Package com.google.common.cache

Class CacheStats

  • @GwtCompatible
public final class CacheStats
extends Object
    Statistics about the performance of a Cache. Instances of this class are immutable.

    Cache statistics are incremented according to the following rules:

    • When a cache lookup encounters an existing cache entry hitCount is incremented.
    • When a cache lookup first encounters a missing cache entry, a new entry is loaded.
      • After successfully loading an entry missCount and loadSuccessCount are incremented, and the total loading time, in nanoseconds, is added to totalLoadTime.
      • When an exception is thrown while loading an entry, missCount and loadExceptionCount are incremented, and the total loading time, in nanoseconds, is added to totalLoadTime.
      • Cache lookups that encounter a missing cache entry that is still loading will wait for loading to complete (whether successful or not) and then increment missCount.
    • When an entry is evicted from the cache, evictionCount is incremented.
    • No stats are modified when a cache entry is invalidated or manually removed.
    • No stats are modified by operations invoked on the asMap view of the cache.

    A lookup is specifically defined as an invocation of one of the methods LoadingCache.get(Object), LoadingCache.getUnchecked(Object), Cache.get(Object, Callable), or LoadingCache.getAll(Iterable).

    Since:
    10.0
    Author:
    Charles Fry

    • Constructor Summary

      Constructors 
      Constructor Description
      CacheStats​(long hitCount, long missCount, long loadSuccessCount, long loadExceptionCount, long totalLoadTime, long evictionCount)
      Constructs a new CacheStats instance.

    • Constructor Detail

      • CacheStats

        public CacheStats​(long hitCount,
                  long missCount,
                  long loadSuccessCount,
                  long loadExceptionCount,
                  long totalLoadTime,
                  long evictionCount)
        Constructs a new CacheStats instance.

        Five parameters of the same type in a row is a bad thing, but this class is not constructed by end users and is too fine-grained for a builder.

    • Method Detail

      • requestCount

        public long requestCount()
        Returns the number of times Cache lookup methods have returned either a cached or uncached value. This is defined as hitCount + missCount.

        Note: the values of the metrics are undefined in case of overflow (though it is guaranteed not to throw an exception). If you require specific handling, we recommend implementing your own stats collector.

      • hitCount

        public long hitCount()
        Returns the number of times Cache lookup methods have returned a cached value.

      • hitRate

        public double hitRate()
        Returns the ratio of cache requests which were hits. This is defined as hitCount / requestCount, or 1.0 when requestCount == 0. Note that hitRate + missRate =~ 1.0.

      • missCount

        public long missCount()
        Returns the number of times Cache lookup methods have returned an uncached (newly loaded) value, or null. Multiple concurrent calls to Cache lookup methods on an absent value can result in multiple misses, all returning the results of a single cache load operation.

      • missRate

        public double missRate()
        Returns the ratio of cache requests which were misses. This is defined as missCount / requestCount, or 0.0 when requestCount == 0. Note that hitRate + missRate =~ 1.0. Cache misses include all requests which weren't cache hits, including requests which resulted in either successful or failed loading attempts, and requests which waited for other threads to finish loading. It is thus the case that missCount >= loadSuccessCount + loadExceptionCount. Multiple concurrent misses for the same key will result in a single load operation.

      • loadCount

        public long loadCount()
        Returns the total number of times that Cache lookup methods attempted to load new values. This includes both successful load operations and those that threw exceptions. This is defined as loadSuccessCount + loadExceptionCount.

        Note: the values of the metrics are undefined in case of overflow (though it is guaranteed not to throw an exception). If you require specific handling, we recommend implementing your own stats collector.

      • loadSuccessCount

        public long loadSuccessCount()
        Returns the number of times Cache lookup methods have successfully loaded a new value. This is usually incremented in conjunction with missCount, though missCount is also incremented when an exception is encountered during cache loading (see loadExceptionCount). Multiple concurrent misses for the same key will result in a single load operation. This may be incremented not in conjunction with missCount if the load occurs as a result of a refresh or if the cache loader returned more items than was requested. missCount may also be incremented not in conjunction with this (nor loadExceptionCount) on calls to getIfPresent.

      • loadExceptionCount

        public long loadExceptionCount()
        Returns the number of times Cache lookup methods threw an exception while loading a new value. This is usually incremented in conjunction with missCount, though missCount is also incremented when cache loading completes successfully (see loadSuccessCount). Multiple concurrent misses for the same key will result in a single load operation. This may be incremented not in conjunction with missCount if the load occurs as a result of a refresh or if the cache loader returned more items than was requested. missCount may also be incremented not in conjunction with this (nor loadSuccessCount) on calls to getIfPresent.

      • loadExceptionRate

        public double loadExceptionRate()
        Returns the ratio of cache loading attempts which threw exceptions. This is defined as loadExceptionCount / (loadSuccessCount + loadExceptionCount), or 0.0 when loadSuccessCount + loadExceptionCount == 0.

        Note: the values of the metrics are undefined in case of overflow (though it is guaranteed not to throw an exception). If you require specific handling, we recommend implementing your own stats collector.

      • totalLoadTime

        public long totalLoadTime()
        Returns the total number of nanoseconds the cache has spent loading new values. This can be used to calculate the miss penalty. This value is increased every time loadSuccessCount or loadExceptionCount is incremented.

      • averageLoadPenalty

        public double averageLoadPenalty()
        Returns the average time spent loading new values. This is defined as totalLoadTime / (loadSuccessCount + loadExceptionCount).

        Note: the values of the metrics are undefined in case of overflow (though it is guaranteed not to throw an exception). If you require specific handling, we recommend implementing your own stats collector.

      • evictionCount

        public long evictionCount()
        Returns the number of times an entry has been evicted. This count does not include manual invalidations.

      • minus

        public CacheStats minus​(CacheStats other)
        Returns a new CacheStats representing the difference between this CacheStats and other. Negative values, which aren't supported by CacheStats will be rounded up to zero.

      • plus

        public CacheStats plus​(CacheStats other)
        Returns a new CacheStats representing the sum of this CacheStats and other.

        Note: the values of the metrics are undefined in case of overflow (though it is guaranteed not to throw an exception). If you require specific handling, we recommend implementing your own stats collector.

        Since:
        11.0