Object Request Broker tuning guidelines

 

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Use the guidelines in this document any time the Object Request Broker (ORB) is used in a workload.

The ORB is used whenever enterprise beans are accessed through a remote interface. If you experience particularly high or low CPU consumption, you might have a problem with the value of one of the following parameters. Examine these core tuning parameters for every application deployment.

Thread pool adjustments

Size

Tune the size of the ORB thread pool according to your workload. Avoid suspending threads because they have no work ready to process. If threads do not have work ready to process, CPU time is consumed by calling the Object.wait method, performing a context switch. Tune the thread pool size such that the length of time that the threads wait is short enough to prevent them from being destroyed because they are idle too long.

The thread pool size is dependent on your workload and system. In typical configurations, applications need 10 or fewer threads per processor.

However, if your application is performing a very slow backend request, like a request to a database system, a server thread blocks waiting for the backend request to complete. With backend requests, CPU use is fairly low. In this case, increasing the load does not increase CPU use or throughput. Your thread dumps indicate that nearly all the threads are in a call out to the backend resource. In this case, consider increasing the number of threads per processor until throughput improves and thread dumps show that the threads are in other areas of the run time besides the backend call. You should adjust the number of threads only if your backend resource is tuned correctly.

The Allow thread allocation beyond maximum thread size parameter also affects thread pool size, but do not use this parameter unless your back end stops for long periods of time, causing the blocking of all the run-time threads waiting for the backend system instead of processing other work that does not involve the backend system.

You can adjust the thread pool size settings in the console. Click...

Servers | Application servers | server | Container services | ORB service | Thread pool

You can adjust the minimum and maximum number of threads. See Thread pool settings for more information.

Pass by reference

Specify how the ORB passes parameters. If enabled, the ORB passes parameters by reference instead of by value, to avoid making an object copy. If you do not enable the pass by reference option, a copy of the parameter passes rather than the parameter object itself. This can be expensive because the ORB must first make a copy of each parameter object.

You can use this option only when the EJB client and the EJB are on the same classloader. This requirement means that the EJB client and the EJB must be deployed in the same EAR file.

If the EJB client and server are installed in the same WAS instance, and the client and server use remote interfaces, enabling the pass by reference option can improve performance up to 50%. The pass by reference option helps performance only where non-primitive object types are passed as parameters. Therefore, int and floats are always copied, regardless of the call model.

Enable this property with caution because unexpected behavior can occur. If an object reference is modified by the callee, the caller's object is modified as well, since they are the same object.

If you use command-line scripting, the full name of this system property is...

com.ibm.CORBA.iiop.noLocalCopies

Data type	Boolean
Default	Not enabled (false)

The use of this option for enterprise beans with remote interfaces violates EJB Specification, V2.0 (see section 5.4). Object references passed to EJB methods or to EJB home methods are not copied and can be subject to corruption.

Consider the following example:

Iterator iterator = collection.iterator();
MyPrimaryKey pk = new MyPrimaryKey(); while (iterator.hasNext()) {
   pk.id = (String) iterator.next();
   MyEJB myEJB = myEJBHome.findByPrimaryKey(pk);
}

In this example, a reference to the same MyPrimaryKey object passes into WAS with a different ID value each time. Running this code with pass by reference enabled causes a problem within the appserver because multiple enterprise beans are referencing the same MyPrimaryKey object. To avoid this problem, set the com.ibm.websphere.ejbcontainer.allowPrimaryKeyMutation system property to true when the pass by reference option is enabled. Setting the pass by reference option to true causes the EJB container to make a local copy of the PrimaryKey object. As a result, however, a small portion of the performance advantage of setting the pass by reference option is lost.

As a general rule, any application code that passes an object reference as a parameter to an enterprise bean method or to an EJB home method must be scrutinized to determine if passing that object reference results in loss of data integrity or in other problems.

After examining your code, you can enable the pass by reference option by setting the com.ibm.CORBA.iiop.noLocalCopies system property to true. You can also enable the pass by reference option in the console. Click...

Servers | Application servers | server_name | Container services | ORB Service | Pass by reference

Fragment size

The ORB separates messages into fragments to send over the ORB connection. You can configure this fragment size through the com.ibm.CORBA.FragmentSize parameter.

To determine and change the size of the messages that transfer over the ORB and the number of required fragments, perform the following steps:

1. In the console, enable ORB tracing in the ORB Properties page. See Object Request Broker service settings for more information.

2. Enable ORBRas tracing from the logging and tracing page.

3. Increase the trace file sizes because tracing can generate a lot of data.

4. Restart the server and run at least one iteration (preferably several) of the case that you are measuring.

5. Look at the traceable file and do a search for Fragment to follow: Yes.

   This message indicates that the ORB transmitted a fragment, but it still has at least one remaining fragment to send before the entire message arrives. A Fragment to follow: No value indicates that the particular fragment is the last in the entire message. This fragment can also be the first, if the message fit entirely into one fragment.

   If you go to the spot where Fragment to follow: Yes is located, you find a block that looks similar to the following example:

   Fragment to follow:	Yes
   Message size:	4988 (0x137C)
   --
   Request ID:	1411

   This example indicates that the amount of data in the fragment is 4988 bytes and the Request ID is 1411. If you search for all occurrences of Request ID: 1411, you can see the number of fragments that are used to send that particular message. If you add all the associated message sizes, you have the total size of the message that is being sent through the ORB.

6. You can configure the fragment size by setting the com.ibm.CORBA.FragmentSize property. See Object Request Broker custom properties for more information.

Interceptors

Interceptors are ORB extensions that can set up the context before the ORB runs a request. For example, the context might include transactions or activity sessions to import. If the client creates a transaction, and then flows the transaction context to the server, then the server imports the transaction context onto the server request through the interceptors.

Most clients do not start transactions or activity sessions, so most systems can benefit from removing the interceptors that are not required.

To remove the interceptors, manually edit the server.xml file and remove the interceptor lines that are not needed from the ORB section.

Connection Cache Adjustments

Depending on an appserver's workload, and throughput or response-time requirements, you might need to adjust the size of the ORB's connection cache. Each entry in the connection cache is an object that represents a distinct TCP/IP socket endpoint, identified by the hostname or TCP/IP address, and the port number used by the ORB to send a GIOP request or a GIOP reply to the remote target endpoint. The purpose of the connection cache is to minimize the time required to establish a connection by reusing ORB connection objects for subsequent requests or replies. (The same TCP/IP socket is used for the request and corresponding reply.)

For each appserver, the number of entries in the connection cache relates directly to the number of concurrent ORB connections. These connections consist of both the inbound requests made from remote clients and outbound requests made by the appserver. When the server-side ORB receives a connection request, it uses an existing connection from an entry in the cache, or establishes a new connection and adds an entry for that connection to the cache.

The ORB Connection cache maximum and Connection cache minimum properties are used to control the maximum and minimum number of entries in the connection cache at a given time. When the number of entries reaches the value specified for the Connection cache maximum property, and a new connection is needed, the ORB creates the requested connection, adds an entry to the cache and searches for and attempts to remove up to five inactive connection entries from the cache. Because the new connection is added before inactive entries are removed, it is possible for the number of cache entries to temporarily exceed the value specified for the Connection cache maximum property.

An ORB connection is considered inactive if the TCP/IP socket stream is not in use and there are no GIOP replies pending for any requests made on that connection. As the application workload diminishes, the ORB closes the connections and removes the entries for these connections from the cache. The ORB continues to remove entries from the cache until the number of remaining entries is at or below the value specified for the Connection cache maximum property. The number of cache entries is never less then the value specified for the Connection cache minimum property, which must be at least five connections less than the value specified for the Connection cache maximum property.

Adjustments to the connection cache in the client-side ORB are usually not necessary because only a small number of connections are made on that side.

JNI Reader Threads

By default, the ORB uses a Java thread for processing each inbound connection request it receives. As the number of concurrent requests increases, the storage consumed by a large number of reader threads increases and can become a bottleneck in resource-constrained environments. Eventually, the number of Java threads created can cause out-of-memory exceptions if the number of concurrent requests exceeds the system's available resources.

To help address this potential problem, you can configure the ORB to use JNI reader threads where a finite number of reader threads, implemented using native OS threads instead of Java threads, are created during ORB initialization. JNI reader threads rely on the native OS TCP/IP asynchronous mechanism that enables a single native OS thread to handle I/O events from multiple sockets at the same time. The ORB manages the use of the JNI reader threads and assigns one of the available threads to handle the connection request, using a round-robin algorithm. Ordinarily, JNI reader threads should only be configured when using Java threads is too memory-intensive for your application environment.

The number of JNI reader threads you should allocate for an ORB depends on many factors and varies significantly from one environment to another, depending on available system resources and workload requirements. The following potential benefits might be achieved if you use JNI threads:

• Because a fixed number of threads is allocated, memory usage is reduced. This reduction provides significant benefit in environments with unusually large and sustained client-request workloads.

• The time needed to dynamically create and destroy Java threads is eliminated because a fixed number of JNI threads is created and allocated during ORB initialization.

• Each JNI thread can handle up to 1024 socket connections and interacts directly with the asynchronous I/O native OS mechanism, which might provide enhanced performance of network I/O processing.

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Related tasks

Tune the application serving environment

 

Related Reference

Object Request Broker service settings