Repository information cache map keeps growing until out of memory

[raestio]

Hi,

it looks like there is a bug in RepositoryFactorySupport in combination with QuerydslPredicateExecutor causing the repository information cache map to grow indefinitely, which eventually leads to OOM:

Heap usage in version 3.4.3 (same for 3.4.x):

Heap usage in version 3.3.9:

Steps to reproduce and observed behaviour

I'm attaching a sample application below which is based on Spring Data REST, Spring Data JPA and Querydsl:
spring-repository-cache-map-issue.zip

1. Each HTTP resource request (GET /someItems) will produce a unique entry in repository information cache (repositoryInformationCache)
2. So the number of entries in the map will be equal to number of executed HTTP requests
3. The cacheKey is always unique because its compositionHash is calculated from QuerydslJpaPredicateExecutor which doesn't override hashCode method.
   

The thing is, it behaves the same in version 3.3.9 as well. But there was:

new ConcurrentReferenceHashMap<>(16, ReferenceType.WEAK)

(changed in #3067 - b21b2e8)
so if I understand correctly, the values were always garbage collected because of the WEAK reference type.

[mp911de]

Looks like a regression. It also seems, that we do not benefit from proper caching as the cache keys do not yield many cache hits.

[mp911de]

Two things contribute to cause this problem:

1. Changing the cache map from a map with weak references to one with strong references
2. The actual cause is that during RepositoryInformation creation, we instantiate repository fragments (such as the Querydsl one) and that leads to a different hash code every time.

[mp911de]

That's fixed now. A new snapshot build of 3.4.4-SNAPSHOT is going to be available from repo.spring.io in ~ 30 minutes. Please verify the fix, also, feel free to widely test against this change as it might introduce undesired side-effects.

[raestio]

I've just tested it against 3.4.4-SNAPSHOT. Looks OK, thank you!