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TCP (Transmission Control Protocol) provides reliable in-order delivery of system messages. Geode uses TCP by default for inter-cache point-to-point messaging. TCP is generally more appropriate than UDP in the following situations:

• Partitioned Data For distributed systems that make extensive use of partitioned regions, TCP is generally a better choice as TCP provides more reliable communications and better performance that UDP.
• Smaller Distributed Systems TCP is preferable to UDP unicast in smaller distributed systems because it implements more reliable communications at the operating system level than UDP and its performance can be substantially faster than UDP.
• Unpredictable Network Loads TCP provides higher levels of fault tolerance and reliability than UDP. While Geode implements retransmission protocols to ensure proper delivery of messages over UDP, it cannot fully compensate for heavy congestion and unpredictable spikes in network loading.

提供了可靠的顺序投递系统消息. 默认情况下, Geode 使用TCP来进行内存交换的 P2P 通信. 在如下的场景, TCP 比 UDP 更合适:

• 对于分布式系统来讲, 分区数据利用分区 Regions, TCP 通常是一个更好地选择, 当 TCP 提供比 UDP更可靠的通信和更好的性能.
• 相对于 UDP Unicast 而言, TCP 更适合中小型分布式系统, 因为它在 OS 层面比 UDP实现了更可靠的通信, 性能比 UDP 更快.
• 未预测的网络负载 TCP 提供比 UDP更高水平的容错和可靠性. 而 Geode 实现了重传协议用于保障 UDP 的可靠传输, 对于重度拥塞和不可预测的峰值, UDP 还是不能完全补偿.

注意: Geode 通常使用 TCP 通信在成员故障检测方面. 在这种情况下, Geode 将尝试建立一个与可疑成员的 TCP/IP 连接, 为了确定是否有成员已经失败Note: Geode always uses TCP communications in member failure detection. In this situation, Geode will attempt to establish a TCP/IP connection with the suspect member in order to determine if the member has failed.

UDP 通信

UDP (User Datagram Protocol) is a connectionless protocol, which uses far fewer resources than TCP. However, UDP has some important limitations that should be factored into a design, namely:

• 64K byte message size limit (including overhead for message headers)
• Markedly slower performance on congested networks
• Limited reliability (Geode compensates through retransmission protocols)

If a Geode system can operate within the limitations of UDP, then it may be a more appropriate choice than TCP in the following situations:

• Replicated Data In systems where most or all of the members use the same replicated regions, UDP multicast may be the most appropriate choice. UDP multicast provides an efficient means of distributing all events for a region. However, when multicast is enabled for a region, all processes in the distributed system receive all events for the region. Therefore, multicast is only suitable when most or all members have the region defined and the members are interested in most or all of the events for the region.

Note: Even when UDP multicast is used for a region, Geode will send unicast messages in some situations. Also, partitioned regions will use UDP unicast for almost all purposes.

• Larger Distributed Systems

As the size of a distributed system increases, the relatively small overhead of UDP makes it the better choice. TCP adds new threads and sockets to every member, causing more overhead as the system grows.

是一个无连接协议, 比 TCP 使用更少的资源. 然而, UDP 有一些重要的限制将会在设计的时候充分考虑:

• 64K 字节消息大小限制 (包括消息头开销)
• 在拥塞网络上有更慢的性能
• 可靠性有限 (Geode 通过'重传协议'来进行补偿)

如果一个Geode 系统能够在 UDP 的限制下运行, 那么在如下的场景下它比 TCP 更合适:

• 同步模式 所有成员或大多数成员都使用相同的复制 Regions, UDP 多播可能是最合适的选择. UDP 多播提供了一个高效分发所有事件的机制. 然而, 当开启多播模式时, 分布式系统中的所有进程都接受 Region 的所有事件. 因此, 多播仅适用于 所有的成员都有 Region 定义, 成员对于所有的Region事件都是感兴趣的.

注意: 甚至 当 UDP 多播被用于一个 Region 时, Geode 将发送单播消息. 同时, 对于大多数操作, Partitioned Regions 将使用 UDP 单播协议.

• 更大的分布式系统规模

随着分布式系统规模的增长, UDP 的开销相对较小是更好的选择. TCP 添加新的线程和套接字到每个成员, 当系统增长时, 导致更多的开销.

注意: 为了配置 Geode 来使用 UDP 对于内存交换的 P2P 消息, 设置如下的 Geode 属性Note: to configure Geode to use UDP for inter-cache point-to-point messaging set the following Geode property: disable-tcp=true

TCP 设置

The following sections provide guidance on TCP settings recommended for Geode下面的章节提供了推荐的 TCP 设置.

Geode 的TCP/IP 通信设置

• Socket Buffer Size In determining buffer size settingsBuffer 大小确定 Buffer 大小设置, the goal is to strike a balance between communication needs and other processing. Larger socket buffers allow Geode members to distribute data and events more quickly, but also reduce the memory available for other tasks. In some cases, particularly when storing very large data objects, finding the right socket buffer size can become critical to system performance.

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