1. Operating System Support for Database Management Andrew Gladstone CSC 8410 3/26/2007

2. Background Based on 1981 Stonebraker paper Examine OS services as applicable to database use UNIX used as example OS INGRES used as example DBMS

3. OS Services Buffer Pool Management File System Scheduling / Process Management Consistency

4. Buffer Management UNIX provisions:  Fixed-size buffer pool  Size set upon compilation  I/O handled through main-memory cache  LRU replacement strategy for misses  Block-prefetch for sequential access

5. Deficiencies Fetch performance Suboptimal replacement strategy  Access Types: Sequential access one time Sequential access cyclically re-referenced Random access one time Random access possible rereference Inefficient prefetch

6. Solutions? DBMS managed buffer pool Composite replacement strategy  Database access in INGRES: Sequential access (no re-reference) : toss immediately Sequential access (cyclical re-reference): MRU Random access (no re-reference): toss immediately Random access (potential re-reference): LRU Prefetch?

7. Crash Recovery Implemented by the DBMS “Intentions List” and “Commit Flag” Requires OS to perform “selected force out” Critical to ensure accurate post-crash writes / rollbacks

8. Summary (not displayed) As of the writing, no OS exists with a buffer manager that has the required features to provide efficient service for a DBMS. Most DBMS employ a strategy of maintaining a separate cache in the user-space, managed by the DBMS specific algorithm. So the OS service is wasted when the DBMS is running. Also mention that DBMS

9. File System Character Arrays Designed for sequential access  DBMS data generally not sequential No record management service Two OS trees + one DBMS tree  Why not one tree?

10. Scheduling / Process Mgmt. Two methods proposed  Process / user, shared code / data Single process server  Requires DBMS scheduling service

11. Scheduling Challenges Separate Processes  Memory requirements  Task switching  Relies on OS message-passing system Server Model  DBMS must manage scheduling and m/t  “Mini OS” running in user-space “Favored-user” class???

12. Consistency Control OS lock / protection on file - not record level Update order not guaranteed Buffer management / crash-recovery / locking managed by one system

13. Summary OS provided services too slow or inappropriate Most services provided by DBMS Double-effort results in considerable overhead