CODEWITHSUNDEEP
javaguava
Jenia Be Nice Please
Jenia Be Nice Please

Reputation: 2693

Guava CacheBuilder not clearing cache

I use the CacheBuilder with expireAfterWrite(2000, TimeUnit.Milliseconds). I send 10000 requests to my program and I expect the CacheBuilder to call RemovalListener 10000 times after 2 seconds for each request. I do not observe this behaviour and instead I get RemovalListener called 1 or 2 times.

Can someone please explain to me what CacheBuilder is doing because as I explained above it is doing something totally different from the documentation that Guava is providing.

In the same spirit as above, I use maximumSize(1000) and after sending my program 10000 requests, I expect the RemovalListener to be called 9000 times. But it's called only 1 or 2 times.

How does this module works in reality?

EDIT

I explicitly call clean cleanup each time I receive a request

Upvotes: 1

Views: 755

Answers (1)

Grzegorz Rożniecki
Grzegorz Rożniecki

Reputation: 27995

The removal behavior is documented and works as expected (emphasis mine):

When Does Cleanup Happen?

Caches built with CacheBuilder do not perform cleanup and evict values "automatically," or instantly after a value expires, or anything of the sort. Instead, it performs small amounts of maintenance during write operations, or during occasional read operations if writes are rare.

The reason for this is as follows: if we wanted to perform Cache maintenance continuously, we would need to create a thread, and its operations would be competing with user operations for shared locks. Additionally, some environments restrict the creation of threads, which would make CacheBuilder unusable in that environment.

Instead, we put the choice in your hands. If your cache is high-throughput, then you don't have to worry about performing cache maintenance to clean up expired entries and the like. If your cache does writes only rarely and you don't want cleanup to block cache reads, you may wish to create your own maintenance thread that calls Cache.cleanUp() at regular intervals.

If you want to have more control over the cache and have dedicated executor to take care for calling RemovalListeners, use Caffeine -- a high performance, near optimal caching library based on Java 8 -- which has an API similar to Guava's Cache (same author). Caffeine has more advanced removal handling:

You may specify a removal listener for your cache to perform some operation when an entry is removed, via Caffeine.removalListener(RemovalListener). The RemovalListener gets passed the key, value, and RemovalCause.

Removal listener operations are executed asynchronously using an Executor. The default executor is ForkJoinPool.commonPool() and can be overridden via Caffeine.executor(Executor). When the operation must be performed synchronously with the removal, use CacheWriter instead.

Upvotes: 3

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