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Sun GlassFish Enterprise Server v2.1.1 Performance Tuning Guide

EJB Performance Tuning

The Enterprise Server’s high-performance EJB container has numerous parameters that affect performance. Individual EJB components also have parameters that affect performance. The value of individual EJB component’s parameter overrides the value of the same parameter for the EJB container. The default values are designed for a single-processor computer system—change them to optimize for other system configurations.

This section covers the following topics:

Goals

The goals of EJB performance tuning are:

Monitoring EJB Components

When the EJB container has monitoring enabled, you can examine statistics for individual beans based on the bean pool and cache settings.

For example, the monitoring command below gives the Bean Cache statistics for a stateful session bean.

asadmin get --user admin --host e4800-241-a --port 4848 
-m specjcmp.application.SPECjAppServer.ejb-module.
   supplier_jar.stateful-session-bean.BuyerSes.bean-cache.*

The following is a sample of the monitoring output:

resize-quantity = -1
 cache-misses = 0
 idle-timeout-in-seconds = 0
 num-passivations = 0
 cache-hits = 59
 num-passivation-errors = 0
 total-beans-in-cache = 59
 num-expired-sessions-removed = 0
 max-beans-in-cache = 4096
 num-passivation-success = 0

The monitoring command below gives the bean pool statistics for an entity bean:

asadmin get --user admin --host e4800-241-a --port 4848 
-m specjcmp.application.SPECjAppServer.ejb-module.
   supplier_jar.stateful-entity-bean.ItemEnt.bean-pool.* 
idle-timeout-in-seconds = 0 
steady-pool-size = 0 
total-beans-destroyed = 0 
num-threads-waiting = 0 
num-beans-in-pool = 54 
max-pool-size = 2147483647 
pool-resize-quantity = 0 
total-beans-created = 255

The monitoring command below gives the bean pool statistics for a stateless bean.

asadmin get --user admin --host e4800-241-a --port 4848 
-m test.application.testEjbMon.ejb-module.slsb.stateless-session-bean.slsb.bean-pool.*
idle-timeout-in-seconds = 200
steady-pool-size = 32
total-beans-destroyed = 12
num-threads-waiting = 0
num-beans-in-pool = 4
max-pool-size = 1024
pool-resize-quantity = 12
total-beans-created = 42

Tuning the bean involves charting the behavior of the cache and pool for the bean in question over a period of time.

If too many passivations are happening and the JVM heap remains fairly small, then the max-cache-size or the cache-idle-timeout-in-seconds can be increased. If garbage collection is happening too frequently, and the pool size is growing, but the cache hit rate is small, then the pool-idle-timeout-in-seconds can be reduced to destroy the instances.

Note –

Specifying a max-pool-size of zero (0) means that the pool is unbounded. The pooled beans remain in memory unless they are removed by specifying a small interval for pool-idle-timeout-in-seconds. For production systems, specifying the pool as unbounded is NOT recommended.

Monitoring Individual EJB Components

To gather method invocation statistics for all methods in a bean, use this command:

asadmin get -m monitorableObject.*

where monitorableObject is a fully-qualified identifier from the hierarchy of objects that can be monitored, shown below.

serverInstance.application.applicationName.ejb-module.moduleName

where moduleName is x_jar for module x.jar.

For standalone beans, use this pattern:

serverInstance.application.applicationName.standalone-ejb-module.moduleName

The possible identifiers are the same as for ejb-module.

For example, to get statistics for a method in an entity bean, use this command:

asadmin get -m serverInstance.application.appName.ejb-module.moduleName
.entity-bean.beanName.bean-method.methodName.*

To find the possible objects (applications, modules, beans, and methods) and object attributes that can be monitored, use the Admin Console. For more information, see Chapter 18, Monitoring Components and Services, in Sun GlassFish Enterprise Server v2.1.1 Administration Guide. Alternatively, use the asadmin list command. For more information, see list(1).

For statistics on stateful session bean passivations, use this command:

asadmin get -m serverInstance.application.appName.ejb-module.moduleName
.stateful-session-bean.beanName.bean-cache.*

From the attribute values that are returned, use this command:

num-passivationsnum-passivation-errorsnum-passivation-success

General Guidelines

The following guidelines can improve performance of EJB components. Keep in mind that decomposing an application into many EJB components creates overhead and can degrade performance. EJB components are not simply Java objects. They are components with semantics for remote call interfaces, security, and transactions, as well as properties and methods.

Use High Performance Beans

Use high-performance beans as much as possible to improve the overall performance of your application. For more information, see Tuning Tips for Specific Types of EJB Components

The types of EJB components are listed below, from the highest performance to the lowest:

  1. Stateless Session Beans and Message Driven Beans

  2. Stateful Session Beans

  3. Container Managed Persistence (CMP) entity beans configured as read-only

  4. Bean Managed Persistence (BMP) entity beans configured as read-only

  5. CMP beans

  6. BMP beans

Use Caching

Caching can greatly improve performance when used wisely. For example:

Use the Appropriate Stubs

The stub classes needed by EJB applications are generated dynamically at runtime when an EJB client needs them. This means that it is not necessary to generate the stubs or retrieve the client JAR file when deploying an application with remote EJB components. When deploying an application, it is no longer necessary to specify the --retrieve option, which can speed up deployment.

If you have a legacy rich-client application that directly uses the CosNaming service (not a recommended configuration), then you must generate the stubs for your application explicitly using RMIC. For more information, see Sun GlassFish Enterprise Server 2.1 Troubleshooting Guidefor more details.

Remove Unneeded Stateful Session Beans

Removing unneeded stateful session beans avoids passivating them, which requires disk operations.

Cache and Pool Tuning Tips

Follow these tips when using the EJB cache and pools to improve performance:

Using Local and Remote Interfaces

This section describes some considerations when EJB components are used by local and remote clients.

Prefer Local Interfaces

An EJB component can have remote and local interfaces. Clients not located in the same application server instance as the bean (remote clients) use the remote interface to access the bean. Calls to the remote interface require marshalling arguments, transportation of the marshalled data over the network, un-marshaling the arguments, and dispatch at the receiving end. Thus, using the remote interface entails significant overhead.

If an EJB component has a local interface, then local clients in the same application server instance can use it instead of the remote interface. Using the local interface is more efficient, since it does not require argument marshalling, transportation, and un-marshalling.

If a bean is to be used only by local clients then it makes sense to provide only the local interface. If, on the other hand, the bean is to be location-independent, then you should provide both the remote and local interfaces so that remote clients use the remote interface and local clients can use the local interface for efficiency.

Using Pass-By-Reference Semantics

By default, the Enterprise Server uses pass-by-value semantics for calling the remote interface of a bean, even if it is co-located. This can be expensive, since clients using pass-by-value semantics must copy arguments before passing them to the EJB component.

However, local clients can use pass-by-reference semantics and thus the local and remote interfaces can share the passed objects. But this means that the argument objects must be implemented properly, so that they are shareable. In general, it is more efficient to use pass-by-reference semantics when possible.

Using the remote and local interfaces appropriately means that clients can access EJB components efficiently. That is, local clients use the local interface with pass-by-reference semantics, while remote clients use the remote interface with pass-by-value semantics.

However, in some instances it might not be possible to use the local interface, for example when:

For these cases, the Enterprise Server provides a pass-by-reference option that clients can use to pass arguments by reference to the remote interface of a co-located EJB component.

You can specify the pass-by-reference option for an entire application or a single EJB component. When specified at the application level, all beans in the application use pass-by-reference semantics when passing arguments to their remote interfaces. When specified at the bean level, all calls to the remote interface of the bean use pass-by-reference semantics. See Value Added Features in Sun GlassFish Enterprise Server v2.1.1 Developer’s Guide for more details about the pass-by-reference flag.

To specify that an EJB component will use pass by reference semantics, use the following tag in the sun-ejb-jar.xml deployment descriptor:

<pass-by-reference>true</pass-by-reference>.

This avoids copying arguments when the EJB component’s methods are invoked and avoids copying results when methods return. However, problems will arise if the data is modified by another source during the invocation.

Improving Performance of EJB Transactions

This section provides some tips to improve performance when using transactions.

Use Container-Managed Transactions

Container-managed transactions are preferred for consistency, and provide better performance.

Don’t Encompass User Input Time

To avoid resources being held unnecessarily for long periods, a transaction should not encompass user input or user think time.

Identify Non-Transactional Methods

Declare non-transactional methods of session EJB components with NotSupported or Never transaction attributes. These attributes can be found in the ejb-jar.xml deployment descriptor file. Transactions should span the minimum time possible since they lock database rows.

Use TX_REQUIRED for Long Transaction Chains

For very large transaction chains, use the transaction attribute TX_REQUIRED. To ensure EJB methods in a call chain, use the same transaction.

Use Lowest Cost Database Locking

Use the lowest cost locking available from the database that is consistent with any transaction. Commit the data after the transaction completes rather than after each method call.

Use XA-Capable Data Sources Only When Needed

When multiple database resources, connector resources or JMS resources are involved in one transaction, a distributed or global transaction needs to be performed. This requires XA capable resource managers and data sources. Use XA capable data sources, only when two or more data source are going to be involved in a transaction. If a database participates in some distributed transactions, but mostly in local or single database transactions, it is advisable to register two separate JDBC resources and use the appropriate resource in the application.

Configure JDBC Resources as One-Phase Commit Resources

To improve performance of transactions involving multiple resources, the Application Server uses last agent optimization (LAO), which allows the configuration of one of the resources in a distributed transaction as a one-phase commit (1PC) resource. Since the overhead of multiple-resource transactions is much higher for a JDBC resource than a message queue, LAO substantially improves performance of distributed transactions involving one JDBC resource and one or more message queues. To take advantage of LAO, configure a JDBC resource as a 1PC resource. Nothing special needs to be done to configure JMS resources.

In global transactions involving multiple JDBC resources, LAO will still improve performance, however, not as much as for one JDBC resource. In this situation, one of the JDBC resources should be configured as 1PC, and all others should be configured as XA.

Use the Least Expensive Transaction Attribute

Set the following transaction attributes in the EJB deployment descriptor file (ejb-jar.xml). Options are listed from best performance to worst. To improve performance, choose the least expensive attribute that will provide the functionality your application needs:

  1. NEVER

  2. TX_NOTSUPPORTED

  3. TX_MANDATORY

  4. TX_SUPPORTS

  5. TX_REQUIRED

  6. TX_REQUIRESNEW

Using Special Techniques

Special performance-enhancing techniques are discussed in the following sections:

Version Consistency

Note –

The technique in section applies only to the EJB 2.1 architecture. In the EJB 3.0 architecture, use the Java Persistence API (JPA).

Use version consistency to improve performance while protecting the integrity of data in the database. Since the application server can use multiple copies of an EJB component simultaneously, an EJB component’s state can potentially become corrupted through simultaneous access.

The standard way of preventing corruption is to lock the database row associated with a particular bean. This prevents the bean from being accessed by two simultaneous transactions and thus protects data. However, it also decreases performance, since it effectively serializes all EJB access.

Version consistency is another approach to protecting EJB data integrity. To use version consistency, you specify a column in the database to use as a version number. The EJB lifecycle then proceeds like this:

Subsequent uses of the bean behave similarly, except that the ejbLoad() method loads its initial data (including the version number) from an internal cache. This saves a trip to the database. When the ejbStore() method is called, the version number is checked to ensure that the correct data was used in the transaction.

Version consistency is advantageous when you have EJB components that are rarely modified, because it allows two transactions to use the same EJB component at the same time. Because neither transaction modifies the data, the version number is unchanged at the end of both transactions, and both succeed. But now the transactions can run in parallel. If two transactions occasionally modify the same EJB component, one will succeed and one will fail and can be retried using the new values—which can still be faster than serializing all access to the EJB component if the retries are infrequent enough (though now your application logic has to be prepared to perform the retry operation).

To use version consistency, the database schema for a particular table must include a column where the version can be stored. You then specify that table in the sun-cmp-mapping.xml deployment descriptor for a particular bean:

<entity-mapping>
    <cmp-field-mapping>
        ...
    </cmp-field-mapping>
    <consistency>
        <check-version-of-accessed-instances>
            <column-name>OrderTable.VC_VERSION_NUMBER</column-name>
        </check-version-of-accessed-instances>
    </consistency>
</entity-mapping>

In addition, you must establish a trigger on the database to automatically update the version column when data in the specified table is modified. The Application Server requires such a trigger to use version consistency. Having such a trigger also ensures that external applications that modify the EJB data will not conflict with EJB transactions in progress.

For example, the following DDL illustrates how to create a trigger for the Order table:

CREATE TRIGGER OrderTrigger
  BEFORE UPDATE ON OrderTable
  FOR EACH ROW
  WHEN (new.VC_VERSION_NUMBER = old.VC_VERSION_NUMBER)
  DECLARE
  BEGIN
    :NEW.VC_VERSION_NUMBER := :OLD.VC_VERSION_NUMBER + 1;
  END;

Request Partitioning

Request partitioning enables you to assign a request priority to an EJB component. This gives you the flexibility to make certain EJB components execute with higher priorities than others.

An EJB component which has a request priority assigned to it will have its requests (services) executed within an assigned threadpool. By assigning a threadpool to its execution, the EJB component can execute independently of other pending requests. In short, request partitioning enables you to meet service-level agreements that have differing levels of priority assigned to different services.

Request partitioning applies only to remote EJB components (those that implement a remote interface). Local EJB components are executed in their calling thread (for example, when a servlet calls a local bean, the local bean invocation occurs on the servlet’s thread).

ProcedureTo enable request partitioning

  1. Configure additional threadpools for EJB execution using the Admin Console.

  2. Add the additional threadpool IDs to the Application Server’s ORB.

    You can do this by editing the domain.xml file or through the Admin Console.

    For example, enable threadpools named priority-1 and priority-2 to the <orb> element as follows:


    <orb max-connections="1024" message-fragment-size="1024"
    use-thread-pool-ids="thread-pool-1,priority-1,priority-2">

  3. Include the threadpool ID in the use-thread-pool-id element of the EJB component’s sun-ejb-jar.xml deployment descriptor.

    For example, the following sun-ejb-jar.xml deployment descriptor for an EJB component named “TheGreeter” is assigned to a thread pool named priority-2:

    <sun-ejb-jar> 
  <enterprise-beans> 
    <unique-id>1</unique-id> 
    <ejb> 
      <ejb-name>TheGreeter</ejb-name> 
      <jndi-name>greeter</jndi-name> 
      <use-thread-pool-id>priority-1</use-thread-pool-id> 
    </ejb> 
  </enterprise-beans> 
</sun-ejb-jar>

  4. Restart the Application Server.

Tuning Tips for Specific Types of EJB Components

This section provides tips for tuning various specific types of EJB components:

Entity Beans

Depending on the usage of a particular entity bean, one should tune max-cache-size so that beans that are used less (for example, an order that is created and never used after the transaction is over) are cached less, and beans that are used frequently (for example, an item in the inventory that gets referenced very often), are cached more in numbers.

Stateful Session Beans

When a stateful bean represents a user, a reasonable max-cache-size of beans is the expected number of concurrent users on the application server process. If this value is too low (in relation to the steady load of users), beans would be frequently passivated and activated, causing a negative impact on the response times, due to CPU intensive serialization and deserialization as well as disk I/O.

Another important variable for tuning is cache-idle-timeout-in-seconds where at periodic intervals of cache-idle-timeout-in-seconds, all the beans in the cache that have not been accessed for more than cache-idle-timeout-in-seconds time, are passivated. Similar to an HTTP session time-out, the bean is removed after it has not been accessed for removal-timeout-in-seconds. Passivated beans are stored on disk in serialized form. A large number of passivated beans could not only mean many files on the disk system, but also slower response time as the session state has to be de-serialized before the invocation.

Checkpoint only when needed

In high availability mode, when using stateful session beans, consider checkpointing only those methods that alter the state of the bean significantly. This reduces the number of times the bean state has to be checkpointed into the persistent store.

Stateless Session Beans

Stateless session beans are more readily pooled than entity or the stateful session beans. Valid values for steady-pool-size, pool-resize-quantity and max-pool-size are the best tunables for these type of beans. Set the steady-pool-size to greater than zero if you want to pre-populate the pool. This way, when the container comes up, it creates a pool with steady-pool-size number of beans. By pre-populating the pool it is possible to avoid the object creation time during method invocations.

Setting the steady-pool size to a very large value can cause unwanted memory growth and can result in large garbage collection times. pool-resize-quantity determines the rate of growth as well as the rate of decay of the pool. Setting it to a small value is better as the decay behaves like an exponential decay. Setting a small max-pool-size can cause excessive object destruction (and as a result excessive object creation) as instances are destroyed from the pool if the current pool size exceeds max-pool-size.

Read-Only Entity Beans

Read-only entity beans cache data from the database. Application Server supports read-only beans that use both bean-managed persistence (BMP) and container-managed persistence (CMP). Of the two types, CMP read-only beans provide significantly better performance. In the EJB lifecycle, the EJB container calls the ejbLoad() method of a read-only bean once. The container makes multiple copies of the EJB component from that data, and since the beans do not update the database, the container never calls the ejbStore() method. This greatly reduces database traffic for these beans.

If there is a bean that never updates the database, use a read-only bean in its place to improve performance. A read-only bean is appropriate if either:

For example, an application might use a read-only bean to represent a list of best-seller books. Although the list might change occasionally in the database (say, from another bean entirely), the change need not be reflected immediately in an application.

The ejbLoad() method of a read-only bean is handled differently for CMP and BMP beans. For CMP beans, the EJB container calls ejbLoad() only once to load the data from the database; subsequent uses of the bean just copy that data. For BMP beans, the EJB container calls ejbLoad() the first time a bean is used in a transaction. Subsequent uses of that bean within the transaction use the same values. The container calls ejbLoad() for a BMP bean that doesn’t run within a transaction every time the bean is used. Therefore, read-only BMP beans still make a number of calls to the database.

To create a read-only bean, add the following to the EJB deployment descriptor sun-ejb-jar.xml:

<is-read-only-bean>true</is-read-only-bean>
<refresh-period-in-seconds>600</refresh-period-in-seconds>

Refresh period

An important parameter for tuning read-only beans is the refresh period, represented by the deployment descriptor entity refresh-period-in-seconds. For CMP beans, the first access to a bean loads the bean’s state. The first access after the refresh period reloads the data from the database. All subsequent uses of the bean uses the newly refreshed data (until another refresh period elapses). For BMP beans, an ejbLoad() method within an existing transaction uses the cached data unless the refresh period has expired (in which case, the container calls ejbLoad() again).

This parameter enables the EJB component to periodically refresh its “snapshot” of the database values it represents. If the refresh period is less than or equal to 0, the bean is never refreshed from the database (the default behavior if no refresh period is given).

Pre-fetching Container Managed Relationship (CMR) Beans

If a container-managed relationship (CMR) exists in your application, loading one bean will load all its related beans. The canonical example of CMR is an order-orderline relationship where you have one Order EJB component that has related OrderLine EJB components. In previous releases of the application server, to use all those beans would require multiple database queries: one for the Order bean and one for each of the OrderLine beans in the relationship.

In general, if a bean has n relationships, using all the data of the bean would require n+1 database accesses. Use CMR pre-fetching to retrieve all the data for the bean and all its related beans in one database access.

For example, you have this relationship defined in the ejb-jar.xml file:

<relationships>
    <ejb-relation>
        <description>Order-OrderLine</description>
        <ejb-relation-name>Order-OrderLine</ejb-relation-name>
        <ejb-relationship-role>
            <ejb-relationship-role-name>
                Order-has-N-OrderLines
            </ejb-relationship-role-name>
            <multiplicity>One</multiplicity>
            <relationship-role-source>
                <ejb-name>OrderEJB</ejb-name>
            </relationship-role-source>
            <cmr-field>
                <cmr-field-name>orderLines</cmr-field-name>
                <cmr-field-type>java.util.Collection</cmr-field-type>
            </cmr-field>
        </ejb-relationship-role>
    </ejb-relation>
</relationships>

When a particular Order is loaded, you can load its related OrderLines by adding this to the sun-cmp-mapping.xml file for the application:

<entity-mapping>
    <ejb-name>Order</ejb-name>
    <table-name>...</table-name>
    <cmp-field-mapping>...</cmp-field-mapping>
    <cmr-field-mapping>
        <cmr-field-name>orderLines</cmr-field-name>
        <column-pair>
            <column-name>OrderTable.OrderID</column-name>
            <column-name>OrderLineTable.OrderLine_OrderID</column-name>
        </column-pair>
        <fetched-with>
            <default>
        </fetched-with>
    </cmr-field-mapping>
</entity-mappping>

Now when an Order is retrieved, the CMP engine issues SQL to retrieve all related OrderLines with a SELECT statement that has the following WHERE clause:

OrderTable.OrderID = OrderLineTable.OrderLine_OrderID

This clause indicates an outer join. These OrderLines are pre-fetched.

Pre-fetching generally improves performance because it reduces the number of database accesses. However, if the business logic often uses Orders without referencing their OrderLines, then this can have a performance penalty, that is, the system has spent the effort to pre-fetch the OrderLines that are not actually needed.

Avoid pre-fetching for specific finder methods; this can often avoid that penalty. For example, consider an order bean has two finder methods: a findByPrimaryKey method that uses the orderlines, and a findByCustomerId method that returns only order information and hence doesn’t use the orderlines. If you’ve enabled CMR pre-fetching for the orderlines, both finder methods will pre-fetch the orderlines. However, you can prevent pre-fetching for the findByCustomerId method by including this information in the sun-ejb-jar.xml descriptor:

<ejb>
    <ejb-name>OrderBean</ejb-name>
    ...
    <cmp>
        <prefetch-disabled>
            <query-method>
                <method-name>findByCustomerId</method-name>
            </query-method>
        </prefetch-disabled>
     </cmp>
</ejb>

JDBC and Database Access

Here are some tips to improve the performance of database access.

Use JDBC Directly

When dealing with large amounts of data, such as searching a large database, use JDBC directly rather than using Entity EJB components.

Encapsulate Business Logic in Entity EJB Components

Combine business logic with the Entity EJB component that holds the data needed for that logic to process.

Close Connections

To ensure that connections are returned to the pool, always close the connections after use.

Minimize the Database Transaction Isolation Level

Use the default isolation level provided by the JDBC driver rather than calling setTransactionIsolationLevel(), unless you are certain that your application behaves correctly and performs better at a different isolation level.

Reduce the database transaction isolation level when appropriate. Reduced isolation levels reduce work in the database tier, and could lead to better application performance. However, this must be done after carefully analyzing the database table usage patterns.

Set the database transaction isolation level with the Admin Console on the Resources > JDBC > Connection Pools > PoolName page. For more information on tuning JDBC connection pools, see JDBC Connection Pool Settings .

Tuning Message-Driven Beans

This section provides some tips to improve performance when using JMS with message-driven beans (MDBs).

Use getConnection()

JMS connections are served from a connection pool. This means that calling getConnection() on a Queue connection factory is fast.

Caution – Caution –

Previous to version 8.1, it was possible to reuse a connection with a servlet or EJB component. That is, the servlet could call getConnection() in its init() method and then continually call getSession() for each servlet invocation. If you use JMS within a global transaction, that no longer works: applications can only call getSession() once for each connection. After than, the connection must be closed (which doesn’t actually close the connection; it merely returns it to the pool). This is a general feature of portable Java EE 1.4 applications; the Sun Java System Application Server enforces that restriction where previous (Java EE 1.3-based) application servers did not.

Tune the Message-Driven Bean’s Pool Size

The container for message-driven beans (MDB) is different than the containers for entity and session beans. In the MDB container, sessions and threads are attached to the beans in the MDB pool. This design makes it possible to pool the threads for executing message-driven requests in the container.

Tune the Message-Driven bean’s pool size to optimize the concurrent processing of messages. Set the size of the MDB pool to, based on all the parameters of the server (taking other applications into account). For example, a value greater than 500 is generally too large.

You can configure MDB pool settings in the Admin Console at Configurations > config-name > EJB Container (MDB Settings). You can also set it with asadmin as follows:

asadmin set server.mdb-container.max-pool-size = value

Cache Bean-Specific Resources

Use the setMessageDrivenContext() or ejbCreate() method to cache bean specific resources, and release those resources from the ejbRemove() method.

Limit Use of JMS Connections

When designing an application that uses JMS connections make sure you use a methodology that sparingly uses connections, by either pooling them or using the same connection for multiple sessions.

The JMS connection uses two threads and the sessions use one thread each. Since these threads are not taken from a pool and the resultant objects aren’t pooled, you could run out of memory during periods of heavy usage.

One workaround is to move createTopicConnection into the init of the servlet.

Make sure to specifically close the session, or it will stay open, which ties up resources.