Query processor DATABASE SYSTEM STRUCTURE A Database system is partitioned into modules that deal with each of the responsibilities of the overall system. The functional components of a database system can be broadly divided into the storage manager and query processor components.
The Query Processor is important because it helps the database system simplify and facilitate access to data. High level views help to achieve this goal; with them, users of the system are not be burdened unnecessarily with the physical details of the implementation of the system. However, quick processing of updates and queries is important. It is the job of the database system to translate updates and queries is important. It is the job of the database system to translate updates and queries written in a nonprocedural language, at the logical level, into an efficient sequence of operations at the physical level. Storage Manager A storage manager is a program module that provides the interface between the low level data stored in the database and the application programs and queries submitted to the system. The storage manager is responsible for the interaction with the file manager. The raw data are stored on the disk using the file system, which is usually provided by a conventional operating system. The storage manager translates the various DML statements into low level file system commands. Thus, the storage manager is responsible for storing, retrieving and updating data in the database. The storage manager components include:
Which tests for the satisfaction of integrity constraints and checks the authority of users to access data.
Which ensures that the database remains in a consistent correct) state despite system failures, and that concurrent transaction executions proceed without conflicting.
Which manages the allocation of space on disk storage and the data structures used to represent information stored on disk.
Which is responsible for fetching data from disk storage into main memory, and deciding what data to cache in main memory. The buffer manager is a critical part of the database system, since it enables the database to handle data sizes that are much larger than the size of main memory. The storage manager implements several data structures as part of the physical system implementation:
The Query Processor The query processor components include
A query can usually be translated into any of a number of alternative evaluation plans that all give the same result. The DML compiler also performs query optimization, that is it picks the lowest cost evaluation plan from among the alternatives.
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