Index là phương tiện rất mạnh để tăng hiệu năng thực hiện của câu lệnh. Bài giảng chương 10 này sẽ cung cấp một số kiến thức liên quan đến Indexing để người học có thể nắm bắt được những tiện ích của công cụ index trong CSDL. . | Chương 10: Indexing 1 Why Concerning Storage and Indexing? DB design using logical models (ER/Relational). Appropriate level for designers to begin with Provide independence from implementation details Performance: another major factor in user satisfaction Depends on Efficient data structures for data representation Efficiency of system operation on those structures Disks contains data files and system files including dictionary and index files Disk access: one of the most critical factor in performance. 2 Subjects to be Discussed Disks: Can retrieve random page, but reading several consecutive pages is much cheaper than reading them in random order Buffer manager: Stages pages from external storage to main memory buffer pool. File and index layers make calls to the buffer manager. File organization: Method of arranging a file of records on external storage. Record id (rid) is sufficient to physically locate record Indexes are data structures that allow us to find the record ids of . | Chương 10: Indexing 1 Why Concerning Storage and Indexing? DB design using logical models (ER/Relational). Appropriate level for designers to begin with Provide independence from implementation details Performance: another major factor in user satisfaction Depends on Efficient data structures for data representation Efficiency of system operation on those structures Disks contains data files and system files including dictionary and index files Disk access: one of the most critical factor in performance. 2 Subjects to be Discussed Disks: Can retrieve random page, but reading several consecutive pages is much cheaper than reading them in random order Buffer manager: Stages pages from external storage to main memory buffer pool. File and index layers make calls to the buffer manager. File organization: Method of arranging a file of records on external storage. Record id (rid) is sufficient to physically locate record Indexes are data structures that allow us to find the record ids of records with given values in index search key fields 3 Storage Hierarchy DBMS stores information on some storage medium Primary storage: can be operated directly by CPU. Secondary storage: larger capacity, lower cost, slower access cannot be operated directly by CPU – must be copied to primary storage Secondary storage has major implications for DBMS design READ: transfer data to main memory WRITE: transfer data from main memory. Both transfers are high-cost operations, relative to in-memory operations, so must be planned carefully 4 Why Not Store Everything in Main Memory? Cost and size Main memory is volatile: What’s the problem? Typical storage hierarchy: Factors: access speed, cost per unit, reliability Cache and main memory (RAM) for currently used data: fast but costly Flash memory: limited number of writes (and slow), non-volatile, disk-substitute in embedded systems Disk for the main database (secondary storage). Tapes for archiving older versions of the data (tertiary storage).
