Chapter 21. The CMP Engine

This chapter will explore the use of container managed persistence (CMP) in JBoss. We will assume a basic familiarity the EJB CMP model and focus on the operation of the JBoss CMP engine. Specifically, we will look at how to configure and optimize CMP applications on JBoss. For more introductory coverage of basic CMP concepts, we recommend Enterprise Java Beans, Fourth Edition (O'Reilly 2004).

21.1. Example Code

This chapter is example-driven. We will work with the crime portal application which stores information about imaginary criminal organizations. The data model we will be working with is shown in Figure 21.1, “The crime portal example classes”.
The crime portal example classes

Figure 21.1. The crime portal example classes

The source code for the crime portal is available in the src/main/org/jboss/cmp2 directory of the example code. To build the example code, run Ant as shown below 
[examples]$ ant -Dchap=cmp2 config
This command builds and deploys the application to the JBoss server. When you start yours JBoss server, or if it is already running, you should see the following deployment messages: 
15:46:36,704 INFO  [OrganizationBean$Proxy] Creating organization Yakuza, Japanese Gangsters
15:46:36,790 INFO  [OrganizationBean$Proxy] Creating organization Mafia, Italian Bad Guys
15:46:36,797 INFO  [OrganizationBean$Proxy] Creating organization Triads, Kung Fu Movie Extras
15:46:36,877 INFO  [GangsterBean$Proxy] Creating Gangster 0 'Bodyguard' Yojimbo
15:46:37,003 INFO  [GangsterBean$Proxy] Creating Gangster 1 'Master' Takeshi
15:46:37,021 INFO  [GangsterBean$Proxy] Creating Gangster 2 'Four finger' Yuriko
15:46:37,040 INFO  [GangsterBean$Proxy] Creating Gangster 3 'Killer' Chow
15:46:37,106 INFO  [GangsterBean$Proxy] Creating Gangster 4 'Lightning' Shogi
15:46:37,118 INFO  [GangsterBean$Proxy] Creating Gangster 5 'Pizza-Face' Valentino
15:46:37,133 INFO  [GangsterBean$Proxy] Creating Gangster 6 'Toohless' Toni
15:46:37,208 INFO  [GangsterBean$Proxy] Creating Gangster 7 'Godfather' Corleone
15:46:37,238 INFO  [JobBean$Proxy] Creating Job 10th Street Jeweler Heist
15:46:37,247 INFO  [JobBean$Proxy] Creating Job The Greate Train Robbery
15:46:37,257 INFO  [JobBean$Proxy] Creating Job Cheap Liquor Snatch and Grab
Since the beans in the examples are configured to have their tables removed on undeployment, anytime you restart the JBoss server you need to rerun the config target to reload the example data and re-deploy the application.

21.1.1. Enabling CMP Debug Logging

In order to get meaningful feedback from the chapter tests, you will want to increase the log level of the CMP subsystem before running running the test. To enable debug logging add the following category to your log4j.xml file: 
<category name="org.jboss.ejb.plugins.cmp">
    <priority value="DEBUG"/>
</category>
In addition to this, it is necessary to decrease the threshold on the CONSOLE appender to allow debug level messages to be logged to the console. The following changes also need to be applied to the log4j.xml file. 
<appender name="CONSOLE" class="org.apache.log4j.ConsoleAppender">
    <errorHandler class="org.jboss.logging.util.OnlyOnceErrorHandler"/>
    <param name="Target"    value="System.out"/>
    <param name="Threshold" value="DEBUG" />

    <layout class="org.apache.log4j.PatternLayout">
        <!-- The default pattern: Date Priority [Category] Message\n -->
        <param name="ConversionPattern" value="%d{ABSOLUTE} %-5p [%c{1}] %m%n"/>
    </layout>
</appender>
To see the full workings of the CMP engine you would need to enable the custom TRACE level priority on the org.jboss.ejb.plugins.cmp category as shown here: 
<category name="org.jboss.ejb.plugins.cmp">
    <priority value="TRACE" class="org.jboss.logging.XLevel"/>
</category>

21.1.2. Running the examples

The first test target illustrates a number of the customization features that will be discussed throughout this chapter. To run these tests execute the following ant target: 
[examples]$ ant -Dchap=cmp2 -Dex=test run-example
22:30:09,862 DEBUG [OrganizationEJB#findByPrimaryKey] Executing SQL: SELECT t0_OrganizationEJ
B.name FROM ORGANIZATION t0_OrganizationEJB WHERE t0_OrganizationEJB.name=?
22:30:09,927 DEBUG [OrganizationEJB] Executing SQL: SELECT desc, the_boss FROM ORGANIZATION W
HERE (name=?)
22:30:09,931 DEBUG [OrganizationEJB] load relation SQL: SELECT id FROM GANGSTER WHERE (organi
zation=?)
22:30:09,947 DEBUG [StatelessSessionContainer] Useless invocation of remove() for stateless s
ession bean
22:30:10,086 DEBUG [GangsterEJB#findBadDudes_ejbql] Executing SQL: SELECT t0_g.id FROM GANGST
ER t0_g WHERE (t0_g.badness > ?)
22:30:10,097 DEBUG [GangsterEJB#findByPrimaryKey] Executing SQL: SELECT t0_GangsterEJB.id FRO
M GANGSTER t0_GangsterEJB WHERE t0_GangsterEJB.id=?
22:30:10,102 DEBUG [GangsterEJB#findByPrimaryKey] Executing SQL: SELECT t0_GangsterEJB.id FRO
M GANGSTER t0_GangsterEJB WHERE t0_GangsterEJB.id=?
These tests exercise various finders, selectors and object to table mapping issues. We will refer to the tests throughout the chapter.
The other main target runs a set of tests to demonstrate the optimized loading configurations presented in Section 21.7, “Optimized Loading”. Now that the logging is setup correctly, the read-ahead tests will display useful information about the queries performed. Note that you do not have to restart the JBoss server for it to recognize the changes to the log4j.xml file, but it may take a minute or so. The following shows the actual execution of the readahead client: 
[examples]$ ant -Dchap=cmp2 -Dex=readahead run-example
When the readahead client is executed, all of the SQL queries executed during the test are displayed in the JBoss server console. The important items of note when analyzing the output are the number of queries executed, the columns selected, and the number of rows loaded. The following shows the read-ahead none portion of the JBoss server console output from readahead: 
22:44:31,570 INFO  [ReadAheadTest] 
########################################################
### read-ahead none
###
22:44:31,582 DEBUG [GangsterEJB#findAll_none] Executing SQL: SELECT t0_g.id FROM GANGSTER t0_
g ORDER BY t0_g.id ASC
22:44:31,604 DEBUG [GangsterEJB] Executing SQL: SELECT name, nick_name, badness, organization
, hangout FROM GANGSTER WHERE (id=?)
22:44:31,615 DEBUG [GangsterEJB] Executing SQL: SELECT name, nick_name, badness, organization
, hangout FROM GANGSTER WHERE (id=?)
22:44:31,622 DEBUG [GangsterEJB] Executing SQL: SELECT name, nick_name, badness, organization
, hangout FROM GANGSTER WHERE (id=?)
22:44:31,628 DEBUG [GangsterEJB] Executing SQL: SELECT name, nick_name, badness, organization
, hangout FROM GANGSTER WHERE (id=?)
22:44:31,635 DEBUG [GangsterEJB] Executing SQL: SELECT name, nick_name, badness, organization
, hangout FROM GANGSTER WHERE (id=?)
22:44:31,644 DEBUG [GangsterEJB] Executing SQL: SELECT name, nick_name, badness, organization
, hangout FROM GANGSTER WHERE (id=?)
22:44:31,649 DEBUG [GangsterEJB] Executing SQL: SELECT name, nick_name, badness, organization
, hangout FROM GANGSTER WHERE (id=?)
22:44:31,658 DEBUG [GangsterEJB] Executing SQL: SELECT name, nick_name, badness, organization
, hangout FROM GANGSTER WHERE (id=?)
22:44:31,670 INFO  [ReadAheadTest] 
###
########################################################
...
We will revisit this example and explore the output when we discuss the settings for optimized loading.