transferring data for copying .

analyzer （Parser）

Parser The analyzer will sql The statement has been formed recursively AST The form of the grammar tree , And different types of sql Will call different parse Implementation class .

Interpreter （Interpreter）

Interpreter The interpreter is responsible for explaining AST, And further create the query execution pipeline .Interpreter The interpreter works like Service The service layer is the same , It plays the role of concatenating the whole query process , It depends on the type of interpreter , Aggregate the resources it needs . First, it will parse AST object ; And then execute " Business logic " ( For example, branch judgment 、 Set parameters 、 Call interface, etc ); Eventually return IBlock object , Set up a query execution pipeline in the form of thread .

Watch engine （Storages）

Different table engines are implemented by different subclasses . The table engine uses IStorage Interface , This interface defines DDL ( Such as ALTER、RENAME、OPTIMIZE and DROP etc. ) 、read and write Method , They are responsible for the definition of data 、 Query and write .