HHH-19218 use a stronger hashing function for cache keys

[ben-manes]

Use a stronger hashing function for cache keys to assist in a uniform distribution within the hash table. This mitigates a performance regression in Ehcache due to clustering effects resulting in an O(n) eviction.

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https://hibernate.atlassian.net/browse/HHH-19218

[Sanne]

Hi @ben-manes , thank you so much for caring!

I'm wondering though - while Ehcache is popular in many cases we recommend using caches which are based on your Caffeine library (either directly, such as in Quarkus, or through Infinispan to add distributed capabilities, like in WildFly).
Would you say it's responsibility of the ORM to generate a stronger hash, or should we have such a function applied only in selected integrations?

I'd have no problem in merging this if you believe this is the right level.

[ben-manes]

I would definitely consider this the responsibility of the cache vendor, not a consumer like Hibernate. That is why Java's hash tables use a spreader function where helpful and Ehcache's oversight meant it did not work as they intended. There wasn't a choice since they decided to ignore the issue for over a decade, but thankfully it is fixed in the latest release. I think this can be closed as anyone upgrading to a later Hibernate will surely upgrade Ehcache and be protected. Thanks!

[gavinking]

@ben-manes Thanks so much for following up. 🙏