I had left before they were willing to performance test the application. But I heard that after they launched that it was awful.
The Oracle optimizer quits optimizing after the first ~7 joins so we had to do manual optimization after that. Almost every query was at least 7 joins. The guy running the DBA group was following the Data Model Resource Book to a "T", which I think is appropriate for an OLAP database, but is not cool for OLTP.
If you want to see something hilarious, get a 12 join query and add "AND 1=0" on the end of the WHERE clause.
Oracle doesn't look at the query and immediately return no rows, instead the optimizer continues to generate a full plan. Apparently, according to Oracle support, they have no intention of finding "AND false" predicates to shortcut query plan compilation.
Comments
I had left before they were willing to performance test the application. But I heard that after they launched that it was awful.
The Oracle optimizer quits optimizing after the first ~7 joins so we had to do manual optimization after that. Almost every query was at least 7 joins. The guy running the DBA group was following the Data Model Resource Book to a "T", which I think is appropriate for an OLAP database, but is not cool for OLTP.
If you want to see something hilarious, get a 12 join query and add "AND 1=0" on the end of the WHERE clause.
Oracle doesn't look at the query and immediately return no rows, instead the optimizer continues to generate a full plan. Apparently, according to Oracle support, they have no intention of finding "AND false" predicates to shortcut query plan compilation.