问题
Say I have a Cache that is defined like this:
private static Cache<String, Long> alertsUIDCache = CacheBuilder.newBuilder().
expireAfterAccess(60).build();
From what I read (please correct me if I am wrong):
If value is written to Cache at 0:00, it should be moved to "ready to be evicted" status after 60 seconds. The actual removing of the value from the Cache will happen at the next cache modification (what is exactly is cache modification ?). is that right?
Also, I am not sure what the difference between the invalidateAll() and the cleanUp() methods, can someone provide an explanation?
回答1:
first part from this link : How does Guava expire entries in its CacheBuilder?
I'm going to focus on expireAfterAccess, but the procedure for expireAfterWrite is almost identical. In terms of the mechanics, when you specify expireAfterAccess in the CacheBuilder, then each segment of the cache maintains a linked list access queue for entries in order from least-recent-access to most-recent-access. The cache entries are actually themselves nodes in the linked list, so when an entry is accessed, it removes itself from its old position in the access queue, and moves itself to the end of the queue.
second part : from this link : Guava CacheLoader - invalidate does not immediately invalidate entry if both expireAfterWrite and expireAfterAccess are set
invalidate should remove the entry immediately -- not waiting for another query -- and should force the value to get reloaded on the very next query to that key.
cleanUp: Performs any pending maintenance operations needed by the cache. Exactly which activities are performed -- if any -- is implementation-dependent.
from guava documents: https://github.com/google/guava/wiki/CachesExplained
Explicit Removals
At any time, you may explicitly invalidate cache entries rather than waiting for entries to be evicted. This can be done:
individually, using Cache.invalidate(key)
in bulk, using Cache.invalidateAll(keys)
to all entries, using Cache.invalidateAll()
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 schedule regular cache maintenance for a cache which only rarely has writes, just schedule the maintenance using ScheduledExecutorService.
来源：https://stackoverflow.com/questions/41105447/java-google-guava-cache-difference-between-invalidateall-and-cleanup