具有统计信息的异步 Caffeine 缓存

Question

关注 this 博客 post 关于实现 Caffeine 异步缓存的内容，我们想从缓存中获取统计数据。

我们使用的是 Caffeine2.7.0 版本

但是，AsyncCache 似乎无法访问其统计信息：

private AsyncCache<String, Cat> asyncCache = Caffeine.newBuilder()
        .expireAfterWrite(1, TimeUnit.HOURS)
        .recordStats()
        .maximumSize(100)
        .buildAsync();

private Cache<String, Cat> cache = Caffeine.newBuilder()
        .expireAfterWrite(1, TimeUnit.HOURS)
        .maximumSize(100)
        .recordStats()
        .build();

....

cache.stats(); // this is possible
asyncCache.stats(); // no such method in asyncCache

另外，在查看AsyncCache and comparing it to the Cacheclass的源码时，asyncclass中没有stats()方法。

这有什么原因吗？

Answer 1

AsyncCache 提供了一个 synchronous() 视图来提供一个阻塞直到异步计算完成的缓存。

/**
  * Returns a view of the entries stored in this cache as a synchronous {@link Cache}. A mapping is
  * not present if the value is currently being loaded. Modifications made to the synchronous cache
  * directly affect the asynchronous cache. If a modification is made to a mapping that is
  * currently loading, the operation blocks until the computation completes.
  *
  * @return a thread-safe synchronous view of this cache
  */
Cache<K, V> synchronous();

这可以很方便地执行操作，例如 invalidate(key)，没有异步对应项。它还提供对统计信息和政策元数据的访问。

AsyncCache<Integer, Integer> cache = Caffeine.newBuilder()
    .maximumSize(10_000)
    .recordStats()
    .buildAsync();

// Perform application work
for (int i = 0; i < 4; i++) {
  cache.get(1, key -> key);
}

// Statistics can be queried and reported on
System.out.println(cache.synchronous().stats());

在这种情况下，我们希望第一个未命中加载条目，以便后续查找成功。

CacheStats{hitCount=3, missCount=1, loadSuccessCount=1, loadFailureCount=0, totalLoadTime=8791091, evictionCount=0, evictionWeight=0}

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