Persistent aware KieSession not using Pessimistic Lock during transactions

Question

I am using Drools with Spring Boot 2.3 and I have implemented the persistent aware KieSession, in which MySQL is used for storing the session. I have successfully integrated the default EntityManagerFactory of Spring Boot with Drools but my problem is with transactions. By default, Drools uses Optimistic Lock during transactions but it allows us to use the Pessimistic Lock as well, which is what I want. Now while firing rules, Drools persists/updates the KieSession in MySQL with the following query:

update SessionInfo set lastModificationDate=?, rulesByteArray=?, startDate=?, OPTLOCK=? where id=? and OPTLOCK=?

Now the above statement is executed twice if I do not use transactions using the @Transactional annotation in the method, and if @Transactional is used then the above statement is executed only once after firing the rules.

Now, if I manually change the value of the OPTLOCK field then Drools throws an exception:

javax.persistence.OptimisticLockException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect) : [org.drools.persistence.info.SessionInfo#1]

followed by:

Caused by: org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect) : [org.drools.persistence.info.SessionInfo#1]

I am unable to post the entire Stacktrace due to text length limitations here. The entire stacktrace can be viewed in this GitHub project.

I am not sure whether Drools is using the Pessimistic Lock as defined in the environment. About my session implementation, I want to have a single KieSession since I am using KieSession as a Bean.

Below is my implementation:

The configuration class:

@Configuration
public class DynamicDroolsConfig {

    private KieServices kieServices;
    private KieFileSystem kieFileSystem;

    @Autowired
    private PersistentSessionDAO persistentSessionDAO;
    @PersistenceUnit
    private EntityManagerFactory entityManagerFactory;
    @Autowired
    private PlatformTransactionManager platformTransactionManager;


    @PostConstruct
    private void init() {
        this.kieServices = KieServices.Factory.get();
        this.kieFileSystem = kieServices.newKieFileSystem();
    }

    @Bean
    public KieServices getKieServices() {
        return this.kieServices;
    }

    @Bean
    public KieContainer getKieContainer() {
        kieFileSystem.write(ResourceFactory.newClassPathResource("rules/rules.drl"));
        final KieRepository kieRepository = kieServices.getRepository();
        kieRepository.addKieModule(kieRepository::getDefaultReleaseId);
        KieBuilder kb = kieServices.newKieBuilder(kieFileSystem).buildAll();
        KieModule kieModule = kb.getKieModule();
        return kieServices.newKieContainer(kieModule.getReleaseId());
    }

    @Bean
    public KieFileSystem getFileSystem() {
        return kieFileSystem;
    }

    @Bean
    public KieSession kieSession() {
        List<SessionInfo> sessionDetails = persistentSessionDAO.getSessionDetails();

        if (sessionDetails.size() == 0) {
            return kieServices.getStoreServices().newKieSession(getKieContainer().getKieBase(), null, getEnv());
        } else {
            return kieServices.getStoreServices().loadKieSession(sessionDetails.get(0).getId(), getKieContainer().getKieBase(), null, getEnv());
        }
    }

    private Environment getEnv() {
        Environment env = kieServices.newEnvironment();
        env.set(EnvironmentName.ENTITY_MANAGER_FACTORY, entityManagerFactory);
        env.set(EnvironmentName.TRANSACTION_MANAGER, platformTransactionManager);
        env.set(EnvironmentName.USE_PESSIMISTIC_LOCKING, true);
        env.set(EnvironmentName.USE_PESSIMISTIC_LOCKING_MODE, LockModeType.PESSIMISTIC_FORCE_INCREMENT.name());
        return env;
    }
}

The controller class:

@RestController
public class MyController {

    @Autowired
    private KieSession kieSession;

    @Transactional
    @GetMapping("fire-person")
    public void firePerson() {
        Person person = new Person();
        person.setName("Christy");
        kieSession.insert(person);
        kieSession.fireAllRules();
    }
}

The Fact class

public class Person implements Serializable {

    private String name;
    private int age;
    private String gender;
    private String toCompareName;
    private String toCompareGender;

    // getters and setters
}

The repository interface:

public interface DroolsSessionRepository extends JpaRepository<SessionInfo, Long> {
}

The service class:

@Service
public class PersistentSessionDAO {

    @Autowired
    private DroolsSessionRepository droolsSessionRepository;

    public List<SessionInfo> getSessionDetails() {
        return droolsSessionRepository.findAll();
    }
}

The runner class:

@EntityScan(basePackages = {"com.sam.springdroolspersistence.entity", "org.drools.persistence.info"})
@EnableJpaRepositories
@SpringBootApplication
public class SpringDroolsPersistenceApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringDroolsPersistenceApplication.class, args);
    }
}

The Drools dependencies used:

        <dependency>
            <groupId>org.drools</groupId>
            <artifactId>drools-persistence-jpa</artifactId>
            <version>${drools-version}</version>
        </dependency>

        <dependency>
            <groupId>org.kie</groupId>
            <artifactId>kie-spring</artifactId>
            <version>${drools-version}</version>
        </dependency>

        <dependency>
            <groupId>org.jbpm</groupId>
            <artifactId>jbpm-persistence-jpa</artifactId>
            <version>${drools-version}</version>
        </dependency>

The code implementation can also be found in this GitHub Project. Any kind of help/suggestions will be much appreciated. Thank you.

Answer 1

Pessimistic locking is implemented only in JBPM see here

There's no such functionality in Drools persistence, SessionInfo will always use OptimisticLocking based on JPA's @Version annotation.

If you need such feature, please file a feature request on Drools' Jira