Release 10.1B: Progress Fathom 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 Fathom Replication. Progress Software recommends that the size of one after-image extent have enough capacity to store four hours of typical database activity when running Fathom Replication. Additionally, Progress 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:

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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