The answer should leap out right out of the query plan
Perhaps there's join factorization going on. See
https://blogs.oracle.com/optimizer/entry/optimizer_transformations_join_factorization
But the best bet is to examine the query plan.
Iggy
Date: Wed, 21 Oct 2015 11:47:18 -0400
Subject: performance. 7 queries independent queries takes 3s with union all in
view 98s
From: jcdrpllist@xxxxxxxxx
To: oracle-l@xxxxxxxxxxxxx
Hello if you can help please
I found something very interesting, I tested two times to be sure. 11.2.0.3
There is a view having 7 queries joined with union all
query1
union all
query2
union all
...
When executed in the view all 7 takes 98s
If in the same view I put only one query at a time I get 3s total, the query is
unchanged
The problem is using a hash join instead of nested loops
1 1.38s
2 0.04s
3 1.11s
4 0.05s
5 0.35s
6 0.02s
7 0.09s
all 7 98x
Thank you :)
