序

本文主要研究一下servicecomb-saga的alpha-server

启动alpha-server

alpha-server是servicecomb-saga的分布式事务协调中心，采用spring boot开发，可以直接从jar包启动，需要依赖mysql或pg数据库，同时初始化数据。启动命令如下：

java -jar -Dspring.profiles.active=prd \
 alpha-server-0.2.0-exec.jar \
 --spring.datasource.url=jdbc:postgresql://localhost:5432/postgres \
 --spring.datasource.username=postgres \
 --spring.datasource.password=postgres

AlphaConfig

@EntityScan(basePackages = "org.apache.servicecomb.saga.alpha")
@Configuration
class AlphaConfig {
  private final BlockingQueue<Runnable> pendingCompensations = new LinkedBlockingQueue<>();
  private final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);

  @Value("${alpha.compensation.retry.delay:3000}")
  private int delay;

  @Bean
  Map<String, Map<String, OmegaCallback>> omegaCallbacks() {
    return new ConcurrentHashMap<>();
  }

  @Bean
  OmegaCallback omegaCallback(Map<String, Map<String, OmegaCallback>> callbacks) {
    return new PushBackOmegaCallback(pendingCompensations, new CompositeOmegaCallback(callbacks));
  }
  
  @Bean
  TxEventRepository springTxEventRepository(TxEventEnvelopeRepository eventRepo) {
    return new SpringTxEventRepository(eventRepo);
  }

  @Bean
  CommandRepository springCommandRepository(TxEventEnvelopeRepository eventRepo, CommandEntityRepository commandRepository) {
    return new SpringCommandRepository(eventRepo, commandRepository);
  }

  @Bean
  TxTimeoutRepository springTxTimeoutRepository(TxTimeoutEntityRepository timeoutRepo) {
    return new SpringTxTimeoutRepository(timeoutRepo);
  }

  @Bean
  ScheduledExecutorService compensationScheduler() {
    return scheduler;
  }

  @Bean
  GrpcServerConfig grpcServerConfig() { return new GrpcServerConfig(); }

  @Bean
  TxConsistentService txConsistentService(
      @Value("${alpha.event.pollingInterval:500}") int eventPollingInterval,
      GrpcServerConfig serverConfig,
      ScheduledExecutorService scheduler,
      TxEventRepository eventRepository,
      CommandRepository commandRepository,
      TxTimeoutRepository timeoutRepository,
      OmegaCallback omegaCallback,
      Map<String, Map<String, OmegaCallback>> omegaCallbacks) {

    new EventScanner(scheduler,
        eventRepository, commandRepository, timeoutRepository,
        omegaCallback, eventPollingInterval).run();

    TxConsistentService consistentService = new TxConsistentService(eventRepository);

    ServerStartable startable = buildGrpc(serverConfig, consistentService, omegaCallbacks);
    new Thread(startable::start).start();

    return consistentService;
  }

  private ServerStartable buildGrpc(GrpcServerConfig serverConfig, TxConsistentService txConsistentService,
      Map<String, Map<String, OmegaCallback>> omegaCallbacks) {
    return new GrpcStartable(serverConfig,
        new GrpcTxEventEndpointImpl(txConsistentService, omegaCallbacks));
  }

  @PostConstruct
  void init() {
    new PendingTaskRunner(pendingCompensations, delay).run();
  }

  @PreDestroy
  void shutdown() {
    scheduler.shutdownNow();
  }
}

• 这里主要是启动grpc server
• respository部分有SpringCommandRepository、SpringTxEventRepository、SpringTxTimeoutRepository

小结

• 从整个alpha工程结构来看，相对比较粗糙一点，config、repository等类都没有按包名归类
• 另外整个工程没有做成spring-boot-starter，不方便使用jar包嵌入进行扩展，有待改进

doc

• saga-spring-demo