Kbase P103877: Estimating After Image disk space requirements
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
04/05/2005 |
|
Status: Unverified
GOAL:
Estimating After Image disk space requirements
GOAL:
How to estimate disk space required for After Image Extents?
FIX:
Before creating after-image (AI) files, it is important to accurately estimate the amount of disk space required to hold all the AI data for your database. Even when you use variable extents, if the disk runs out of space and there is no empty AI extent available, you must perform emergency maintenance or the database is forced to shut down. See Chapter 8, "Recovering a Database," for details. To prevent the database engine from shutting down when it exhausts AI disk space, start your database with the after-image stall (-aistall) startup parameter.
To determine the amount of AI file space required, use the PROMON utility BI Log Activity Display to monitor the number of BI writes that occur during the activity period that you want to use after-imaging. The information that is written in the BI file closely matches what is written in the AI file. Typically 0.05% fewer bytes are written to an AI file than are written to the BI file. Therefore, the BI Bytes written statistic provides a close estimate of the space required for an AI file for the same activity period.
Measure the BI Bytes written statistic several times toward the end of the activity period that you are considering using after-imaging. If your workload varies from day to day or peaks during end-of-month processing, count the BI writes during a peak period to ensure that you allocate enough space to handle peak days. If the workload grows, make sure you increase the amount of space available for AI files. Always have extra disk space available for unanticipated growth of the AI file.