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.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      double averageLoadPenalty()
      Returns the average time spent loading new values.
      boolean equals(@Nullable Object object)
      Indicates whether some other object is "equal to" this one.
      long evictionCount()
      Returns the number of times an entry has been evicted.
      int hashCode()
      Returns a hash code value for the object.
      long hitCount()
      Returns the number of times Cache lookup methods have returned a cached value.
      double hitRate()
      Returns the ratio of cache requests which were hits.
      long loadCount()
      Returns the total number of times that Cache lookup methods attempted to load new values.
      long loadExceptionCount()
      Returns the number of times Cache lookup methods threw an exception while loading a new value.
      double loadExceptionRate()
      Returns the ratio of cache loading attempts which threw exceptions.
      long loadSuccessCount()
      Returns the number of times Cache lookup methods have successfully loaded a new value.
      CacheStats minus(CacheStats other)
      Returns a new CacheStats representing the difference between this CacheStats and other.
      long missCount()
      Returns the number of times Cache lookup methods have returned an uncached (newly loaded) value, or null.
      double missRate()
      Returns the ratio of cache requests which were misses.
      CacheStats plus(CacheStats other)
      Returns a new CacheStats representing the sum of this CacheStats and other.
      long requestCount()
      Returns the number of times Cache lookup methods have returned either a cached or uncached value.
      String toString()
      Returns a string representation of the object.
      long totalLoadTime()
      Returns the total number of nanoseconds the cache has spent loading new values.

    • 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, as well as 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

      • hashCode

        public int hashCode()
        Description copied from class: java.lang.Object
        Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.

        The general contract of hashCode is:

        • Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
        • If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
        • It is not required that if two objects are unequal according to the Object.equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.

        As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (The hashCode may or may not be implemented as some function of an object's memory address at some point in time.)

        Overrides:
        hashCode in class Object
        Returns:
        a hash code value for this object.
        See Also:
        Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)

      • equals

        public boolean equals(@Nullable Object object)
        Description copied from class: java.lang.Object
        Indicates whether some other object is "equal to" this one.

        The equals method implements an equivalence relation on non-null object references:

        • It is reflexive: for any non-null reference value x, x.equals(x) should return true.
        • It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
        • It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
        • It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
        • For any non-null reference value x, x.equals(null) should return false.

        The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

        Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.

        Overrides:
        equals in class Object
        Parameters:
        object - the reference object with which to compare.
        Returns:
        true if this object is the same as the obj argument; false otherwise.
        See Also:
        Object.hashCode(), HashMap

      • toString

        public String toString()
        Description copied from class: java.lang.Object
        Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

        The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of: 

         getClass().getName() + '@' + Integer.toHexString(hashCode())
        Overrides:
        toString in class Object
        Returns:
        a string representation of the object.