Running, in Oracle compatible mode, you get a set of system catalog tables that 'resemble' what you see in Oracle. Column names similarity aside, there are plenty of gotchas that you need to be aware of.
eg: You get 'USER_INDEXES' in DB2 if you create the DB in Oracle compatible mode. However, the column values could mean something totally different.
If you see the column CLUSTERING_FACTOR in USER_INDEXES, it is definitely related to index 'clustering' , but the value is no way what you expect from a 'real' Oracle DB. This CLUSTERING_FACTOR is actually the CLUSTERFACTOR in DB2's original 'syscat.indexes'. If you have a table with , say, 100000 pages, you might have a CLUSTERING_FACTOR of just 1, which can be very puzzling to those coming straight from the Oracle world.
To confuse matter, there is another value called 'CLUSTERRATIO' in syscat.indexes, which is also an indicator of the data clustering ...
I will just leave a 'WARNING' sign here ....
No comments:
Post a Comment