Operating System Support for Database Management Andrew Gladstone CSC 8410 3/26/2007 Background Based on 1981 Stonebraker paper Examine OS services as applicable to database use UNIX used as example OS
INGRES used as example DBMS OS Services Buffer Pool Management File System Scheduling / Process Management Consistency 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 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
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? 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
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? Scheduling / Process Mgmt. Two methods proposed Process / user, shared
code / data Single process server Requires DBMS scheduling service 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??? Consistency Control OS lock / protection on file - not record level Update order not guaranteed Buffer management / crash-recovery / locking managed by one system
Summary OS provided services too slow or inappropriate Most services provided by DBMS Double-effort results in considerable overhead
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