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| <div class="subTitle">org.apache.ignite.cache.affinity</div> |
| <h2 title="Annotation Type CacheAffinityKeyMapped" class="title">Annotation Type CacheAffinityKeyMapped</h2> |
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| <pre><a href="http://docs.oracle.com/javase/7/docs/api/java/lang/annotation/Documented.html?is-external=true" title="class or interface in java.lang.annotation">@Documented</a> |
| <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/annotation/Retention.html?is-external=true" title="class or interface in java.lang.annotation">@Retention</a>(<a href="http://docs.oracle.com/javase/7/docs/api/java/lang/annotation/Retention.html?is-external=true#value()" title="class or interface in java.lang.annotation">value</a>=<a href="http://docs.oracle.com/javase/7/docs/api/java/lang/annotation/RetentionPolicy.html?is-external=true#RUNTIME" title="class or interface in java.lang.annotation">RUNTIME</a>) |
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| public @interface <span class="strong">CacheAffinityKeyMapped</span></pre> |
| <div class="block">Optional annotation to specify custom key-to-node affinity. Affinity key is a key |
| which will be used to determine a node on which given cache key will be stored. This |
| annotation allows to mark a field or a method in the cache key object that will be |
| used as an affinity key (instead of the entire cache key object that is used for |
| affinity by default). Note that a class can have only one field or method annotated |
| with <code>@CacheAffinityKeyMapped</code> annotation. |
| <p> |
| One of the major use cases for this annotation is the routing of grid computations |
| to the nodes where the data for this computation is cached, the concept |
| otherwise known as <code>Collocation Of Computations And Data</code>. |
| <p> |
| <h1 class="header">Mapping Cache Keys</h1> |
| The default implementation of <a href="../../../../../org/apache/ignite/cache/affinity/CacheAffinityKeyMapper.html" title="interface in org.apache.ignite.cache.affinity"><code>CacheAffinityKeyMapper</code></a>, which will be used |
| if no explicit affinity mapper is specified in cache configuration, will first look |
| for any field or method annotated with <code>@CacheAffinityKeyMapped</code> annotation. |
| If such field or method is not found, then the cache key itself will be used for |
| key-to-node affinity (this means that all objects with the same cache key will always |
| be routed to the same node). If such field or method is found, then the value of this |
| field or method will be used for key-to-node affinity. This allows to specify alternate |
| affinity key, other than the cache key itself, whenever needed. |
| <p> |
| For example, if a <code>Person</code> object is always accessed together with a <code>Company</code> object |
| for which this person is an employee, then for better performance and scalability it makes sense to |
| collocate <code>Person</code> objects together with their <code>Company</code> object when storing them in |
| cache. To achieve that, cache key used to cache <code>Person</code> objects should have a field or method |
| annotated with <code>@CacheAffinityKeyMapped</code> annotation, which will provide the value of |
| the company key for which that person works, like so: |
| <pre name="code" class="java"> |
| public class PersonKey { |
| // Person ID used to identify a person. |
| private String personId; |
| |
| // Company ID which will be used for affinity. |
| @CacheAffinityKeyMapped |
| private String companyId; |
| ... |
| } |
| ... |
| // Instantiate person keys. |
| Object personKey1 = new PersonKey("myPersonId1", "myCompanyId"); |
| Object personKey2 = new PersonKey("myPersonId2", "myCompanyId"); |
| |
| // Both, the company and the person objects will be cached on the same node. |
| cache.put("myCompanyId", new Company(..)); |
| cache.put(personKey1, new Person(..)); |
| cache.put(personKey2, new Person(..)); |
| </pre> |
| <p> |
| <h2 class="header">CacheAffinityKey</h2> |
| For convenience, you can also optionally use <a href="../../../../../org/apache/ignite/cache/affinity/CacheAffinityKey.html" title="class in org.apache.ignite.cache.affinity"><code>CacheAffinityKey</code></a> class. Here is how a |
| <code>PersonKey</code> defined above would look using <a href="../../../../../org/apache/ignite/cache/affinity/CacheAffinityKey.html" title="class in org.apache.ignite.cache.affinity"><code>CacheAffinityKey</code></a>: |
| <pre name="code" class="java"> |
| Object personKey1 = new CacheAffinityKey("myPersonId1", "myCompanyId"); |
| Object personKey2 = new CacheAffinityKey("myPersonId2", "myCompanyId"); |
| |
| // Both, the company and the person objects will be cached on the same node. |
| cache.put(myCompanyId, new Company(..)); |
| cache.put(personKey1, new Person(..)); |
| cache.put(personKey2, new Person(..)); |
| </pre> |
| <p> |
| <h1 class="header">Collocating Computations And Data</h1> |
| It is also possible to route computations to the nodes where the data is cached. This concept |
| is otherwise known as <code>Collocation Of Computations And Data</code>. In this case, |
| <code>@CacheAffinityKeyMapped</code> annotation allows to specify a routing affinity key for a |
| <a href="../../../../../org/apache/ignite/compute/ComputeJob.html" title="interface in org.apache.ignite.compute"><code>ComputeJob</code></a> or any other grid computation, such as <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Runnable.html?is-external=true" title="class or interface in java.lang"><code>Runnable</code></a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Callable.html?is-external=true" title="class or interface in java.util.concurrent"><code>Callable</code></a>, or |
| <a href="../../../../../org/apache/ignite/lang/IgniteClosure.html" title="interface in org.apache.ignite.lang"><code>IgniteClosure</code></a>. It should be attached to a method or field that provides affinity key |
| for the computation. Only one annotation per class is allowed. Whenever such annotation is detected, |
| then <a href="../../../../../org/apache/ignite/spi/loadbalancing/LoadBalancingSpi.html" title="interface in org.apache.ignite.spi.loadbalancing"><code>LoadBalancingSpi</code></a> will be bypassed, and computation will be routed to the grid node |
| where the specified affinity key is cached. You can also use optional <code>@CacheName</code> |
| annotation whenever non-default cache name needs to be specified. |
| <p> |
| Here is how this annotation can be used to route a job to a node where Person object |
| is cached with ID "1234": |
| <pre name="code" class="java"> |
| G.grid().run(new Runnable() { |
| // This annotation is optional. If omitted, then default |
| // no-name cache will be used. |
| @CacheName |
| private String cacheName = "myCache"; |
| |
| // This annotation specifies that computation should be routed |
| // precisely to the node where key '1234' is cached. |
| @CacheAffinityKeyMapped |
| private String personKey = "1234"; |
| |
| @Override public void run() { |
| // Some computation logic here. |
| ... |
| } |
| }; |
| </pre> |
| The same can be achieved by annotating method instead of field as follows: |
| <pre name="code" class="java"> |
| G.grid().run(new Runnable() { |
| @Override public void run() { |
| // Some computation logic here. |
| ... |
| } |
| |
| // This annotation is optional. If omitted, then default |
| // no-name cache will be used. |
| @CacheName |
| public String cacheName() { |
| return "myCache"; |
| } |
| |
| // This annotation specifies that computation should be routed |
| // precisely to the node where key '1234' is cached. |
| @CacheAffinityKeyMapped |
| public String personKey() { |
| return "1234"; |
| } |
| }; |
| </pre> |
| <p> |
| For more information about cache affinity also see <a href="../../../../../org/apache/ignite/cache/affinity/CacheAffinityKeyMapper.html" title="interface in org.apache.ignite.cache.affinity"><code>CacheAffinityKeyMapper</code></a> and |
| <a href="../../../../../org/apache/ignite/cache/affinity/CacheAffinityFunction.html" title="interface in org.apache.ignite.cache.affinity"><code>CacheAffinityFunction</code></a> documentation. |
| Affinity for a key can be found from any node, regardless of whether it has cache started |
| or not. If cache is not started, affinity function will be fetched from the remote node |
| which does have the cache running.</div> |
| <dl><dt><span class="strong">See Also:</span></dt><dd><code>org.apache.ignite.cache.CacheName</code>, |
| <a href="../../../../../org/apache/ignite/cache/affinity/CacheAffinityFunction.html" title="interface in org.apache.ignite.cache.affinity"><code>CacheAffinityFunction</code></a>, |
| <a href="../../../../../org/apache/ignite/cache/affinity/CacheAffinityKeyMapper.html" title="interface in org.apache.ignite.cache.affinity"><code>CacheAffinityKeyMapper</code></a>, |
| <a href="../../../../../org/apache/ignite/cache/affinity/CacheAffinityKey.html" title="class in org.apache.ignite.cache.affinity"><code>CacheAffinityKey</code></a></dd></dl> |
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