Per-Node Shared State

Share state between jobs or services on a cluster node.

❗️
This is a legacy Apache Ignite documentation
The new documentation is hosted here: https://ignite.apache.org/docs/latest/

Overview

It is often useful to share a state between different compute jobs or different deployed services. For this purpose, Ignite provides a shared concurrent node-local-map available on each node.

IgniteCluster cluster = ignite.cluster();

ConcurrentMap<String, Integer> nodeLocalMap = cluster.nodeLocalMap();

Node-local values are similar to thread locals in that these values are not distributed and kept only on the local node. Node-local data can be used by compute jobs to share the state between executions. It can also be used by deployed services.

Example

As an example, let's create a job which increments a node-local counter every time it executes on some node. This way, the node-local counter on each node will tell us how many times a job had executed on that cluster node.

IgniteCallable<Long> job = new IgniteCallable<Long>() {
  @IgniteInstanceResource
  private Ignite ignite;
  
  @Override 
  public Long call() {                  
    // Get a reference to node local.
    ConcurrentMap<String, AtomicLong> nodeLocalMap = ignite.cluster().nodeLocalMap();

    AtomicLong cntr = nodeLocalMap.get("counter");

    if (cntr == null) {
      AtomicLong old = nodeLocalMap.putIfAbsent("counter", cntr = new AtomicLong());
      
      if (old != null)
        cntr = old;
    }
    
    return cntr.incrementAndGet();
  }
};

Now let's execute this job 2 times on the same node and make sure that the value of the counter is 2.

ClusterGroup random = ignite.cluster().forRandom();

IgniteCompute compute = ignite.compute(random);

// The first time the counter on the picked node will be initialized to 1.
Long res = compute.call(job);

assert res == 1;

// Now the counter will be incremented and will have value 2.
res = compute.call(job);

assert res == 2;

Updated 4 months ago