This chapter discusses the following topics:
This section covers issues related to Java coding and performance. The guidelines outlined are not specific to Application Server, but are general rules that are useful in many situations. For a complete discussion of Java coding best practices, see the Java Blueprints.
Serialization and deserialization of objects is a CPU-intensive procedure and is likely to slow down your application. Use the transient keyword to reduce the amount of data serialized. Additionally, customized readObject() and writeObject() methods may be beneficial in some cases.
To improve performance, instead of using string concatenation, use StringBuffer.append().
String objects are immutable—they never change after creation. For example, consider the following code:
String str = "testing"; str = str + "abc";
The compiler translates this code as:
String str = "testing"; StringBuffer tmp = new StringBuffer(str); tmp.append("abc"); str = tmp.toString();
Therefore, copying is inherently expensive and overusing it can reduce performance significantly.
Explicitly assigning a null value to variables that are no longer needed helps the garbage collector to identify the parts of memory that can be safely reclaimed. Although Java provides memory management, it does not prevent memory leaks or using excessive amounts of memory.
An application may induce memory leaks by not releasing object references. Doing so prevents the Java garbage collector from reclaiming those objects, and results in increasing amounts of memory being used. Explicitly nullifying references to variables after their use allows the garbage collector to reclaim memory.
One way to detect memory leaks is to employ profiling tools and take memory snapshots after each transaction. A leak-free application in steady state will show a steady active heap memory after garbage collections.
Modern optimizing dynamic compilers can perform inlining and other inter-procedural optimizations, even if Java methods are not declared final. Use the keyword final as it was originally intended: for program architecture reasons and maintainability.
Only if you are absolutely certain that a method must not be overridden, use the final keyword.
The dynamic compiler can perform some constant folding optimizations easily, when you declare constants as static final variables.
Adding finalizers to code makes the garbage collector more expensive and unpredictable. The virtual machine does not guarantee the time at which finalizers are run. Finalizers may not always be executed, before the program exits. Releasing critical resources in finalize() methods may lead to unpredictable application behavior.
Declare method arguments final if they are not modified in the method. In general, declare all variables final if they are not modified after being initialized or set to some value.
Do not synchronize code blocks or methods unless synchronization is required. Keep synchronized blocks or methods as short as possible to avoid scalability bottlenecks. Use the Java Collections Framework for unsynchronized data structures instead of more expensive alternatives such asjava.util.HashTable.
Using a javax.activation.DataHandler for a SOAP attachment will improve performance.
A mapping of certain MIME types to Java types.
Any MIME type is mappable to a javax.activation.DataHandler .
As a result, send an attachment (.gif or XML document) as a SOAP attachment to an RPC style web service by utilizing the Java type mappings. When passing in any of the mandated Java type mappings (appropriate for the attachment’s MIME type) as an argument for the web service, the JAX-RPC runtime handles these as SOAP attachments.
For example, to send out an image/gif attachment, use java.awt.Image, or create a DataHandler wrapper over your image. The advantages of using the wrapper are:
Reduced coding: You can reuse generic attachment code to handle the attachments because the DataHandler determines the content type of the contained data automatically. This feature is especially useful when using a document style service. Since the content is known at runtime, there is no need to make calls to attachment.setContent(stringContent, "image/gif"), for example.
Improved Performance: Informal tests have shown that using DataHandler wrappers doubles throughput for image/gif MIME types, and multiplies throughput by approximately 1.5 for text/xml or java.awt.Image for image/* types.
Many applications running on the Application Server use servlets or JavaServer Pages (JSP) technology in the presentation tier. This section describes how to improve performance of such applications, both through coding practices and through deployment and configuration settings.
This section provides some tips on coding practices that improve servlet and JSP application performance.
Follow these general guidelines to increase performance of the presentation tier:
Minimize Java synchronization in servlets.
Don’t use the single thread model for servlets.
Use the servlet’s init() method to perform expensive one-time initialization.
Avoid using System.out.println() calls.
In the servlet multithread model (the default), a single instance of a servlet is created for each application server instance. All requests for a servlet on that application instance share the same servlet instance. This can lead to thread contention if there are synchronization blocks in the servlet code. So, avoid using shared modified class variables, since they create the need for synchronization.
Follow these guidelines when using HTTP sessions:
Create sessions sparingly. Session creation is not free. If a session is not required, do not create one.
Use javax.servlet.http.HttpSession.invalidate() to release sessions when they are no longer needed.
Keep session size small, to reduce response times. If possible, keep session size below seven KB.
Use the directive <%page session="false"%> in JSP files to prevent the Application Server from automatically creating sessions when they are not necessary.
Don’t cache transaction data in HttpSession. Access to data in an HttpSession is not transactional. Do not use it as a cache of transactional data, which is better kept in the database and accessed using entity beans. Transactions will rollback upon failures to their original state. However, stale and inaccurate data may remain in HttpSession objects. The Application Server provides “read-only” bean-managed persistence entity beans for cached access to read-only data.
Follow these configuration tips to improve performance. These tips are intended for production environments, not development environments.
To improve class loading time, avoid having excessive directories in the server CLASSPATH. Put application-related classes into JAR files.
HTTP response times are dependent on how the keep-alive subsystem and the HTTP server is tuned in general. For more information, see HTTP Service Settings
Get patch 111308-03 from SunSolve Onlineand install it.
Edit the startserv script located in bin/startserv for your domain, and define the LD_PRELOAD environment variable to be /usr/lib/libmtmalloc.so.
The exact syntax to define an environment variable depends on the shell you use.
Cache servlet results when possible. For more information, see Chapter 5, Developing Web Applications, in Sun Java System Application Server Enterprise Edition 8.2 Developer’s Guide.
If an application does not contain any EJB components, deploy the application as a WAR file, not an EAR file.
The security manager is expensive because calls to required resources must call the doPrivileged() method and must also check the resource with the server.policy file. If you are sure that no malicious code will be run on the server and you do not use authentication within your application, then you can disable the security manager.
To disable use of the server.policy file, use the Admin Console. Under Configurations > config-name > JVM Settings (JVM Options) delete the option that looks like this:
The Application 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:
The goals of EJB performance tuning are:
Increased speed - Cache as many beans in the EJB caches as possible to increase speed (equivalently, decrease response time). Caching eliminates CPU-intensive operations. However, since memory is finite, as the caches become larger, housekeeping for them (including garbage collection) takes longer.
Decreased memory consumption - Beans in the pools or caches consume memory from the Java virtual machine heap. Very large pools and caches degrade performance because they require longer and more frequent garbage collection cycles.
Improved functional properties - Functional properties such as user time-out, commit options, security, and transaction options, are mostly related to the functionality and configuration of the application. Generally, they do not compromise functionality for performance. In some cases, you might be forced to make a “trade-off” decision between functionality and performance. This section offers suggestions in such cases.
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.
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.
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.
where moduleName is x_jar for module x.jar.
.stateless-session-bean.beanName .bean-pool .bean-method.methodName
.stateful-session-bean.beanName .bean-cache .bean-method.methodName
.entity-bean.beanName .bean-cache .bean-pool .bean-method.methodName
.message-driven-bean.beanName .bean-pool .bean-method.methodName (methodName = onMessage)
For standalone beans, use this pattern:
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 16, Monitoring Components and Services, in Sun Java System Application Server Enterprise Edition 8.2 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:
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 as much as possible to improve the overall performance of your application. For more information, see Tuning Tips for Specific Types of EJB Components
Stateless Session Beans and Message Driven Beans
Stateful Session Beans
Container Managed Persistence (CMP) entity beans configured as read-only
Bean Managed Persistence (BMP) entity beans configured as read-only
Caching can greatly improve performance when used wisely. For example:
Cache EJB references: To avoid a JNDI lookup for every request, cache EJB references in servlets.
Cache home interfaces: Since repeated lookups to a home interface can be expensive, cache references to EJBHomes in the init() methods of servlets.
Cache EJB resources: Use setSessionContext() or ejbCreate() to cache bean resources. This is again an example of using bean lifecycle methods to perform application actions only once where possible. Remember to release acquired resources in the ejbRemove() method.
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 Java System Application Server Enterprise Edition 8.2 Troubleshooting Guidefor more details.
Removing unneeded stateful session beans avoids passivating them, which requires disk operations.
Follow these tips when using the EJB cache and pools to improve performance:
Explicitly call remove(): Allow stateful session EJB components to be removed from the container cache by explicitly calling of the remove() method in the client.
Tune the entity EJB component’s pool size: Entity Beans use both the EJB pool and cache settings. Tune the entity EJB component’s pool size to minimize the creation and destruction of beans. Populating the pool with a non-zero steady size before hand is useful for getting better response for initial requests.
Cache bean-specific resources: Use the setEntityContext() method to cache bean specific resources and release them using the unSetEntityContext() method.
Load related data efficiently for container-managed relationships (CMRs). For more information, see Pre-fetching Container Managed Relationship (CMR) Beans
Identify read-only beans: Configure read-only entity beans for read only operations. For more information, see Read-Only Entity Beans
This section describes some considerations when EJB components are used by local and remote clients.
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.
By default, the Application 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:
The application predates the EJB 2.0 specification and was written without any local interfaces.
There are bean-to-bean calls and the client beans are written without making any co-location assumptions about the called beans.
For these cases, the Application 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 Java System Application Server Enterprise Edition 8.2 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:
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.
This section provides some tips to improve performance when using transactions.
Container-managed transactions are preferred for consistency, and provide better performance.
To avoid resources being held unnecessarily for long periods, a transaction should not encompass user input or user think time.
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.
For very large transaction chains, use the transaction attribute TX_REQUIRED. To ensure EJB methods in a call chain, use the same transaction.
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.
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.
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.
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:
This section discusses two special performance-enhancing techniques: version consistency and request partitioning.
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:
The first time the bean is used, the ejbLoad() method loads the bean as normal, including loading the version number from the database.
The ejbStore() method checks the version number in the database versus its value when the EJB component was loaded.
If the version number has been modified, it means that there has been simultaneous access to the EJB component and ejbStore() throws a ConcurrentModificationException.
Otherwise, ejbStore() stores the data and completes as normal.
The ejbStore() method performs this validation at the end of the transaction regardless of whether any data in the bean was modified.
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 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).
Configure additional threadpools for EJB execution using the Admin Console.
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">
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>
Restart the Application Server.
This section provides tips for tuning various specific types of EJB components:
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.
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.
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 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 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:
Database rows represented by the bean do not change.
The application can tolerate using out-of-date values for the bean.
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:
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).
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>
Here are some tips to improve the performance of database access.
When dealing with large amounts of data, such as searching a large database, use JDBC directly rather than using Entity EJB components.
Combine business logic with the Entity EJB component that holds the data needed for that logic to process.
To ensure that connections are returned to the pool, always close the connections after use.
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 .
JMS connections are served from a connection pool. This means that calling getConnection() on a Queue connection factory is fast.
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 J2EE 1.4 applications; the Sun Java System Application Server enforces that restriction where previous (J2EE 1.3-based) application servers did not.
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
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.