/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.cassandra.utils;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.util.Arrays;
import java.util.concurrent.atomic.AtomicLongArray;
import org.apache.cassandra.io.ICompactSerializer;
public class EstimatedHistogram
{
public static EstimatedHistogramSerializer serializer = new EstimatedHistogramSerializer();
/**
* The series of values to which the counts in `buckets` correspond:
* 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 17, 20, etc.
* Thus, a `buckets` of [0, 0, 1, 10] would mean we had seen one value of 3 and 10 values of 4.
*
* The series starts at 1 and grows by 1.2 each time (rounding and removing duplicates). It goes from 1
* to around 36M by default (creating 90+1 buckets), which will give us timing resolution from microseconds to
* 36 seconds, with less precision as the numbers get larger.
*
* Each bucket represents values from (previous bucket offset, current offset].
*/
private long[] bucketOffsets;
// buckets is one element longer than bucketOffsets -- the last element is values greater than the last offset
final AtomicLongArray buckets;
public EstimatedHistogram()
{
this(90);
}
public EstimatedHistogram(int bucketCount)
{
makeOffsets(bucketCount);
buckets = new AtomicLongArray(bucketOffsets.length + 1);
}
public EstimatedHistogram(long[] offsets, long[] bucketData)
{
assert bucketData.length == offsets.length +1;
bucketOffsets = offsets;
buckets = new AtomicLongArray(bucketData);
}
private void makeOffsets(int size)
{
bucketOffsets = new long[size];
long last = 1;
bucketOffsets[0] = last;
for (int i = 1; i < size; i++)
{
long next = Math.round(last * 1.2);
if (next == last)
next++;
bucketOffsets[i] = next;
last = next;
}
}
/**
* @return the histogram values corresponding to each bucket index
*/
public long[] getBucketOffsets()
{
return bucketOffsets;
}
/**
* Increments the count of the bucket closest to n, rounding UP.
* @param n
*/
public void add(long n)
{
int index = Arrays.binarySearch(bucketOffsets, n);
if (index < 0)
{
// inexact match, take the first bucket higher than n
index = -index - 1;
}
// else exact match; we're good
buckets.incrementAndGet(index);
}
/**
* @return the count in the given bucket
*/
long get(int bucket)
{
return buckets.get(bucket);
}
/**
* @param reset: zero out buckets afterwards if true
* @return a long[] containing the current histogram buckets
*/
public long[] getBuckets(boolean reset)
{
long[] rv = new long[buckets.length()];
for (int i = 0; i < buckets.length(); i++)
rv[i] = buckets.get(i);
if (reset)
for (int i = 0; i < buckets.length(); i++)
buckets.set(i, 0L);
return rv;
}
/**
* @return the smallest value that could have been added to this histogram
*/
public long min()
{
for (int i = 0; i < buckets.length(); i++)
{
if (buckets.get(i) > 0)
return i == 0 ? 0 : 1 + bucketOffsets[i - 1];
}
return 0;
}
/**
* @return the largest value that could have been added to this histogram. If the histogram
* overflowed, returns Long.MAX_VALUE.
*/
public long max()
{
int lastBucket = buckets.length() - 1;
if (buckets.get(lastBucket) > 0)
return Long.MAX_VALUE;
for (int i = lastBucket - 1; i >= 0; i--)
{
if (buckets.get(i) > 0)
return bucketOffsets[i];
}
return 0;
}
/**
* @return the mean histogram value (average of bucket offsets, weighted by count)
* @throws IllegalStateException if any values were greater than the largest bucket threshold
*/
public long mean()
{
int lastBucket = buckets.length() - 1;
if (buckets.get(lastBucket) > 0)
throw new IllegalStateException("Unable to compute ceiling for max when histogram overflowed");
long elements = 0;
long sum = 0;
for (int i = 0; i < lastBucket; i++)
{
elements += buckets.get(i);
sum += buckets.get(i) * bucketOffsets[i];
}
return (long) Math.ceil((double) sum / elements);
}
/**
* @return true if this histogram has overflowed -- that is, a value larger than our largest bucket could bound was added
*/
public boolean isOverflowed()
{
return buckets.get(buckets.length() - 1) > 0;
}
public static class EstimatedHistogramSerializer implements ICompactSerializer<EstimatedHistogram>
{
public void serialize(EstimatedHistogram eh, DataOutputStream dos) throws IOException
{
long[] offsets = eh.getBucketOffsets();
long[] buckets = eh.getBuckets(false);
dos.writeInt(buckets.length);
for (int i = 0; i < buckets.length; i++)
{
dos.writeLong(offsets[i == 0 ? 0 : i - 1]);
dos.writeLong(buckets[i]);
}
}
public EstimatedHistogram deserialize(DataInputStream dis) throws IOException
{
int size = dis.readInt();
long[] offsets = new long[size - 1];
long[] buckets = new long[size];
for (int i = 0; i < size; i++) {
offsets[i == 0 ? 0 : i - 1] = dis.readLong();
buckets[i] = dis.readLong();
}
return new EstimatedHistogram(offsets, buckets);
}
}
}