【mq读书笔记】如何保证三个消息文件的最终一致性。

考虑转发任务未成功执行，此时消息服务器Broker宕机，导致commitlog，consumeQueue，IndexFile文件数据不一致。

commitlog，consumeQueue遍历每一条消息，将flushedPosition，committedWhere设置到最后一条正常消息处，并删除在这之后的消息，commitlog在不正常停机重启后，重新转发最后一个mappedFile的消息到consumeQueue，等一系列实现

看一下mq关于存储文件的加载流程：

public boolean load() {
        boolean result = true;

        try {
            boolean lastExitOK = !this.isTempFileExist();
            log.info("last shutdown {}", lastExitOK ? "normally" : "abnormally");

            if (null != scheduleMessageService) {
                result = result && this.scheduleMessageService.load();
            }

            // load Commit Log
            result = result && this.commitLog.load();

            // load Consume Queue
            result = result && this.loadConsumeQueue();

            if (result) {
                this.storeCheckpoint =
                    new StoreCheckpoint(StorePathConfigHelper.getStoreCheckpoint(this.messageStoreConfig.getStorePathRootDir()));

                this.indexService.load(lastExitOK);

                this.recover(lastExitOK);

                log.info("load over, and the max phy offset = {}", this.getMaxPhyOffset());
            }
        } catch (Exception e) {
            log.error("load exception", e);
            result = false;
        }

        if (!result) {
            this.allocateMappedFileService.shutdown();
        }

        return result;
    }