fapifta edited a comment on issue #705: HDDS-3249: renew ContainerCache.INSTANCE in order to test it in a fresh state URL: https://github.com/apache/hadoop-ozone/pull/705#issuecomment-603260761 Great, thank you for the follow up. +1 for the current state. (non-binding) I completely agree we can fix this problem by just removing the isfull assertion, as that is testing the LRUMap functionality, and follow up in further tickets for additional improvements. About LoadingCache: LoadingCache is a guava utility, it provides and LRU cache, and provides facilities to create the instances that are cached, and also guava provides facilities to configure how the cache works. What we need to consider before replacing is that why the ContainerCache is implemented in a way where you can not evict a DB instance from the cache if there is a reference for it. Looking at all the usages of BlockUtils getDb and removeDB methods, all the cached instances are accessed for just short term, and even though creating an instance might be costly, with the default 1024 cache size if the LoadingCache evicts the least recently used item when the cache is full, we do not suffer a huge perf hit, while in the current implementation if the cache is full, then we get an exception, so I would definitely trade this off. With LoadingCache which just have a size restriction, we can have the same cache functionality, if we get rid of reference counting which I think we do not need, as we use the instances just for short periods of time, so most of the time they are in the cache with a zero reference count, and can be evicted. If we still want to ensure that in extreme cases when the cache is pressured, and all items in the cache are referenced, we can use weakValues() in the guava cache to prevent eviction in this case, but this does not seem to be relevant based on the usage of the cached items.
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