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Posted: Mon Feb 18, 2008 9:20 pm
by JoshGeorge
For Kenneth:
Good post. Again I'm not trying to debate on the best approach to take the seed. Undoubtedly, it is from the database. Approach I posted is on a complete tool based one.
Thanks to you Kenneth! I have included your point and updated the blog post.
This case you need to pick the max value from the target table and use the same strategy specified above. Pass it thru a transformer and update the environment variable before the start of main job using the same conditions.
Posted: Mon Feb 18, 2008 11:17 pm
by chulett
kcbland wrote:For Craig:
If you create a table with a primary key index in Oracle, Sybase, etc, you can't drop the index without dropping the table. If you create the table without a primary key index, but add a unique index afterwards, the database will use that one just the same as a primary key index.
Now why would one want to drop a primary key index? DUPLICATES!! AHAHHHAHHAHA
I got 'em!
If you DIRECT PATH bulk load your table in Oracle, the duplicates aren't found until the load has completed and the deferred index updates are attempted. AAHAHAHHAHAHAH Unusable indexes due to duplicates! Now try to find them!!! AHAHAHHAAH You can't query the table and you can't drop the index.
If you created a secondary unique index, you have to find duplicates without the benefit of an index.
That's why it's recommended that you use non-unique secondary indexes instead of unique or primary key indexes in data warehouses.
So, go to AskTom.Oracle.com and read the wisdom therein, better yet, buy his books. He speaks specifically to the differences between OLTP and OLAP architectures. The gem is the one about non-unique secondary indexes - that one is powerful in Oracle DIRECT path loaded surrogate key managed environments.
Ah... I see that I misread you. I thought you were simply saying that having a surrogate key as the primary key was the bad idea. I'm aware of the indexing issues you've noted, however you've articulated it much mo' better than I probably could have - thanks for that. Heck, I've just been the victim of this
exact issue - bulk load with duplicate primary keys that leaves indexes 'unusable' without any hint of a problem from sqlldr.
By the way, I'm pretty sure you
can query the table as long as you specifically avoid usage of the unusable index. For Oracle, that can mean a FULL hint will allow you to full table scan the table and find the duplicates. Or at least it just worked for the situation I had found myself in.
I've read his site and have at least one of Tom's books around here somewhere. However, I rarely get the chance to leverage some of those gems as (so far) the database has either been already in place or under the creative control of other folks.
Posted: Mon Feb 18, 2008 11:32 pm
by ray.wurlod
For Ken: did you mean to add five exclamation points after each of those maniacal laughs?
(See Maskerade by Terry Pratchett)
Posted: Tue Feb 19, 2008 7:31 am
by kcbland
chulett wrote:
By the way, I'm pretty sure you can query the table as long as you specifically avoid usage of the unusable index. For Oracle, that can mean a FULL hint will allow you to full table scan the table and find the duplicates. Or at least it just worked for the situation I had found myself in.
The DBA's have to get involved, disabling indexes and such, but the problem is the delete. You need to delete the loaded rows and update the index, kind of hard to do if it's disabled. If it's enabled, it's corrupt, and won't allow deletes. To find the duplicates your query has to look at the surrogate keys and group by skey having count(1) > 1 and will use the index so won't work. Can't drop a primary key index, so even disabled it doesn't help you. At least if a secondary index it can be dropped, but a non-unique index will still be usable and allow you to do an efficient query and delete.
Posted: Tue Feb 19, 2008 7:38 am
by kcbland
ray.wurlod wrote:For Ken: did you mean to add five exclamation points after each of those maniacal laughs?
(See Maskerade by Terry Pratchett)
I was in a weird mood yesterday, hence my Opera Ghost laughter.
Posted: Tue Feb 19, 2008 7:45 am
by chulett
Great... The Phantom of the Exchange lives!
