Performance difference between Oracle and Sql server of a factor 2 to 3
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                 Key: OPENJPA-558
                 URL: https://issues.apache.org/jira/browse/OPENJPA-558
             Project: OpenJPA
          Issue Type: Improvement
         Environment: Kodo 4.1.4 (sql server 2005, Oracle 10, Oracle 11, ojdbc6 
oracle driver)
            Reporter: Christiaan
         Attachments: Oracle Performance.zip

I am trying to include support for Oracle in our product. It currently supports 
ms sql server. One of the things I noticed is that many of our unit tests 
perform a factor 2 to 3 slower. I managed to isolate one of the performance 
bottlenecks which is included in the attached testcase. The persistent class is 
basically a 1-to-many relation with itself. The performance bottleneck is for 
the code being executed on getParent(). On my machine it gives the following 
output:

                                ============Executing test for 
Oracle=============
                                There are now 1110 components
                                Getting 1110 parents took 453ms
                                Getting 1110 parents with direct SQL took 156ms
                                ============Executing test for SQL=============
                                There are now 1110 components
                                Getting 1110 parents took 156ms
                                Getting 1110 parents with direct SQL took 156ms

Note, for both sql server and oracle I didn't do any performance tuning. One 
thing to note is that Oracle doesn't generate join syntax (which is probably 
related to issue openjpa-541). I tried setting 
fetchConfig.setJoinSyntax(JoinSyntaxes.SYNTAX_SQL92), but this didn't have any 
effect. However, executing the "and" syntax version versus the join syntax 
version with direct sql gives a time difference of 176 ms vs 156 ms. So this 
doesn't really explain the performance difference. I also tried a different 
oracle driver (datadirect) but this didn't give much difference either. Could 
this performance difference be caused by openjpa code? Did anyone encounter 
this as well?

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