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/*
* Copyright 2014 Ben Manes. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.github.benmanes.caffeine.cache.stats;
import java.util.Objects;
import org.checkerframework.checker.index.qual.NonNegative;
import org.checkerframework.checker.nullness.qual.Nullable;
import com.github.benmanes.caffeine.cache.Cache;
import com.github.benmanes.caffeine.cache.LoadingCache;
import com.google.errorprone.annotations.Immutable;
/**
* Statistics about the performance of a {@link Cache}.
*
* Cache statistics are incremented according to the following rules:
*
* - When a cache lookup encounters an existing cache entry {@code hitCount} is incremented.
*
- When a cache lookup first encounters a missing cache entry, a new entry is loaded.
*
* - After successfully loading an entry {@code missCount} and {@code loadSuccessCount} are
* incremented, and the total loading time, in nanoseconds, is added to
* {@code totalLoadTime}.
*
- When an exception is thrown while loading an entry or if the loaded value is {code null},
* {@code missCount} and {@code loadFailureCount} are incremented, and the total loading
* time, in nanoseconds, is added to {@code 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 {@code missCount}.
*
* - When an entry is computed through the {@linkplain Cache#asMap asMap} the
* {@code loadSuccessCount} or {@code loadFailureCount} is incremented.
*
- When an entry is evicted from the cache, {@code evictionCount} is incremented and the
* weight added to {@code evictionWeight}.
*
- No stats are modified when a cache entry is invalidated or manually removed.
*
- No stats are modified by non-computing operations invoked on the
* {@linkplain Cache#asMap asMap} view of the cache.
*
*
* A lookup is specifically defined as an invocation of one of the methods
* {@link LoadingCache#get(Object)}, {@link Cache#get(Object, java.util.function.Function)}, or
* {@link LoadingCache#getAll(Iterable)}.
*
* This is a value-based class; use of identity-sensitive operations (including reference
* equality ({@code ==}), identity hash code, or synchronization) on instances of {@code CacheStats}
* may have unpredictable results and should be avoided.
*
* @author [email protected] (Ben Manes)
*/
@Immutable
public final class CacheStats {
private static final CacheStats EMPTY_STATS = CacheStats.of(0L, 0L, 0L, 0L, 0L, 0L, 0L);
private final long hitCount;
private final long missCount;
private final long loadSuccessCount;
private final long loadFailureCount;
private final long totalLoadTime;
private final long evictionCount;
private final long evictionWeight;
private CacheStats(@NonNegative long hitCount, @NonNegative long missCount,
@NonNegative long loadSuccessCount, @NonNegative long loadFailureCount,
@NonNegative long totalLoadTime, @NonNegative long evictionCount,
@NonNegative long evictionWeight) {
if ((hitCount < 0) || (missCount < 0) || (loadSuccessCount < 0) || (loadFailureCount < 0)
|| (totalLoadTime < 0) || (evictionCount < 0) || (evictionWeight < 0)) {
throw new IllegalArgumentException();
}
this.hitCount = hitCount;
this.missCount = missCount;
this.loadSuccessCount = loadSuccessCount;
this.loadFailureCount = loadFailureCount;
this.totalLoadTime = totalLoadTime;
this.evictionCount = evictionCount;
this.evictionWeight = evictionWeight;
}
/**
* Returns a {@code CacheStats} representing the specified statistics.
*
* @param hitCount the number of cache hits
* @param missCount the number of cache misses
* @param loadSuccessCount the number of successful cache loads
* @param loadFailureCount the number of failed cache loads
* @param totalLoadTime the total load time (success and failure)
* @param evictionCount the number of entries evicted from the cache
* @param evictionWeight the sum of weights of entries evicted from the cache
* @return a {@code CacheStats} representing the specified statistics
*/
public static CacheStats of(@NonNegative long hitCount, @NonNegative long missCount,
@NonNegative long loadSuccessCount, @NonNegative long loadFailureCount,
@NonNegative long totalLoadTime, @NonNegative long evictionCount,
@NonNegative long evictionWeight) {
// Many 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.
return new CacheStats(hitCount, missCount, loadSuccessCount,
loadFailureCount, totalLoadTime, evictionCount, evictionWeight);
}
/**
* Returns a statistics instance where no cache events have been recorded.
*
* @return an empty statistics instance
*/
public static CacheStats empty() {
return EMPTY_STATS;
}
/**
* Returns the number of times {@link Cache} lookup methods have returned either a cached or
* uncached value. This is defined as {@code 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.
*
* @return the {@code hitCount + missCount}
*/
public @NonNegative long requestCount() {
return saturatedAdd(hitCount, missCount);
}
/**
* Returns the number of times {@link Cache} lookup methods have returned a cached value.
*
* @return the number of times {@link Cache} lookup methods have returned a cached value
*/
public @NonNegative long hitCount() {
return hitCount;
}
/**
* Returns the ratio of cache requests which were hits. This is defined as
* {@code hitCount / requestCount}, or {@code 1.0} when {@code requestCount == 0}. Note that
* {@code hitRate + missRate =~ 1.0}.
*
* @return the ratio of cache requests which were hits
*/
public @NonNegative double hitRate() {
long requestCount = requestCount();
return (requestCount == 0) ? 1.0 : (double) hitCount / requestCount;
}
/**
* Returns the number of times {@link Cache} lookup methods have returned an uncached (newly
* loaded) value, or null. Multiple concurrent calls to {@link Cache} lookup methods on an absent
* value can result in multiple misses, all returning the results of a single cache load
* operation.
*
* @return the number of times {@link Cache} lookup methods have returned an uncached (newly
* loaded) value, or null
*/
public @NonNegative long missCount() {
return missCount;
}
/**
* Returns the ratio of cache requests which were misses. This is defined as
* {@code missCount / requestCount}, or {@code 0.0} when {@code requestCount == 0}.
* Note that {@code 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 {@code missCount >= loadSuccessCount + loadFailureCount}. Multiple
* concurrent misses for the same key will result in a single load operation.
*
* @return the ratio of cache requests which were misses
*/
public @NonNegative double missRate() {
long requestCount = requestCount();
return (requestCount == 0) ? 0.0 : (double) missCount / requestCount;
}
/**
* Returns the total number of times that {@link 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 {@code loadSuccessCount + loadFailureCount}.
*
* 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.
*
* @return the {@code loadSuccessCount + loadFailureCount}
*/
public @NonNegative long loadCount() {
return saturatedAdd(loadSuccessCount, loadFailureCount);
}
/**
* Returns the number of times {@link Cache} lookup methods have successfully loaded a new value.
* This is always incremented in conjunction with {@link #missCount}, though {@code missCount}
* is also incremented when an exception is encountered during cache loading (see
* {@link #loadFailureCount}). Multiple concurrent misses for the same key will result in a
* single load operation.
*
* @return the number of times {@link Cache} lookup methods have successfully loaded a new value
*/
public @NonNegative long loadSuccessCount() {
return loadSuccessCount;
}
/**
* Returns the number of times {@link Cache} lookup methods failed to load a new value, either
* because no value was found or an exception was thrown while loading. This is always incremented
* in conjunction with {@code missCount}, though {@code missCount} is also incremented when cache
* loading completes successfully (see {@link #loadSuccessCount}). Multiple concurrent misses for
* the same key will result in a single load operation.
*
* @return the number of times {@link Cache} lookup methods failed to load a new value
*/
public @NonNegative long loadFailureCount() {
return loadFailureCount;
}
/**
* Returns the ratio of cache loading attempts which threw exceptions. This is defined as
* {@code loadFailureCount / (loadSuccessCount + loadFailureCount)}, or {@code 0.0} when
* {@code loadSuccessCount + loadFailureCount == 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.
*
* @return the ratio of cache loading attempts which threw exceptions
*/
public @NonNegative double loadFailureRate() {
long totalLoadCount = saturatedAdd(loadSuccessCount, loadFailureCount);
return (totalLoadCount == 0) ? 0.0 : (double) loadFailureCount / totalLoadCount;
}
/**
* 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 {@code loadSuccessCount}
* or {@code loadFailureCount} is incremented.
*
* @return the total number of nanoseconds the cache has spent loading new values
*/
public @NonNegative long totalLoadTime() {
return totalLoadTime;
}
/**
* Returns the average number of nanoseconds spent loading new values. This is defined as
* {@code totalLoadTime / (loadSuccessCount + loadFailureCount)}.
*
* 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.
*
* @return the average number of nanoseconds spent loading new values
*/
public @NonNegative double averageLoadPenalty() {
long totalLoadCount = saturatedAdd(loadSuccessCount, loadFailureCount);
return (totalLoadCount == 0) ? 0.0 : (double) totalLoadTime / totalLoadCount;
}
/**
* Returns the number of times an entry has been evicted. This count does not include manual
* {@linkplain Cache#invalidate invalidations}.
*
* @return the number of times an entry has been evicted
*/
public @NonNegative long evictionCount() {
return evictionCount;
}
/**
* Returns the sum of weights of evicted entries. This total does not include manual
* {@linkplain Cache#invalidate invalidations}.
*
* @return the sum of weights of evicted entities
*/
public @NonNegative long evictionWeight() {
return evictionWeight;
}
/**
* Returns a new {@code CacheStats} representing the difference between this {@code CacheStats}
* and {@code other}. Negative values, which aren't supported by {@code CacheStats} will be
* rounded up to zero.
*
* @param other the statistics to subtract with
* @return the difference between this instance and {@code other}
*/
public CacheStats minus(CacheStats other) {
return CacheStats.of(
Math.max(0L, hitCount - other.hitCount),
Math.max(0L, missCount - other.missCount),
Math.max(0L, loadSuccessCount - other.loadSuccessCount),
Math.max(0L, loadFailureCount - other.loadFailureCount),
Math.max(0L, totalLoadTime - other.totalLoadTime),
Math.max(0L, evictionCount - other.evictionCount),
Math.max(0L, evictionWeight - other.evictionWeight));
}
/**
* Returns a new {@code CacheStats} representing the sum of this {@code CacheStats} and
* {@code 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.
*
* @param other the statistics to add with
* @return the sum of the statistics
*/
public CacheStats plus(CacheStats other) {
return CacheStats.of(
saturatedAdd(hitCount, other.hitCount),
saturatedAdd(missCount, other.missCount),
saturatedAdd(loadSuccessCount, other.loadSuccessCount),
saturatedAdd(loadFailureCount, other.loadFailureCount),
saturatedAdd(totalLoadTime, other.totalLoadTime),
saturatedAdd(evictionCount, other.evictionCount),
saturatedAdd(evictionWeight, other.evictionWeight));
}
/**
* Returns the sum of {@code a} and {@code b} unless it would overflow or underflow in which case
* {@code Long.MAX_VALUE} or {@code Long.MIN_VALUE} is returned, respectively.
*/
@SuppressWarnings("ShortCircuitBoolean")
private static long saturatedAdd(long a, long b) {
long naiveSum = a + b;
if (((a ^ b) < 0) | ((a ^ naiveSum) >= 0)) {
// If a and b have different signs or a has the same sign as the result then there was no
// overflow, return.
return naiveSum;
}
// we did over/under flow, if the sign is negative we should return MAX otherwise MIN
return Long.MAX_VALUE + ((naiveSum >>> (Long.SIZE - 1)) ^ 1);
}
@Override
public int hashCode() {
return Objects.hash(hitCount, missCount, loadSuccessCount,
loadFailureCount, totalLoadTime, evictionCount, evictionWeight);
}
@Override
public boolean equals(@Nullable Object o) {
if (o == this) {
return true;
} else if (!(o instanceof CacheStats)) {
return false;
}
CacheStats other = (CacheStats) o;
return hitCount == other.hitCount
&& missCount == other.missCount
&& loadSuccessCount == other.loadSuccessCount
&& loadFailureCount == other.loadFailureCount
&& totalLoadTime == other.totalLoadTime
&& evictionCount == other.evictionCount
&& evictionWeight == other.evictionWeight;
}
@Override
public String toString() {
return getClass().getSimpleName() + '{'
+ "hitCount=" + hitCount + ", "
+ "missCount=" + missCount + ", "
+ "loadSuccessCount=" + loadSuccessCount + ", "
+ "loadFailureCount=" + loadFailureCount + ", "
+ "totalLoadTime=" + totalLoadTime + ", "
+ "evictionCount=" + evictionCount + ", "
+ "evictionWeight=" + evictionWeight
+ '}';
}
}