@Documented @Retention(value=RUNTIME) @Target(value={FIELD,METHOD}) public @interface AffinityKeyMapped
@AffinityKeyMapped annotation.
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 Collocation Of Computations And Data.
AffinityKeyMapper, which will be used
if no explicit affinity mapper is specified in cache configuration, will first look
for any field or method annotated with @AffinityKeyMapped 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.
For example, if a Person object is always accessed together with a Company object
for which this person is an employee, then for better performance and scalability it makes sense to
collocate Person objects together with their Company object when storing them in
cache. To achieve that, cache key used to cache Person objects should have a field or method
annotated with @AffinityKeyMapped annotation, which will provide the value of
the company key for which that person works, like so:
public class PersonKey {
// Person ID used to identify a person.
private String personId;
// Company ID which will be used for affinity.
@AffinityKeyMapped
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(..));
AffinityKey class. Here is how a
PersonKey defined above would look using AffinityKey:
Object personKey1 = new AffinityKey("myPersonId1", "myCompanyId");
Object personKey2 = new AffinityKey("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(..));
Collocation Of Computations And Data. In this case,
@AffinityKeyMapped annotation allows to specify a routing affinity key for a
ComputeJob or any other grid computation, such as Runnable,
Callable, or IgniteClosure. 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 LoadBalancingSpi
will be bypassed, and computation will be routed to the grid node where the specified affinity key is cached.
For more information about cache affinity also see AffinityKeyMapper and
AffinityFunction 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.
AffinityFunction,
AffinityKeyMapper,
AffinityKey
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Ignite Fabric : ver. 1.5.11 Release Date : April 8 2016