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// histogram.h
/**
* Copyright (C) 2008 10gen Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef UTIL_HISTOGRAM_HEADER
#define UTIL_HISTOGRAM_HEADER
#include "../pch.h"
#include <string>
namespace mongo {
using std::string;
/**
* A histogram for a 32-bit integer range.
*/
class Histogram {
public:
/**
* Construct a histogram with 'numBuckets' buckets, optionally
* having the first bucket start at 'initialValue' rather than
* 0. By default, the histogram buckets will be 'bucketSize' wide.
*
* Usage example:
* Histogram::Options opts;
* opts.numBuckets = 3;
* opts.bucketSize = 10;
* Histogram h( opts );
*
* Generates the bucket ranges [0..10],[11..20],[21..max_int]
*
* Alternatively, the flag 'exponential' could be turned on, in
* which case a bucket's maximum value will be
* initialValue + bucketSize * 2 ^ [0..numBuckets-1]
*
* Usage example:
* Histogram::Options opts;
* opts.numBuckets = 4;
* opts.bucketSize = 125;
* opts.exponential = true;
* Histogram h( opts );
*
* Generates the bucket ranges [0..125],[126..250],[251..500],[501..max_int]
*/
struct Options {
boost::uint32_t numBuckets;
boost::uint32_t bucketSize;
boost::uint32_t initialValue;
// use exponential buckets?
bool exponential;
Options()
: numBuckets(0)
, bucketSize(0)
, initialValue(0)
, exponential(false) {}
};
explicit Histogram( const Options& opts );
~Histogram();
/**
* Find the bucket that 'element' falls into and increment its count.
*/
void insert( boost::uint32_t element );
/**
* Render the histogram as string that can be used inside an
* HTML doc.
*/
string toHTML() const;
// testing interface below -- consider it private
/**
* Return the count for the 'bucket'-th bucket.
*/
boost::uint64_t getCount( boost::uint32_t bucket ) const;
/**
* Return the maximum element that would fall in the
* 'bucket'-th bucket.
*/
boost::uint32_t getBoundary( boost::uint32_t bucket ) const;
/**
* Return the number of buckets in this histogram.
*/
boost::uint32_t getBucketsNum() const;
private:
/**
* Returns the bucket where 'element' should fall
* into. Currently assumes that 'element' is greater than the
* minimum 'inialValue'.
*/
boost::uint32_t _findBucket( boost::uint32_t element ) const;
boost::uint32_t _initialValue; // no value lower than it is recorded
boost::uint32_t _numBuckets; // total buckets in the histogram
// all below owned here
boost::uint32_t* _boundaries; // maximum element of each bucket
boost::uint64_t* _buckets; // current count of each bucket
Histogram( const Histogram& );
Histogram& operator=( const Histogram& );
};
} // namespace mongo
#endif // UTIL_HISTOGRAM_HEADER
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