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/**
* Copyright (C) 2023-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include <algorithm>
#include <iostream>
#include "mongo/db/pipeline/percentile_algo_tdigest.h"
#include "mongo/db/exec/document_value/value.h"
#include "mongo/db/query/query_knobs_gen.h"
#include "mongo/util/assert_util.h"
namespace mongo {
class TDigestDistributedClassic : public TDigest, public PartialPercentile<Value> {
constexpr static size_t kNegInfCountOffset = 0;
constexpr static size_t kPosInfCountOffset = 1;
constexpr static size_t kMinOffset = 2;
constexpr static size_t kMaxOffset = 3;
constexpr static size_t kCentroidsOffset = 4;
public:
TDigestDistributedClassic(ScalingFunction k_limit, int delta) : TDigest(k_limit, delta) {}
/**
* Serialize the digest's state into a flat array of doubles:
* [negInfCount, posInfCount, min, max, c0.weight, c0.mean, c1.weight, c1.weight, ...]
*/
Value serialize() final {
flushBuffer();
std::vector<double> flattened(kCentroidsOffset, 0);
flattened[kNegInfCountOffset] = _negInfCount;
flattened[kPosInfCountOffset] = _posInfCount;
flattened[kMinOffset] = _min;
flattened[kMaxOffset] = _max;
flattened.reserve(kCentroidsOffset + 2 * _centroids.size());
for (const Centroid& c : _centroids) {
flattened.push_back(c.weight);
flattened.push_back(c.mean);
}
return Value(std::vector<Value>(flattened.begin(), flattened.end()));
}
/*
* 'partial' is expected to be an array, created by the 'serialize()' above.
*/
void combine(const Value& partial) final {
tassert(7492700,
"TDigest should have been serialized into an array of even size",
partial.isArray() && (partial.getArrayLength() % 2 == 0));
if (partial.getArrayLength() == 0) {
return; // the other t-digest was empty, nothing to do here
}
tassert(7492701,
"Serialized array of non-empty TDigest must contain the min of required elements",
partial.getArrayLength() >= kCentroidsOffset);
const auto& other = partial.getArray();
const int64_t negInfCount = other[kNegInfCountOffset].coerceToLong();
const int64_t posInfCount = other[kPosInfCountOffset].coerceToLong();
const double min = other[kMinOffset].coerceToDouble();
const double max = other[kMaxOffset].coerceToDouble();
std::vector<Centroid> centroids;
centroids.reserve((other.size() - kCentroidsOffset) / 2);
for (size_t i = kCentroidsOffset; i < other.size(); i += 2) {
centroids.push_back({other[i].coerceToDouble(), other[i + 1].coerceToDouble()});
}
merge(TDigest{negInfCount, posInfCount, min, max, centroids, _k_limit, _delta});
}
};
std::unique_ptr<PercentileAlgorithm> createTDigestDistributedClassic() {
return std::make_unique<TDigestDistributedClassic>(TDigest::k2_limit,
internalQueryTdigestDelta.load());
}
} // namespace mongo
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