Release 10.1B: OpenEdge Replication
User Guide
After-image extent sizing on a source database
After you estimate the volume of after-image data your database generates, you can resize the after-image extents for use with OpenEdge Replication. Progress Software Corporation recommends that the size of one after-image extent have enough capacity to store four hours of typical database activity when running OpenEdge Replication. Additionally, Progress Software Corporation further recommends that the total size of all after-image extents have the capacity to store one week of typical database activity. These recommendations are based on the following:
- The total capacity of your source database after-image extents must include additional capacity to allow for some target database downtime.
- Most simple hardware failures can be resolved within a four-hour period. For example, if a drive controller or network card fails, it is a simple operation to have another installed.
- In certain situations, it may be necessary to have your target machine out of service for an extended length of time. The total after-image storage allocated must have the capacity to store large numbers of transaction-log records.
There are additional transaction-log records written by the RDBMS when a database is enabled as a source database. These additional transaction-log records require additional after-image space, referred to as replication overhead. In order to calculate the replication overhead, the estimated after-image size information (obtained in the "Calculating current after-image volume" section) must be multiplied by 1.5.
The following examples demonstrate how to calculate the source database after-image extent sizes and total capacity when using fixed after-image extents. The calculated after-image extent size and total after-image capacity are shown in bold at the bottom of each of the tables.
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