order

This article mainly studies the DLedgerRoleChangeHandler of rocketmq.

DLedgerRoleChangeHandler

rocketmq-all-4.6.0-source-release/broker/src/main/java/org/apache/rocketmq/broker/dledger/DLedgerRoleChangeHandler.java

public class DLedgerRoleChangeHandler implements DLedgerLeaderElector.RoleChangeHandler {

    private static final InternalLogger log = InternalLoggerFactory.getLogger(LoggerName.BROKER_LOGGER_NAME);
    private ExecutorService executorService = Executors.newSingleThreadExecutor(new ThreadFactoryImpl("DLegerRoleChangeHandler_"));
    private BrokerController brokerController;
    private DefaultMessageStore messageStore;
    private DLedgerCommitLog dLedgerCommitLog;
    private DLedgerServer dLegerServer;
    public DLedgerRoleChangeHandler(BrokerController brokerController, DefaultMessageStore messageStore) {
        this.brokerController = brokerController;
        this.messageStore = messageStore;
        this.dLedgerCommitLog = (DLedgerCommitLog) messageStore.getCommitLog();
        this.dLegerServer = dLedgerCommitLog.getdLedgerServer();
    }

    @Override public void handle(long term, MemberState.Role role) {
        Runnable runnable = new Runnable() {
            @Override public void run() {
                long start = System.currentTimeMillis();
                try {
                    boolean succ = true;
                    log.info("Begin handling broker role change term={} role={} currStoreRole={}", term, role, messageStore.getMessageStoreConfig().getBrokerRole());
                    switch (role) {
                        case CANDIDATE:
                            if (messageStore.getMessageStoreConfig().getBrokerRole() != BrokerRole.SLAVE) {
                                brokerController.changeToSlave(dLedgerCommitLog.getId());
                            }
                            break;
                        case FOLLOWER:
                            brokerController.changeToSlave(dLedgerCommitLog.getId());
                            break;
                        case LEADER:
                            while (true) {
                                if (!dLegerServer.getMemberState().isLeader()) {
                                    succ = false;
                                    break;
                                }
                                if (dLegerServer.getdLedgerStore().getLedgerEndIndex() == -1) {
                                    break;
                                }
                                if (dLegerServer.getdLedgerStore().getLedgerEndIndex() == dLegerServer.getdLedgerStore().getCommittedIndex()
                                    && messageStore.dispatchBehindBytes() == 0) {
                                    break;
                                }
                                Thread.sleep(100);
                            }
                            if (succ) {
                                messageStore.recoverTopicQueueTable();
                                brokerController.changeToMaster(BrokerRole.SYNC_MASTER);
                            }
                            break;
                        default:
                            break;
                    }
                    log.info("Finish handling broker role change succ={} term={} role={} currStoreRole={} cost={}", succ, term, role, messageStore.getMessageStoreConfig().getBrokerRole(), DLedgerUtils.elapsed(start));
                } catch (Throwable t) {
                    log.info("[MONITOR]Failed handling broker role change term={} role={} currStoreRole={} cost={}", term, role, messageStore.getMessageStoreConfig().getBrokerRole(), DLedgerUtils.elapsed(start), t);
                }
            }
        };
        executorService.submit(runnable);
    }

    @Override public void startup() {

    }

    @Override public void shutdown() {
        executorService.shutdown();
    }
}

• DLedgerRoleChangeHandler implements the DLedgerLeaderElector.RoleChangeHandler interface, and its handle method submits a runnable to executorService; its shutdown method executes executorService.shutdown(); the runnable method does different things according to MemberState.Role, which happens when role is CANDIDATE and messageStore.getMessageStoreConfig().getBrokerRole() is not SLAVE Execute brokerController.changeToSlave(dLedgerCommitLog.getId()); brokerController.changeToSlave(dLedgerCommitLog.getId()) is executed when role is FOLLOWER; messageStore.recoverTopicQueueTable() and kerController.changeToMaster (BrokerRole.SYNC_MASTER) are executed when role is LEADER

changeToSlave

rocketmq-all-4.6.0-source-release/broker/src/main/java/org/apache/rocketmq/broker/BrokerController.java

public class BrokerController {
	
	//......

    public void changeToSlave(int brokerId) {
        log.info("Begin to change to slave brokerName={} brokerId={}", brokerConfig.getBrokerName(), brokerId);

        //change the role
        brokerConfig.setBrokerId(brokerId == 0 ? 1 : brokerId); //TO DO check
        messageStoreConfig.setBrokerRole(BrokerRole.SLAVE);

        //handle the scheduled service
        try {
            this.messageStore.handleScheduleMessageService(BrokerRole.SLAVE);
        } catch (Throwable t) {
            log.error("[MONITOR] handleScheduleMessageService failed when changing to slave", t);
        }

        //handle the transactional service
        try {
            this.shutdownProcessorByHa();
        } catch (Throwable t) {
            log.error("[MONITOR] shutdownProcessorByHa failed when changing to slave", t);
        }

        //handle the slave synchronise
        handleSlaveSynchronize(BrokerRole.SLAVE);

        try {
            this.registerBrokerAll(true, true, brokerConfig.isForceRegister());
        } catch (Throwable ignored) {

        }
        log.info("Finish to change to slave brokerName={} brokerId={}", brokerConfig.getBrokerName(), brokerId);
    }

	//......
}

• The changeToSlave method mainly executes messageStoreConfig.setBrokerRole(BrokerRole.SLAVE), then shutdownProcessorByHa(), handleSlaveSynchronize(BrokerRole.SLAVE), and registerBrokerAll(true, true, brokerConfig.isForceRegister()).

changeToMaster

rocketmq-all-4.6.0-source-release/broker/src/main/java/org/apache/rocketmq/broker/BrokerController.java

public class BrokerController {
	
	//......

    public void changeToMaster(BrokerRole role) {
        if (role == BrokerRole.SLAVE) {
            return;
        }
        log.info("Begin to change to master brokerName={}", brokerConfig.getBrokerName());

        //handle the slave synchronise
        handleSlaveSynchronize(role);

        //handle the scheduled service
        try {
            this.messageStore.handleScheduleMessageService(role);
        } catch (Throwable t) {
            log.error("[MONITOR] handleScheduleMessageService failed when changing to master", t);
        }

        //handle the transactional service
        try {
            this.startProcessorByHa(BrokerRole.SYNC_MASTER);
        } catch (Throwable t) {
            log.error("[MONITOR] startProcessorByHa failed when changing to master", t);
        }

        //if the operations above are totally successful, we change to master
        brokerConfig.setBrokerId(0); //TO DO check
        messageStoreConfig.setBrokerRole(role);

        try {
            this.registerBrokerAll(true, true, brokerConfig.isForceRegister());
        } catch (Throwable ignored) {

        }
        log.info("Finish to change to master brokerName={}", brokerConfig.getBrokerName());
    }

	//......
}

• The changeToMaster method executes handleSlaveSynchronize, startProcessorByHa(BrokerRole.SYNC_MASTER), and registerBrokerAll(true, true, brokerConfig.isForceRegister())

Summary

DLedgerRoleChangeHandler implements the DLedgerLeaderElector.RoleChangeHandler interface, and its handle method submits a runnable to executorService; its shutdown method executes executorService.shutdown(); the runnable method does different things according to MemberState.Role, which happens when role is CANDIDATE and messageStore.getMessageStoreConfig().getBrokerRole() is not SLAVE Execute brokerController.changeToSlave(dLedgerCommitLog.getId()); brokerController.changeToSlave(dLedgerCommitLog.getId()) is executed when role is FOLLOWER; messageStore.recoverTopicQueueTable() and kerController.changeToMaster (BrokerRole.SYNC_MASTER) are executed when role is LEADER

doc

• DLedgerRoleChangeHandler