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User Guide
OpenEdge Replication and after-imaging : Calculating current database after-image volume : Using before-image VST information

Using before-image VST information

You can also use before-image VSTs to determine approximately how many after-image blocks will be written. The VST table used for this is _ActBILog. The fields with the relevant information are _BiLog-TotWrites and _BiLog-BytesWritn. The _BiLog-TotWrites field's value is an integer representing the number of before-image blocks written to before-image files. Refer to your before-image block size to see how much data is involved. You must also take into account that the before-image block size must be the same as your after-image block size. Take samples at the start of the time period and at the end of the time period; the difference between these samples results in the count of after-image blocks that would have been written.
If you do not have after-imaging enabled for the database, this method is the only choice in calculating after-image volume. Note that you must set up after-imaging for any database you intend to use as an OpenEdge Replication source database.