Kbase P134520: Why a query runs faster the second time even after the DB broker has been shut down ?
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
2/24/2010 |
|
Status: Verified
GOAL:
Why a query runs faster the second time even after the DB broker has been shut down ?
GOAL:
Effects of UNIX file system buffer pools and disk cache on DB queries.
FACT(s) (Environment):
UNIX
Progress 6.x
Progress 7.x
Progress 8.x
Progress 9.x
OpenEdge 10.x
FIX:
The UNIX file system cache is not cleared when the database is shutdown.
This explains the type of behavior - slow, fast, fast, when queries are performed, even after the DB has been stopped.
When database reads blocks from the file system they are read into shared memory, the operating system may deliver blocks from the file system cache and this will improve the performance.
Disks and storage subsystems have caches too, but they are rarely large enough to have large effects.
To clear the file system cache (for performance test purposes), unmount and remount the file system(s) that
have the database.