Tag: websphere

Websphere, SQL Server and Deadlock

How avoid deadlock with Websphere and SQL Server

When you create a datasource in Websphere for a SQL Server database, the default isolation level is Repeatable Read. At first it seems the best choice, but repeatable read as isolation level means the presence of table lock, and with table lock, a deadlock can happen at any time!

For example, considere this application stack:

Java 8
Spring Boot 2.4.1
Websphere 8.5.5
SQL Server 2008

If you need a transaction with REQUIRES_NEW propagation, a deadlock can happen if you are going to update the same tables in the parent and child transaction. This because the isolation level is Repeatable Read.

The solution is to relax the isolation level to Read Committed. You avoid deadlock and with hibernate optimistic lock, there is no possibility to miss information.

To set the isolation level of a datasource in Websphere, you have to navigate the path:

Data sources > [datasource name] > Custom properties

and set

webSphereDefaultIsolationLevel=2

where 2 means Read Committed.

That’s what you need to avoid deadlock!

And remember, if you need a pessimistic lock, with JPA is simple to set table lock for a single query (see for example my previous post about it).

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Howto install web application with Spring Roo 2.0 on Websphere 8.5.5

Install web application with Spring Roo 2.0.0.RC1 on Websphere 8.5.5.12

To install spring roo 2.0.0.RC1 on Websphere 8.5.5.12 you have to solve some problems. The environment is as follows:

  • Ubuntu 15.04 (GNU/Linux 3.19.0-15-generic x86_64)
  • IBM J9 VM (build 2.8, JRE 1.8.0 Linux amd64-64 Compressed References 20170419_34
  • Spring Roo 2.0.0.RC1
  • Websphere 8.5.5.12

JPA problem

The first problem is the JPA compatibility. Roo 2.0.0.RC1 uses jpa 2.1 while WAS 8.5.5.12 jpa 2.0.At the start of the application there is such a mistake:

caused by: java.lang.ClassCastException: com.ibm.websphere.persistence.PersistenceProviderImpl incompatible with javax.persistence.spi.PersistenceProvider at javax.persistence.Persistence$1.isLoaded(Persistence.java:110) ~[hibernate-jpa-2.1-api-1.0.0.Final.jar:1.0.0.Final]

To fix this problem, you need to add the HibernatePersistenceProviderResolver class to your project:

HibernatePersistenceProviderResolver.java

and register it in the Application class in the onStartup method

@Override public void onStartup(ServletContext servletContext) throws ServletException {
HibernatePersistenceProviderResolver.register();
super.onStartup(servletContext); }

XML-APIS problem

The second problem is due to xml-apis jar:

Caused by: java.lang.ClassCastException: org.apache.xalan.processor.TransformerFactoryImpl incompatible with javax.xml.transform.TransformerFactory at javax.xml.transform.TransformerFactory.newInstance(Unknown Source) ~[xml-apis-1.4.01.jar:na]

to solve it you need to make an exclusion in pom.xml like this:

<dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-data-jpa</artifactId>
      <exclusions>
      	<exclusion> 
          <groupId>xml-apis</groupId>
          <artifactId>xml-apis</artifactId>
        </exclusion>        
      </exclusions>
    </dependency>

WEBJARS problem

Third issue concerns the webjars protocol:

Caused by: java.lang.NullPointerException at java.io.FilterInputStream.close(FilterInputStream.java:192) at sun.net.www.protocol.jar.JarURLConnection$JarURLInputStream.close(JarURLConnection.java:121) at org.springframework.web.context.support.ServletContextResource.isReadable(ServletContextResource.java:120)

For some reason WAS uses the wsjar protocol instead of jar. Also to access the resources within the jars WAS must have a trailing slash in the path.To solve this, you need to add the following class:

WasWebJarAssetLocator.java

and log it in to WebMvcConfiguration in the addResourceHandlers method

@Override public void addResourceHandlers(ResourceHandlerRegistry registry) { super.addResourceHandlers(registry); registry.addResourceHandler("/webjars/**").addResourceLocations("classpath:/META-INF/resources/webjars/"). resourceChain(false).addResolver(new WebJarsResourceResolver(new WasWebJarAssetLocator())); }

finally adding variable to was (web container custom properties)

com.ibm.ws.webcontainer.SkipMetaInfResourcesProcessing = true

Transactions problem

Another issue with regard to transactions is:

Caused by: java.lang.LinkageError: com/ibm/websphere/uow/UOWSynchronizationRegistry.registerInterposedSynchronization(Ljavax/transaction/Synchronization;)V (loaded from file:/opt/IBM/WebSphere/AppServer/plugins/com.ibm.ws.runtime.jar by org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader@d30c8d80) called from class org.springframework.transaction.jta.WebSphereUowTransactionManager$UOWActionAdapter (loaded from file:/opt/IBM/WebSphere/AppServer/profiles/AppSrv01/installedApps/UBDSK01Node01Cell/uman-1_0_1_war.ear/uman-1.0.1.war/WEB-INF/lib/spring-tx-4.3.3.RELEASE.jar by com.ibm.ws.classloader.CompoundClassLoader@19d0788f[war:uman-1_0_1_war/uman-1.0.1.war]   Local ClassPath: com.ibm.ws.uow.embeddable.EmbeddableUOWManagerImpl.runUnderNewUOW(EmbeddableUOWManagerImpl.java:791) ~[com.ibm.ws.runtime.jar:na] ... 112 common frames omitted

to solve it you have to make some exclusions in the pom. For javax.transaction we make the exclusion and scope provided:

<dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-data-jpa</artifactId>
      <exclusions>
      	<exclusion> 
          <groupId>xml-apis</groupId>
          <artifactId>xml-apis</artifactId>
        </exclusion>
        <exclusion> 
          <groupId>javax.transaction</groupId>
          <artifactId>javax.transaction-api</artifactId>
        </exclusion>
      </exclusions>
    </dependency>
<dependency>
      <groupId>javax.transaction</groupId>
      <artifactId>javax.transaction-api</artifactId>
      <scope>provided</scope>
    </dependency>

for jta we make the exclusion:

<dependency>
      <groupId>io.springlets</groupId>
      <artifactId>springlets-boot-starter-web</artifactId>
      <exclusions>
      	<exclusion>
      		<groupId>javax.transaction</groupId>
    		<artifactId>jta</artifactId>
      	</exclusion>
      </exclusions>
    </dependency>

that’s all.

Having done all this, the application will run smoothly.