ROWDEPENDENCIES Overhead in Oracle

Question

I'm experimenting with a change capture architecture for ETL processing that is based on ora_rowscn, and have rebuilt the source tables with ROWDEPENDENCIES to isolate the SCN's to only those rows modified (as opposed to block-level tagging). I'm aware of the extra 6 bytes/row of space overhead, but it is not obvious to me what other impact this would have.

My question: What would be the extra work the RDBMS engine would do with rowdependencies enabled for commits and rollbacks? For my source tables with 100 to 500 rows/block I realize I must be writing 100-500x the number of SCN's (for our typical commits), but are there other side effects I'm missing?

Answer 1

Oracle introduced ROWDEPENDENCIES as part of a set of changes to optimize replication. It seems unlikely that they would have gone ahead if it did impact on performance. Certainly I haven't read of anything.

The inestimable Tom Kyte discusses using ROWDEPENDENCIES in one of his books, without any warnings or caveats (beyond mentioning the six bytes). If there are other gotachas I'm sure he would have said so.