Kbase P18576: How does the OS time affect Progress Database?
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
05/11/2004 |
|
Status: Unverified
GOAL:
Can a database backup be restored on a system that date is before the production.
GOAL:
How does Operating System time affect the progress Database?
GOAL:
How will bringing the operating system back in time affect the database?
FIX:
Information taken from
Summertime in the Database
Engine Crew Monograph No. 11
In version 7.3A and later, the database manager generates time stamps slightly differently. If it notices that the system clock has gone backwards, instead of shutting down, it writes a message to the .lg file recording the error. Instead, the error is added to an "accumulated clock error" field kept internally and all bi cluster timestamps are adjusted by the accumulated error.
This allows the relative ages of clusters to be known correctly if the system clock is adjusted backwards. However, there will still be an error in the absolute cluster age. This may cause a cluster to be aged longer than needed. This will do no harm, but may result in temporary bi file growth.
If the clock is adjusted forward, the database manager does not know this and takes no special action since a new time stamp will be later than the old one. In this case, the relative ages of clusters is known correctly. But the absolute cluster age will be incorrect. A cluster may be aged prematurely and reused too soon. If the system crashes at this point (within a few minutes of the time change), crash recovery may not be possible.