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Queue and Set

In addition to providing standard key-value map-like storage, Ignite also provides an implementation of a fast Distributed Blocking Queue and Distributed Set.

IgniteQueue and IgniteSet, an implementation of java.util.concurrent.BlockingQueue and java.util.Set interface respectively, also support all operations from the java.util.Collection interface. Both types can be created in either collocated or non-collocated mode.

Below is an example of how to create a distributed queue and set.

Queue:

Ignite ignite = Ignition.start();

IgniteQueue<String> queue = ignite.queue("queueName", // Queue name.
        0, // Queue capacity. 0 for an unbounded queue.
        new CollectionConfiguration() // Collection configuration.
);

Set:

Ignite ignite = Ignition.start();

IgniteSet<String> set = ignite.set("setName", // Set name.
        new CollectionConfiguration() // Collection configuration.
);

Collocated vs. Non-Collocated Mode

If you plan to create just a few queues or sets containing lots of data, then you would create them in non-collocated mode. This will make sure that about equal portion of each queue or set will be stored on each cluster node. On the other hand, if you plan to have many queues or sets, relatively small in size (compared to the whole cache), then you would most likely create them in collocated mode. In this mode all queue or set elements will be stored on the same cluster node, but about equal amount of queues/sets will be assigned to every node.

Non-collocated mode only makes sense for and is only supported for PARTITIONED caches.

A collocated queue and set can be created by setting the collocated property of CollectionConfiguration, like so:

Queue:

Ignite ignite = Ignition.start();

CollectionConfiguration colCfg = new CollectionConfiguration();

colCfg.setCollocated(true);

// Create a colocated queue.
IgniteQueue<String> queue = ignite.queue("queueName", 0, colCfg);

Set:

Ignite ignite = Ignition.start();

CollectionConfiguration colCfg = new CollectionConfiguration();

colCfg.setCollocated(true);

// Create a colocated set.
IgniteSet<String> set = ignite.set("setName", colCfg);

Cache Queues and Load Balancing

Given that elements will remain in the queue until someone takes them, and that no two nodes should ever receive the same element from the queue, cache queues can be used as an alternate work distribution and load balancing approach within Ignite.

For example, you could simply add computations, such as instances of IgniteRunnable to a queue, and have threads on remote nodes call IgniteQueue.take() method which will block if queue is empty. Once the take() method will return a job, a thread will process it and call take() again to get the next job. Given this approach, threads on remote nodes will only start working on the next job when they have completed the previous one, hence creating ideally balanced system where every node only takes the number of jobs it can process, and not more.

Collection Configuration

Ignite collections can be in configured in API via CollectionConfiguration (see above examples). The following configuration parameters can be used:

Setter Description Default

Setter	Description	Default
`setCollocated(boolean)`	Sets collocation mode.	`false`
`setCacheMode(CacheMode)`	Sets underlying cache mode (`PARTITIONED`, `REPLICATED` or `LOCAL`).	`PARTITIONED`
`setAtomicityMode(CacheAtomicityMode)`	Sets underlying cache atomicity mode (`ATOMIC` or `TRANSACTIONAL`).	`ATOMIC`
`setOffHeapMaxMemory(long)`	Sets offheap maximum memory size.	`0` (unlimited)
`setBackups(int)`	Sets number of backups.	`0`
`setNodeFilter(IgnitePredicate<ClusterNode>)`	Sets optional predicate specifying on which nodes entries should be stored.

setCollocated(boolean)

Sets collocation mode.

false

setCacheMode(CacheMode)

Sets underlying cache mode (PARTITIONED, REPLICATED or LOCAL).

PARTITIONED

setAtomicityMode(CacheAtomicityMode)

Sets underlying cache atomicity mode (ATOMIC or TRANSACTIONAL).

ATOMIC

setOffHeapMaxMemory(long)

Sets offheap maximum memory size.

0 (unlimited)

setBackups(int)

Sets number of backups.

0

setNodeFilter(IgnitePredicate<ClusterNode>)

Sets optional predicate specifying on which nodes entries should be stored.

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