关于Storm 中Topology的并发度的理解

来自：https://storm.apache.org/documentation/Understanding-the-parallelism-of-a-Storm-topology.html

http://blog.csdn.net/derekjiang/article/details/9040243

概念理解

原文中用了一张图来说明在一个storm cluster中，topology运行时的并发机制。

其实说白了，当一个topology在storm cluster中运行时，它的并发主要跟3个逻辑实体想过：worker，executor 和task

1. Worker 是运行在工作节点上面，被Supervisor守护进程创建的用来干活的进程。每个Worker对应于一个给定topology的全部执行任务的一个子集。反过来说，一个Worker里面不会运行属于不同的topology的执行任务。

2. Executor可以理解成一个Worker进程中的工作线程。一个Executor中只能运行隶属于同一个component（spout/bolt） 的task。一个Worker进程中可以有一个或多个Executor线程。在默认情况下，一个Executor运行一个task。

3. Task则是spout和bolt中具体要干的活了。一个Executor可以负责1个或多个task。每个component（spout/bolt） 的并发度就是这个component对应的task数量。同时，task也是各个节点之间进行grouping（partition）的单位。

并发度的配置

有多种方法可以进行并发度的配置，其优先级如下：

defaults.yaml < storm.yaml < topology 私有配置 < component level（spout/bolt） 的私有配置 

至于具体怎么配置，至今拷贝过来大家看看便知：

设置worker数量

• Description: 在当前storm cluster中给这个topology创建的worker数量
• Configuration option: TOPOLOGY_WORKERS
• How to set in your code (examples):
  • Config#setNumWorkers

设置executor数量

• Description: 给指定component创建的executor数量
• Configuration option: ?
• How to set in your code (examples):
  • TopologyBuilder#setSpout()
  • TopologyBuilder#setBolt()
  • Note that as of Storm 0.8 the parallelism_hint parameter now specifies the initial number of executors (not tasks!) for that bolt.

设置task数量

• Description: 给指定 component 创建的task数量
• Configuration option: TOPOLOGY_TASKS
• How to set in your code (examples):
  • ComponentConfigurationDeclarer#setNumTasks()

Here is an example code snippet to show these settings in practice:

topologyBuilder.setBolt("green-bolt", new GreenBolt(), 2)
               .setNumTasks(4)
               .shuffleGrouping(blue-spout);

一个运行时的topology的例子

 

The GreenBolt was configured as per the code snippet above whereas BlueSpout and YellowBolt only set the parallelism hint (number of executors). Here is the relevant code:

Config conf = new Config();
conf.setNumWorkers(2); // use two worker processes

topologyBuilder.setSpout("blue-spout", new BlueSpout(), 2); // set parallelism hint to 2

topologyBuilder.setBolt("green-bolt", new GreenBolt(), 2)
               .setNumTasks(4)
               .shuffleGrouping("blue-spout");

topologyBuilder.setBolt("yellow-bolt", new YellowBolt(), 6)
               .shuffleGrouping("green-bolt");

StormSubmitter.submitTopology(
        "mytopology",
        conf,
        topologyBuilder.createTopology()
    );

And of course Storm comes with additional configuration settings to control the parallelism of a topology, including:

• TOPOLOGY_MAX_TASK_PARALLELISM: This setting puts a ceiling on the number of executors that can be spawned for a single component. It is typically used during testing to limit the number of threads spawned when running a topology in local mode. You can set this option via e.g. Config#setMaxTaskParallelism().

 

怎么样在运行过程中修改一个topology的并发度

Storm支持在不restart topology的情况下, 动态的改变(增减)worker processes的数目和executors的数目, 称为rebalancing. 

主要有两种方法可以rebalance一个topology:

1. 使用Storm web UI 来 rebalance topology.
2. 使用CLI 工具 rebalance topology，一个例子如下：

# Reconfigure the topology "mytopology" to use 5 worker processes,
# the spout "blue-spout" to use 3 executors and
# the bolt "yellow-bolt" to use 10 executors.

storm rebalance mytopology -n 5 -e blue-spout=3 -e yellow-bolt=10