Re: extraneous joins OPENJPA-134

[catalina shaw]

Regardless the ManyToOne is EAGER by default, when its
inverse relationship if
1. set to EAGER  (select a from a a;  a has the OneToManyRelation property)
or
2. set to LAZY but Eagerly Fetched by query (select ... from a a join fetch
a.OneToManyRelation )

We see unneeded joins being generated.

The issue is why generating the extraneous joins that can be optimized away.



I've looked at the code and it looks correct to me and tried various



things like making the inverse LAZY. But it always generating the



extraneous join. I've attached the entity source code.







The relationship causing problem is







@ManyToOne



@JoinColumn(name=ACCOUNT_ACCOUNTID)



private Accountejb2 account2;

ManyToOne is eager by default, so right now both sides are eager.

RE: extraneous joins OPENJPA-134

[Patrick Linskey]

What if just one side is eager? Also, is the @OneToMany's mappedBy
attribute set up correctly?

-Patrick

-- 
Patrick Linskey
BEA Systems, Inc. 

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 -Original Message-
 From: David Wisneski [mailto:[EMAIL PROTECTED] 
 Sent: Wednesday, February 14, 2007 3:27 PM
 To: open-jpa-dev
 Subject: extraneous joins OPENJPA-134
 
 Hi Patrick or Abe,
 
 I was wondering if any of you have noticed the following problem.  (
 this is written up as OPENJPA-134).  This shows up as a performance
 problem in applications when we compare with  Hibernate.
 
 If I have a M:1 relationship and I make both sides of the relationship
 EAGER in the mapping, OR  I do a  join fetch of the multi side
 relationship,  we see an extra join in the generated sql.
 
 Example:  I have a Dept - Emp with inverse Emp-Dept.
  If both sides are EAGER in mapping I get the sql
 
   select ..  from dept t0 join emp t1 on(...) join dept t2 on (...)
 
  If both sides are LAZY and I do EJB query
   select  d from Dept d left join fetch d.emps
 
 the generated sql is
   select ...  from dept t0 left join emp t1 on(...) join dept 
 t2 on(...)
 
 The extra  join dept t2 on(...) seems to be extraneous and has a
 serious impact on performance.   Since I already joined Dept with Emp,
 there is no need to join it back to the Dept because the Dept-Emp and
 Emp-Dept relationships are inverses of the same foreign key.
 
 Have you noticed this same problem?  Might you have a quick fix that
 you can?  Otherwise we will start analyzing to see what might be
 causing it.