Serious performance flaws in Manager data retrieval
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Key: TORQUE-52
URL: http://issues.apache.org/jira/browse/TORQUE-52
Project: Torque
Issue Type: Bug
Components: Generator
Affects Versions: 3.1.1, 3.2, 3.2.1
Environment: Any
Reporter: Scott Eade
Where a parent child relationship exists, Torque generates methods such as
getParentsJoinChild(). You use this method because you know you are going to
access the Child objects and you want to eliminate a database hit to retrieve
each one.
Problem 1: If you do not configure caching for the Child object the database
will be hit EVERY time child is retrieved - this includes the check for Parent
objects with common child objects (if a previously retrieved Parent has a Child
in common then subsequently retrieved Parent instances are linked to the
previously retrieved Child instances). The result is that in an attempt to
avoid hitting the database for every child the code actually hammers the
database according to the Fibonacci series. When you eventually retrieve the
Child from the Parent it goes and hits the database anyway (this is the hit you
would have been attempting to avoid by using getParentsJoinChild() in the
first place).
Problem 2: If you _have_ configured caching of Child elements then
getParentsJoinChild() is still a total waste of cycles since the eventual
retrieval of Child objects does not utilise any of the additional work that was
performed - it just goes and grabs the Child from the cache.
Conclusion: The getParentsJoinChild() methods that are generated when Managers
are enabled are not only ineffectual when caching is configured, they are down
right dangerous when it is not.
Solution: The code generated for getChild() when Managers are enabled should be
very similar to the code generated when they are not (i.e. a local copy of the
Child object should be retained by the Parent) - the difference would be that
the generated line that retrieves Child when no local copy exists should use
the Manager's getInstance() method to retrieve the object via the cache rather
than ChildPeer.retrieveByPK().
It is probably not that hard to fix.
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