DUMPTMIN parameter
Minimum free CCATEMP for DUMP
Summary
- Default value
- 0
- Parameter type
- System
- Where set
- System manager resettable
- Related products
- Fast/Backup
- Introduced
- Before Sirius Mods 6.7
Description
This parameter sets the minimum number of free CCATEMP pages that must be available for DUMP to use one for pre-imaging when waiting for second or subsequent tape volume mounts.
If a thread is performing an update on a file that is being dumped, and the thread needs to update a page that has not been dumped yet, that page needs to be dumped before the page can be updated. Normally, Fast/Backup will dump such a page almost immediately, and there will be no noticeable delay for the updating transaction. However, if Fast/Backup is waiting for a tape volume switch, perhaps waiting for a tape mount, an updating transaction in this scenario would also have to wait for the tape mount. The result is not good for the updating request, and potentially not good for other users in the Online, as resources held by the updating user are not released, and if sub-transaction checkpoints are being used, checkpoints are timed out.
In such a situation, Fast/Backup will try to copy the page to be updated to CCATEMP, allowing the updating thread to continue with its update. After the tape mount is satisfied, the page is copied from CCATEMP, and the CCATEMP used by the cached page is freed. Obviously, if there is a lot of updating for a file being dumped, and the dump ends up waiting on a tape mount, this could result in a lot of CCATEMP being used, leaving insufficient CCATEMP for other applications.
The DUMPTMIN parameter indicates the minimum number of CCATEMP pages that must be free, that is, available to other applications, before Fast/Backup will use one to cache a page that is about to be updated. If this number of pages is not available in the scenario described above, the updating thread will have to wait for the tape mount, or the dump will be terminated with an error, depending on the setting of the DUMPOPTS parameter.
The default value for DUMPTMIN of 0 means that no limit is placed on the use of CCATEMP pages by Fast/Backup.
See also DUMPTMAX.