Disk and File Summary (Contd.)
DBMS vs. OS File Support
- DBMS needs features not found in many OS’s, e.g., forcing a page to disk, controlling the order of page writes to disk, files spanning disks, ability to control pre-fetching and page replacement policy
File layer keeps track of pages in a file, and supports abstraction of a collection of records.
- Pages with free space identified using linked list or directory structure (similar to how pages in file are kept track of).
Many alternative file organizations exist, each appropriate in some situation.