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DBMS Physical Design

DBMS Physical Design. Physical design is concerned with the placement of data and selection of access methods for efficiency and ongoing maintenance. File Organization. Physical arrangement of the records of a file on secondary storage devices. Sequential Linked List Indexed Hashed.

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DBMS Physical Design

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  1. DBMS Physical Design Physical design is concerned with the placement of data and selection of access methods for efficiency and ongoing maintenance

  2. File Organization Physical arrangement of the records of a file on secondary storage devices • Sequential • Linked List • Indexed • Hashed

  3. Sequential File Sequential file sorted in alphabetical order. Sequential files are usually sorted in ID sequence order to facilitate batch processing.

  4. Sequential File Processing Old Master New Master Process Transaction Sequential files must be recopied from the point of any insertion or deletion to the end of the file. They are commonly used in batch processing where a new master file will be generated each time the file is updated.

  5. Linked List Linked list to sort data alphabetically within department. An external reference must point to the start record (05).

  6. Linked List File Processing The next record in a linked list is found at the address stored in the record. Records are added at any location in the DASD and pointers adjusted to include them. Deletions are not erased, but pointers changed to omit the deleted record.

  7. Indexed File(sequential index) Index to access data by department abbreviation.

  8. Indexed File Processing Index Index Data File When a record is inserted or deleted in a file the data can be added at any location in the data file. Each index must also be updated to reflect the change. For a simple sequential index this may mean rewriting the index for each insertion.

  9. Segmented Index Index Root Nodes Leaf Data

  10. Indexed File Processing (segmented index) Index Data File Data can be inserted or deleted at any location in the data file. The index(es) must be updated for each change, but only the affected segments need to be rewritten.

  11. Physical Design • Volume and Usage analysis • Distribution Strategy • File Organizations • Indexes and Access Methods • Integrity Constraints

  12. Physical Design Issues • Size • Speed of access • Speed of update • Growth issues: performance and degradation • Security • Maintenance

  13. Relationships: physical address pointers Links generated when data is entered Efficient but not flexible Ad hoc design Query dependent on specific DBMS (may support SQL) Relationships: logical data references Links generated when data is retrieved Flexible but not efficient Theoretical base SQL DBMS Organization Structured Relational

  14. DBMS Technology • CPU • Components • Operation • DASD • Technology • Organization • Data Transfer • Access methods

  15. Physical DesignData Distribution • Centralized • Partitioned Horizontal Vertical • Replicated • Hybrid

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