Reduce Redo

Question

Hi Folks
RDBMS: 11gR1
we have a finance controlling database in archivelog mode which performs huge calculations from time to time. the size of the db is 10gb, but when such a report run it generates ~100gb in a couple of hours. our goal is to reduce the redo generation but we cannot adapt the dml (for direct path load etc..). there are 18 tables (including indexes) involved. so we recreated them as global temporary tables. the redo generation decreased of 30% but the reports took 20% longer, which is too long.
my question is, is there a way to reduce the redo generation for this reports?
something like this for the reporting sessions:
alter session set disablelogging=true;
but in a less dangerous way? :)
what we would try next is to create a second database in noarchivelogmode for reporting and get the results via view over database link to the first database.
thanks a lot for any suggestions
regards oviwan

Answer 1

I liked your approach for the first fix but wonder why it took longer - overhead for loading the temp tables? Swapping (probabaly not, since it was only 30% longer)? Missing or unnecessary indexes on the GTTs?
Might be worth a minute or two to think about what is happening before abandonding the GTT approach. If you can figure that out without too much trouble and fix the problem the GTT approach might still be workable
You'll get overhead when transferring the data through the database link; if the second database is on the same box would an offload with an upload using a direct path load be more efficient?
Some loading ideas
* direct path inserts (APPEND if loading heap tables through insert/select)
* If you're going to populate empty tables create indexes after loading the data
* if you're loading through sql use bulk commands (insert/select if possible); avoid context switching from cursor loops