An Enhancement to the PROBKUP online routine in Progress 9.1E01 and OpenEdge 10.0B02 improves overall performance while the backup is running.
- Prior to this change, blocks already in the Buffer Pool at the time of an online PROBKUP are never moved to the Least Recently Used (LRU) end when the block version (and backup counter) is updated when it is included in the backup volume.
- With this change, if a buffer (to be backed up) already exists in the buffer pool at the LRU end, it is no longer moved from it's current position in the (LRU) chain to the Most Recently Used (MRU) end and the backup puts blocks that need to be read into shared-memory at the bottom of the LRU chain.
In addition, the PROBKUP online routine is enhancement , to allow it to make use of Private Read-Only Buffers (-Bp). This enhancement is in addition to the performance improvement mentioned above. In effect, rather than always holding all the buffers that need to be read at the LRU end of the chain of buffers in the buffer pool, when using -Bp, an online backup will use its own Private Buffer list.
When PROBKUP does not use Private Buffers (-Bp), user's connections needing a new buffer need to "jump" over those buffers held by the backup process. Once the online PROBKUP routine has completed, as buffers are evicted from the LRU chain or promoted to the MRU chain as appropriate. It is therefore recommended to use Private Buffers with an online PROBKUP to avoid the performance cost immediately after an online backup has completed.
The suggested value for -Bp is 10 Private Buffers to be available for an online backup:
$ PROBKUP online <dbname> <backup_path\backupvolume_name> -Bp 10
- The Private Buffer Pool (-Bp) is an isolated portion of public buffer pool (-B) and therefore does not consume additional shared-memory than currently allocated.
- The total number of Private Buffers is limited to no more than 25% of the Primary Buffer Pool (-B) value.
- If Private Buffers are also used by clients, consider increasing the database startup parameter -Bpmax (64 default).
- Incrementing -Bp value would be a tuning exercise and results are likely to vary due to the inherent differences between environments and the dynamic nature of shared-memory used by production databases. It is unlikely that an online backup will require many more private buffers than the suggested value, provided that the current number of database buffers for -B and -B2 are appropriately scoped for the application environment.
For further information on this subject, refer to the following Article:
