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From Shubbis <>
Subject Re: Slow performance with OpenJPA when selecting from a ManyToMany relation.
Date Tue, 17 Mar 2009 09:56:00 GMT

Hi again,

Thanks for your patience and I am sorry for the late reply, but we are only
stationed at the offices three days a week.

I must admit i don't understand what you mean by test harness. If you could
explain i will gladly post it.

In the meantime I have created a new project and added OpenJPA capabilities
to this one in hopes of discovering what the problem is, but alas I did not.
My new project is of a much simpler setup, it consists of the following

Main class for running simple test:
	public static void main(String[] args) throws Exception {
		EntityManagerFactory factory =
Persistence.createEntityManagerFactory("OpenJPAPU", System.getProperties());
		EntityManager em = factory.createEntityManager();
		OpenJPAEntityManager o = OpenJPAPersistence.cast(em);

		WearhouseDAO wd = new WearhouseDAO();
		long starttid = System.currentTimeMillis();
		for(int i = 1; i <= 500; i++){
			Wearhouse w = wd.findById(o, i);
//			System.out.println(w.getWearhouseName());
		System.out.println(System.currentTimeMillis() - starttid);

Wearhouse Entity class (same as before)
WearhouseDAO class using the following method:
	public Wearhouse findById(OpenJPAEntityManager o, Integer id) {
		try {
			Wearhouse instance = o.find(Wearhouse.class, id);
			return instance;
		} catch (RuntimeException re) {
			throw re;

Storagecategory Entity class (same as before)
StoragecategoryDAO class using the following method:
	public Storagecategory findById(OpenJPAEntityManager o, Integer id) {
		try {
			Storagecategory instance = o.find(Storagecategory.class, id);
			return instance;
		} catch (RuntimeException re) {
			throw re;

The database is still MySQL and this time I've let OpenJPA build the schema.

No difference in the resulting time..

Thanks for reading,


Pinaki Poddar wrote:
> Hi,
>   I ran the Wearhouse-StorageCategory model you have posted (thank you for
> a clean test). Against 500 categories and 200 wearhouses and a cardinality
> of 10 categories per wearhouse. The domain classes were enhanced at
> build-time. The database is MySQL and the tests ran in my pedestrian
> laptop. Here are the results for finding Wearhouses 500 times in a loop.
>    Without connection pool : 2360 ms.
>    With connection pool     :  734ms
> Given these numbers are quite in contrast with your observations, I will
> request you to post the test harness you used to measure the number, so
> that we can investigate further.
> Few comments:
>   1. If performance is higher priority than ordering, consider using Set<>
> instead of List<>
>   2. Consider using a connection pool, if possible [1]
> [1]
>   Regards --
> PS: "Aristotle maintained that women have fewer teeth than men; although
> he was twice married, it never occurred to him to verify this statement by
> examining his wives' mouths." -- 
>     The Impact of Science on Society, 1952 - Bertrand Russell

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