38a54df863
People keep tripping over the old copyrights and copy-pasting them to new files. Search and replace "Cloudius Systems" with "ScyllaDB". Message-Id: <1460013664-25966-1-git-send-email-penberg@scylladb.com>
105 lines
4.5 KiB
C++
105 lines
4.5 KiB
C++
/*
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* Licensed to the Apache Software Foundation (ASF) under one
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* or more contributor license agreements. See the NOTICE file
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* distributed with this work for additional information
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* regarding copyright ownership. The ASF licenses this file
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* to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/*
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* Copyright (C) 2015 ScyllaDB
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*
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* Modified by ScyllaDB
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*/
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/*
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* This file is part of Scylla.
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*
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* Scylla is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Scylla is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "bloom_calculations.hh"
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namespace utils {
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namespace bloom_calculations {
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/**
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* In the following keyspace_name, the row 'i' shows false positive rates if i buckets
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* per element are used. Cell 'j' shows false positive rates if j hash
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* functions are used. The first row is 'i=0', the first column is 'j=0'.
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* Each cell (i,j) the false positive rate determined by using i buckets per
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* element and j hash functions.
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*/
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std::vector<std::vector<double>> probs = {
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{1.0}, // dummy row representing 0 buckets per element
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{1.0, 1.0}, // dummy row representing 1 buckets per element
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{1.0, 0.393, 0.400},
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{1.0, 0.283, 0.237, 0.253},
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{1.0, 0.221, 0.155, 0.147, 0.160},
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{1.0, 0.181, 0.109, 0.092, 0.092, 0.101}, // 5
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{1.0, 0.154, 0.0804, 0.0609, 0.0561, 0.0578, 0.0638},
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{1.0, 0.133, 0.0618, 0.0423, 0.0359, 0.0347, 0.0364},
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{1.0, 0.118, 0.0489, 0.0306, 0.024, 0.0217, 0.0216, 0.0229},
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{1.0, 0.105, 0.0397, 0.0228, 0.0166, 0.0141, 0.0133, 0.0135, 0.0145},
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{1.0, 0.0952, 0.0329, 0.0174, 0.0118, 0.00943, 0.00844, 0.00819, 0.00846}, // 10
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{1.0, 0.0869, 0.0276, 0.0136, 0.00864, 0.0065, 0.00552, 0.00513, 0.00509},
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{1.0, 0.08, 0.0236, 0.0108, 0.00646, 0.00459, 0.00371, 0.00329, 0.00314},
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{1.0, 0.074, 0.0203, 0.00875, 0.00492, 0.00332, 0.00255, 0.00217, 0.00199, 0.00194},
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{1.0, 0.0689, 0.0177, 0.00718, 0.00381, 0.00244, 0.00179, 0.00146, 0.00129, 0.00121, 0.0012},
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{1.0, 0.0645, 0.0156, 0.00596, 0.003, 0.00183, 0.00128, 0.001, 0.000852, 0.000775, 0.000744}, // 15
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{1.0, 0.0606, 0.0138, 0.005, 0.00239, 0.00139, 0.000935, 0.000702, 0.000574, 0.000505, 0.00047, 0.000459},
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{1.0, 0.0571, 0.0123, 0.00423, 0.00193, 0.00107, 0.000692, 0.000499, 0.000394, 0.000335, 0.000302, 0.000287, 0.000284},
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{1.0, 0.054, 0.0111, 0.00362, 0.00158, 0.000839, 0.000519, 0.00036, 0.000275, 0.000226, 0.000198, 0.000183, 0.000176},
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{1.0, 0.0513, 0.00998, 0.00312, 0.0013, 0.000663, 0.000394, 0.000264, 0.000194, 0.000155, 0.000132, 0.000118, 0.000111, 0.000109},
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{1.0, 0.0488, 0.00906, 0.0027, 0.00108, 0.00053, 0.000303, 0.000196, 0.00014, 0.000108, 8.89e-05, 7.77e-05, 7.12e-05, 6.79e-05, 6.71e-05} // 20
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}; // the first column is a dummy column representing K=0.
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/**
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* The optimal number of hashes for a given number of bits per element.
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* These values are automatically calculated from the data above.
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*/
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std::vector<int> initialize_opt_k() {
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std::vector<int> arr;
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arr.resize(probs.size());
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for (auto i = 0; i < int(probs.size()); i++) {
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double min = std::numeric_limits<double>::max();
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auto& prob = probs[i];
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for (auto j = 0; j < int(prob.size()); j++) {
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if (prob[j] < min) {
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min = prob[j];
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arr[i] = std::max(min_k, j);
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}
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}
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}
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return arr;
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}
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std::vector<int> opt_k_per_buckets = initialize_opt_k();
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}
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}
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