Hibernate select batch-size - performance

Question

Hello,
i have simple J2EE application that shows first 100 Employee records from db (Oracle DB) with Hibernate (version 3). All of the tables have about 10000 records. There are Country(id, name), City(id, name, country_id), Address(id, address, city_id), Company(id, name), Office(id, company_id, address_id), Employee(id, name, address_id), Position(id, name) and Employee_Position_Office(employee_id, position_id, office_id) in db. And i have some problems with batch-size. I need to do it in 4 sql-request (generated by Hibernate). Let's show you what i have:
In my class-mappings i set batch-size=100 and Hibernate creates 3 sql-request for Employee, OfficePosition and Address loading, look:
select * from ( select employee0_.ID as ID6_, employee0_.NAME as NAME6_, employee0_.ADDRESS as ADDRESS6_ from EMPLOYEE employee0_ ) where rownum <= ?
select officeposi0_.EMPLOYEE_ID as EMPLOYEE1_6_1_, officeposi0_.POSITION_ID as POSITION2_1_, officeposi0_.OFFICE_ID as OFFICE3_1_, position1_.ID as ID5_0_, position1_.NAME as NAME5_0_ from EMPLOYEE_POSITION_OFFICE officeposi0_ inner join POSITION position1_ on officeposi0_.POSITION_ID=position1_.ID where officeposi0_.EMPLOYEE_ID in (100x ?)
select address0_.ID as ID2_2_, address0_.ADDRESS as ADDRESS2_2_, address0_.CITY_ID as CITY3_2_2_, city1_.ID as ID1_0_, city1_.NAME as NAME1_0_, city1_.COUNTRY_ID as COUNTRY3_1_0_, country2_.ID as ID0_1_, country2_.NAME as NAME0_1_ from ADDRESS address0_ left outer join CITY city1_ on address0_.CITY_ID=city1_.ID left outer join COUNTRY country2_ on city1_.COUNTRY_ID=country2_.ID where address0_.ID in (100x ?)
And if i change batch-size to number more than 100 nothing changes - this is good.
But then (after these requests) Hibernate generates request(s) for Office loading, and i have some problems with it, let's show you:
My 100 first Employees work in 397 offices (randomly generated) and Hibernate should loads they with 1 request when batch-size is more than 397, when i set batch-size to 397 it works fine (in 1 sql-request),
select office0_.ID as ID4_4_, office0_.COMPANY_ID as COMPANY2_4_4_, office0_.ADDRESS_ID as ADDRESS3_4_4_, (SELECT COUNT(*) FROM EMPLOYEE_POSITION_OFFICE
E WHERE
E.OFFICE_ID=office0_.ID)
as formula0_4_, company1_.ID as ID3_0_, company1_.NAME as NAME3_0_, address2_.ID as ID2_1_, address2_.ADDRESS as ADDRESS2_1_, address2_.CITY_ID as CITY3_2_1_, city3_.ID as ID1_2_, city3_.NAME as NAME1_2_, city3_.COUNTRY_ID as COUNTRY3_1_2_, country4_.ID as ID0_3_, country4_.NAME as NAME0_3_ from OFFICE office0_ left outer join COMPANY company1_ on office0_.COMPANY_ID=company1_.ID left outer join ADDRESS address2_ on office0_.ADDRESS_ID=address2_.ID left outer join CITY city3_ on address2_.CITY_ID=city3_.ID left outer join COUNTRY country4_ on city3_.COUNTRY_ID=country4_.ID where office0_.ID in (397x ?)
but when i set any another number (less or more than 397) Hibernate generates several sql-requests with same "body" but others "tails".
For example, there are results when batch-size = 400.
...in (200x ?)
...in (100x ?)
...in (50x ?)
...in (25x ?)
...in (12x ?)
...in (10x ?)
Tell, please, what i do wrong and can it be fixed. Thx.
My mappings:
<class name="---.Address" table="ADDRESS"
batch-size="100">
<id name="id" type="long">
<column name="ID" />
<generator class="increment" />
</id>
<property name="address" type="java.lang.String">
<column name="ADDRESS" />
</property>
<many-to-one name="city" class="---.City"
fetch="join">
<column name="CITY_ID" />
</many-to-one>
</class>
<class name="---.City" table="CITY">
<id name="id" type="long">
<column name="ID" />
<generator class="increment" />
</id>
<property name="name" type="java.lang.String">
<column name="NAME" />
</property>
<many-to-one name="country" class="---.Country"
fetch="join">
<column name="COUNTRY_ID" />
</many-to-one>
</class>
<class name="---.Company" table="COMPANY">
<id name="id" type="long">
<column name="ID" />
<generator class="increment" />
</id>
<property name="name" type="java.lang.String">
<column name="NAME" />
</property>
</class>
<class name="---.Country" table="COUNTRY">
<id name="id" type="long">
<column name="ID" />
<generator class="increment" />
</id>
<property name="name" type="java.lang.String">
<column name="NAME" />
</property>
</class>
<class name="---.Employee" table="EMPLOYEE"
batch-size="100">
<id name="id" type="long">
<column name="ID" />
<generator class="increment" />
</id>
<property name="name" type="java.lang.String">
<column name="NAME" />
</property>
<many-to-one name="address" class="---.Address"
fetch="join">
<column name="ADDRESS" unique="true" />
</many-to-one>
<map name="officePositions" table="EMPLOYEE_POSITION_OFFICE" lazy="false"
fetch="join" batch-size="100">
<key>
<column name="EMPLOYEE_ID"></column>
</key>
<map-key-many-to-many class="---.Office">
<column name="OFFICE_ID">
</column>
</map-key-many-to-many>
<many-to-many column="POSITION_ID"
class="---.Position" />
</map>
</class>
<class name="---.Office" table="OFFICE"
batch-size="400">
<id name="id" type="long">
<column name="ID" />
<generator class="increment" />
</id>
<many-to-one name="company" class=---.Company"
fetch="join">
<column name="COMPANY_ID" />
</many-to-one>
<many-to-one name="address" class="---.Address"
fetch="join">
<column name="ADDRESS_ID" />
</many-to-one>
<property name="collegues">
<formula>
SELECT COUNT(*) FROM EMPLOYEE_POSITION_OFFICE
E WHERE
E.OFFICE_ID=ID
</formula>
</property>
</class>
<class name="---.Position" table="POSITION">
<id name="id" type="long">
<column name="ID" />
<generator class="increment" />
</id>
<property name="name" type="java.lang.String">
<column name="NAME" />
</property>
</class>
Hibernate cfg:
<hibernate-configuration>
<session-factory>
<property name="connection.url">jdbc:oracle:thin:#localhost:1521:xe</property>
<property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
<property name="connection.username">---</property>
<property name="connection.password">----</property>
<property name="connection.pool_size">10</property>
<property name="current_session_context_class">thread</property>
<property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>
<property name="hibernate.use_sql_comments">false</property>
<property name="hibernate.format_sql">false</property>
<property name="hibernate.show_sql">true</property>
<mapping resource="---/Country.hbm.xml" />
<mapping resource="---/City.hbm.xml" />
<mapping resource="---/Address.hbm.xml" />
<mapping resource="---/Company.hbm.xml" />
<mapping resource="---/Office.hbm.xml" />
<mapping resource="---/Position.hbm.xml" />
<mapping resource="---/Employee.hbm.xml" />
</session-factory>