statements or translates the client commands written in programming languages 

like Perl or C++ into SQL statements. The embedded DML precompiler is 

responsible for translating requests into a format that MySQL understands.

The 

Query Processor

analyses the SQL statements from the embedded DML 

precompiler or user interface, and creates a parse tree structure to validate the 

SQL query syntax.

If the query is deemed to be valid, the Query Processor then performs the 

security checking. It checks the access permissions and makes sure that tables 

and records are accessed only by the authorized users.

After security checking, the query is analyzed and optimized in order to raise 

performance of the query process. The MySQL optimizer uses the most 

restrictive index first in order to eliminate as many rows as possible to proceed 

with less restrictive index optimization.

The last step in query processing is the execution of the SQL statement in the 

Execution Engine

.

 Specific tasks such as repair, backup, and recovery, which 

are started by the database administrator and processed from the DDL compiler 

are executed in the execution engine.

Transaction management

The 

Transaction Manager 

is responsible for making sure that transactions are 

logged and executed automatically in a safe and stable way. Resolving deadlock 

situations and issuing the commit or roll back commands to ensure database 

stability are done through the aid of the 

Log Manager and Concurrency 

Manager

. 

The 

Concurrency Control Manager 

ensures that transactions are executed 

separately and independently by acquiring locks from the locking table, on 

appropriate data in the database from the Resource Manager. Once the lock is 

acquired, only operations in one transaction can manipulate the data. If a 

different transaction tries to manipulate the same data, the request is rejected by 

the Concurrency Control Manager until the first transaction is complete.

Recovery management

The 

Log Manager

 is the module that is responsible for logging the operations 

executed in the database. The log is stored on the disk. In case of a system 

crash, executing each command in the log will bring the database back to its last 

stable state. This is done by the 

Recovery Manager

.

Resource Management

The Resource Management is responsible for memory allocation and retrieving 

data from physical disks, and writing data to physical disks.

 Chapter 1. Introduction 

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