Gemfire cache throwing PartionedRegionException: Object hashCode inconsistent between peers

Question

When using partitioned caching in gemfire and integrating with spring data using cacheable annotation, it puts the data in cache properly but when retrieving from cache, if the key is on a different partition it is throwing PartionedRegionException saying the hashCode is inconsistent between cache peers. I have overridden equals and hashCode method in the class whose objects are keys for the cache. Any idea where i could be going wrong? The two cache peers are on the same machine. And the locator is started externally. I'm starting cache using the following method.

@Bean
@Primary 
Cache getGemfireCache() {
Cache cache = new CacheFactory().create();
RegionFactory<Object,Object> regionFactory = cache.createRegionFactory(RegionShortcut.PARTITION);
allCacheNames.forEach(cacheName -> regionFactory.create(cacheName));
return cache;
}

Any help would be appreciated.

Thanks!

score 0 · Answer 1 · answered Dec 09 '19 at 23:33

Hmmm.

First, it is hard to describe exactly what problem you are experiencing, but I am nearly certain it has very little to do with Spring Data, or technically, Spring's Cache Abstraction in this case (especially since you mention "caching" using the @Cacheable annotation) than it does with say, Pivotal GemFire itself, or more likely in your application domain model, specifically.

Second, the problem you are experiencing has very little do with your configuration shown above. Essentially, in your configuration, you are creating a "peer" Cache instance along with Regions for each of your caches identified in the @Cacheable annotations declared on your application service methods, which is not particularly interesting in this case.

TIP: Regarding configuration, it would have been better to do this:

@SpringBootApplication
@EnableCachingDefinedRegions
public class MyCachingSpringBootApplication { ... }

See here, here and here for more information.

NOTE: SBDG creates a ClientCache instance by default, not a "peer" Cache instance. If you truly want your Spring application to contain an embedded peer Cache instance and be part of the server cluster, then you would additionally override SBDG's preference of auto-configuring a ClientCache instance by declaring the @PeerCacheApplication annotation. See here for more details.

Next, you mention that you "overrode" equals and hashCode, which seems to suggest you are using some complex key. In general, it is better to keep with simple key types when using Pivotal GemFire, such as Long, Integer, String, etc, for reasons like what you are experiencing.

A better option if you need to influence your partitioning strategy or data organization across the cluster (e.g. perhaps for collocation) is to implement GemFire's PartitionResolver and register it with the PR.

However, it is not uncommon for you cacheable service methods to look like the following:

@Cacheable("CustomersByAccount")
Account findBy(Customer customer) { ... }

As you may well know, the "key" to the @Cacheable "findBy" service method shown above is Customer, which is clearly a complex object and must have a valid equals and hashCode method when used as a key in a GemFire cache Region, used to back the application cache "CustomersByAccount".

A few questions:

Is it possible that A) your complex key's class definition (e.g. like Customer) changed, such as by adding/removing a [new] field or by changing a field type (?) and B) your PARTITION Region backing the cache (e.g. "CustomersByAccount") is persistent?
Is your equals and hashCode methods consistent? That is they declare and use the same fields to determine the result of equals and hashCode?

For example, this would not be valid:

class Customer {

  private Long id;

  private String firstName;
  private String lastName;

  ...

  @Override
  public boolean equals(Object obj) {

    if (this == obj) {
      return true;
    }

    if (!(obj instanceof Customer)) {
      return false;
    }

    Customer that = (Customer) obj;

    return this.id.equals(that.id);
  }

  @Override
  public int hashCode() {

    int hashValue = 17;

    hashValue = 37 * hashValue + this.firstName.hashCode();
    hashValue = 37 * hashValue + this.lastName.hashCode();

    return hashValue;
  }

  ...
}

Or any other combination where equals/hashCode could potentially yield a different result depending on state previously stored in GemFire.

You might also try clearing the cache and rehydrating (eagerly or lazily as necessary), particularly if your class definitions have changed and especially if some of those class types are used as keys.

Also, in general, I would recommend immutable keys as much as possible if it is not possible to strictly stick to simple/scalar types (e.g. like Long or String). Perhaps, if you could share a bit more details into your application domain model classes, such as the types used as keys, along with your use of Spring's Cache Abstraction on your service methods, that might help.

Also, any examples or test cases reproducing the problem are greatly appreciated.

Thanks!

Gemfire cache throwing PartionedRegionException: Object hashCode inconsistent between peers

1 Answers1