I am using Hibernate with Spring. There has been some memory related issues. I tracked it down with a profiler that showed that even after garbage collection, the OR library classes (CGLIB) loaded by Hibernate are still held in memory. As the usage increases, the number of instances that can't be reclaimed is also increasing drastically. In just 20-40 clicks, the system runs out of memory. Btw, the actual persistable/detached objects are cleaned up fine during GC.

I am not sure where to start to debug this. Please help me narrow down the choices I have to get to the bottom of the issue. Thanks a lot!

I am showing one OR class ProductCategory.hbm.xml here.

======================
Hibernate Version: 3.1
======================


<hibernate-mapping>
<class name="com.ti.eps.dealer.product.orm.ProductCategory" table="PRODUCT_CATEGORY" schema="DEALER">
<id name="productCategoryId" type="big_decimal">
<column name="PRODUCT_CATEGORY_ID" precision="22" scale="0" />
<generator class="assigned" />
</id>
<many-to-one name="pageSetup" class="com.ti.eps.dealer.pagesetup.orm.PageSetup" fetch="select" lazy="false">
<column name="PAGE_SETUP_ID" precision="22" scale="0" />
</many-to-one>
<property name="productCategoryName" type="string">
<column name="PRODUCT_CATEGORY_NAME" length="512" not-null="true" />
</property>
<property name="instructSortOrder" type="big_decimal">
<column name="INSTRUCT_SORT_ORDER" precision="22" scale="0" />
</property>
<property name="retailerSortOrder" type="big_decimal">
<column name="RETAILER_SORT_ORDER" precision="22" scale="0" />
</property>
<property name="thumbnailImagePath" type="string">
<column name="THUMBNAIL_IMAGE_PATH" length="512" not-null="true" />
</property>
<property name="productComparisonPath" type="string">
<column name="PRODUCT_COMPARISON_PATH" length="512" />
</property>
<property name="courseGuidePath" type="string">
<column name="COURSE_GUIDE_PATH" length="512" />
</property>
<set name="products" inverse="true" lazy="true">
<key>
<column name="PRODUCT_CATEGORY_ID" precision="22" scale="0" />
</key>
<one-to-many class="com.ti.eps.dealer.product.orm.Product"/>
</set>
</class>
<query name="ProductCategory.getAllCategories">
<![CDATA[from ProductCategory where pageSetup.langId = ? and pageSetup.pageSetupCountries.countryId = ? ]]>
</query>

</hibernate-mapping>

======================
I am using Springs DAOSupport methods to access the OR layer.

Object[] queryValues = {'EN', 'US'};

List list = getHibernateTemplate().findByNamedQuery("ProductCategory.getAllCategories"
queryValues);

======================

Here is what the profiler complained about:

com.ti.eps.dealer.product.orm ProductCategory$$EnhancerByCGLIB$$63a97b50$$FastClassByCGLIB$$fca2633a
com.ti.eps.dealer.product.orm ProductCategory$$FastClassByCGLIB$$b9a9f207

======================

Spring version: 2.0 RC3
======================

Are your sessions long-lived ? Maybe you don't flush/clear often enough ?
Do you respect the short-lived session best practice ?

I am not controlling the sesssions. The following method that I am using to access OR layer is facilitated by Spring. From what I read about
Springs DAO support, it closes sessions after every transaction.

===============
List list = getHibernateTemplate().findByNamedQuery("ProductCategory.getAllCategories"
queryValues);
===============

It lookslike that the Object retained in the memory has been loaded by CGLIB.

You should check your configuration about this. Verify that Spring gives you a new session each time (displaying its address, e.g.) and verify it begins a transaction and commit it each time. I had had some problems with this, mainly due to my poor spring knowlegde.

From your user point of view, what is a transaction ? Is this a dao method call, or do you have an upper layer which can call more than one dao method so to coordinate everything ?

I suppose you're using such class as TransactionProxyFactoryBean to demarcate your tx automatically ?

For me, a transaction is a DAO method call. I am using automatic TX demarcation.

Sure, I will do some more debug of the session/tx demarcation information from Spring. Thank you for the insight!

Looks like you create session factory per request, session factory must be a singleton.

Thank you all for your insights!

Upon one day of profiling this is what I found

1. Hibernate is leaving lot of proxy and CGLIB enhancer instances for each persistable objects open. GC is not able to reclaim them. I guess that is okay for our application as the hibernate OR mapping is complex and there are just too many associations. I think I have less control over here.

2. Also, there are many persistable objects that are instantiated just too many times. I am working on enabling second level caching as most of the data are read-only.

3. I now realize that spring+hibernate has significant overhead in terms of memory consumption.

Finally, a question. I don't understand this TransactionProxyFactoryBean. Why do I need it anyway? I currently don't specify it and the app seems to be working just fine. Our app only reads from the db, never writes.

Yes, I have singleton session factory.

Hi to all, baliukas, if you read it... We all have singleton pattern applied to SessionFactory, but I'd like to have more than one Session object and persistent objects per each Session is it possible?

Thanks in advance