public static void main(String[] args) {
        // memory close to -Xmx value
        List<EntityManagerFactory> emfs = IntStream.range(0, 50).mapToObj(
                n -> Persistence.createEntityManagerFactory("store",
                        ImmutableMap.of(
                                "javax.persistence.jdbc.driver", "net.sourceforge.jtds.jdbc.Driver",
                                "javax.persistence.jdbc.url", "jdbc:jtds:sqlserver://xxx:1433/xxx",
                                "javax.persistence.jdbc.user", "xxx",
                                "javax.persistence.jdbc.password", "xxx"
                        ))
        ).collect(toList());
        // ~1gib of memory.
        emfs.forEach(EntityManagerFactory::close);   
        try { Thread.sleep(60000); } catch (InterruptedException e) {}
        // *STILL* ~1gib of memory.
}

public static void main(String[] args) {
    // memory close to -Xmx value
    Map<String, String> properties = new HashMap<>();
    List<EntityManagerFactory> emfs = IntStream.range(0, 50).mapToObj(
            n -> Persistence.createEntityManagerFactory("templatePU", properties)
    ).collect(toList());
    // ~1gib of memory.
    emfs.forEach(EntityManagerFactory::close);
    System.gc();
    try { Thread.sleep(60000); } catch (InterruptedException e) {}
    System.gc();
    System.out.println("Done");
}

<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
             http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
             version="2.1">

    <persistence-unit name="templatePU" transaction-type="RESOURCE_LOCAL">

        <description>Hibernate test case template Persistence Unit</description>
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>

        <exclude-unlisted-classes>false</exclude-unlisted-classes>

        <properties>
            <property name="hibernate.archive.autodetection" value="class, hbm"/>

            <property name="hibernate.dialect" value="org.hibernate.dialect.SQLServer2012Dialect"/>
<!--            <property name="hibernate.connection.driver_class" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
            <property name="hibernate.connection.url" value="jdbc:sqlserver://localhost;instance=SQLEXPRESS;databaseName=high_performance_java_persistence"/>-->

            <property name="hibernate.connection.driver_class" value="net.sourceforge.jtds.jdbc.Driver"/>
            <property name="hibernate.connection.url" value="jdbc:jtds:sqlserver://127.0.0.1:1433/high_performance_java_persistence;instance=SQLEXPRESS"/>

            <property name="hibernate.connection.username" value="sa"/>
            <property name="hibernate.connection.password" value="adm1n"/>

            <property name="hibernate.connection.pool_size" value="5"/>

            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="true"/>
            <property name="hibernate.hbm2ddl.auto" value="create-drop"/>

            <property name="hibernate.max_fetch_depth" value="5"/>

            <property name="hibernate.cache.region_prefix" value="hibernate.test"/>
            <property name="hibernate.cache.region.factory_class"
                      value="org.hibernate.testing.cache.CachingRegionFactory"/>

            <!--NOTE: hibernate.jdbc.batch_versioned_data should be set to false when testing with Oracle-->
            <property name="hibernate.jdbc.batch_versioned_data" value="true"/>

            <property name="javax.persistence.validation.mode" value="NONE"/>
            <property name="hibernate.service.allow_crawling" value="false"/>
            <property name="hibernate.session.events.log" value="true"/>
        </properties>

    </persistence-unit>
</persistence>