Apache Omid TSO 组件源码实现原理解析

thread1
    TSOChannelHandler#channelRead
        AbstractRequestProcessor#timestampRequest 接收 client 请求，创建 RequestEvent 并 publish
thread2
    AbstractRequestProcessor#onEvent 处理 RequestEvent 请求
        AbstractRequestProcessor#handleRequest
            PersistenceProcessorImpl#addTimestampToBatch 创建 PersistEvent,当 batch 满了发送事件
thread3
    PersistenceProcessorHandler#onEvent 持久化事件处理

private void handleCommit(RequestEvent event) throws Exception {
    long startTimestamp = event.getStartTimestamp(); // startTimestamp
    Iterable<Long> writeSet = event.writeSet(); // 写入集，存储的是 cellIds
    Collection<Long> tableIdSet = event.getTableIdSet();
    boolean isCommitRetry = event.isCommitRetry();
    boolean nonEmptyWriteSet = writeSet.iterator().hasNext(); // 检查写集合是否为空，即事务是否有写操作
    if (startTimestamp > lowWatermark &&
        !hasConflictsWithFences(startTimestamp, tableIdSet) &&
        !hasConflictsWithCommittedTransactions(startTimestamp, writeSet)) { // 检查事务是否满足提交条件,通过 hasConflictsWithCommittedTransactions 判断是否有事务写冲突
        // 可以进行事务提交
        long commitTimestamp = timestampOracle.next(); // 获取提交时间戳
        Optional<Long> forwardNewWaterMark = Optional.absent();
        if (nonEmptyWriteSet) { // 写集合非空
            long newLowWatermark = lowWatermark;
            for (long r : writeSet) { // 遍历写集合中的每个元素，更新其最新的写入时间戳，并计算新的低水位线
                long removed = hashmap.putLatestWriteForCell(r, commitTimestamp); // 更新 cellId 对应的 commitTimestamp, 返回之前的 oldest commitTimestamp
                newLowWatermark = Math.max(removed, newLowWatermark); // 更新低水位线
            }
            if (newLowWatermark != lowWatermark) { // 更新低水位线
                lowWatermark = newLowWatermark;
                forwardNewWaterMark = Optional.of(lowWatermark);
            }
        }
        forwardCommit(startTimestamp, commitTimestamp, c, event.getMonCtx(), forwardNewWaterMark);  // 持久化 commit 请求
    } else { // 事务不满足提交条件
        if (isCommitRetry) { // Re-check if it was already committed but the client retried due to a lag replying
            forwardCommitRetry(startTimestamp, c, event.getMonCtx());  // 若是提交重试，再次检查是否已提交以避免因响应延迟导致的重复提交
        } else {
            forwardAbort(startTimestamp, c, event.getMonCtx()); // 否则，中止事务
        }
    }
}

public long set(long key, long value) {
    final int index = index(key); // cellId 取模返回下标，可能会冲突
    int oldestIndex = 0;
    long oldestValue = Long.MAX_VALUE;
    for (int i = 0; i < associativity; ++i) {
        int currIndex = 2 * (index + i); // 计算 key 下标
        if (cache[currIndex] == key) { // 相同事务 cellId, 替换场景
            oldestValue = 0;
            oldestIndex = currIndex;
            break;
        }
        if (cache[currIndex + 1] <= oldestValue) { // 没找到相同的key.通过和 oldestValue 比较会将最小的 timestamp 剔除
            oldestValue = cache[currIndex + 1];
            oldestIndex = currIndex;
        }
    }
    // 替换最旧的键值对，将其更新为新的键值对
    cache[oldestIndex] = key;
    cache[oldestIndex + 1] = value;
    return oldestValue;
}

public long get(long key) {
    final int index = index(key);
    for (int i = 0; i < associativity; ++i) { // associativity 里存储的元素key应该是相同的
        int currIndex = 2 * (index + i); // 计算 key 的下标
        if (cache[currIndex] == key) { // 找到 cache key
            return cache[currIndex + 1]; // 返回对应的 value
        }
    }
    return 0;
}

创建 event,添加到 current batch
如果 current batch is full
    triggerCurrentBatchFlush