/root/doris/be/src/olap/hll.cpp

Source
// 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.

#include "olap/hll.h"

#include <cmath>
#include <map>
#include <ostream>

#include "common/logging.h"
#include "util/coding.h"
#include "util/slice.h"

using std::string;
using std::stringstream;

namespace doris {
#include "common/compile_check_begin.h"
HyperLogLog::HyperLogLog(const Slice& src) {
    // When deserialize return false, we make this object a empty
    if (!deserialize(src)) {
        _type = HLL_DATA_EMPTY;
    }
}

// Convert explicit values to register format, and clear explicit values.
// NOTE: this function won't modify _type.
void HyperLogLog::_convert_explicit_to_register() {
    DCHECK(_type == HLL_DATA_EXPLICIT)
            << "_type(" << _type << ") should be explicit(" << HLL_DATA_EXPLICIT << ")";
    _registers = new uint8_t[HLL_REGISTERS_COUNT];
    memset(_registers, 0, HLL_REGISTERS_COUNT);
    for (auto value : _hash_set) {
        _update_registers(value);
    }
    // clear _hash_set
    vectorized::flat_hash_set<uint64_t>().swap(_hash_set);
}

// Change HLL_DATA_EXPLICIT to HLL_DATA_FULL directly, because HLL_DATA_SPARSE
// is implemented in the same way in memory with HLL_DATA_FULL.
void HyperLogLog::update(uint64_t hash_value) {
    switch (_type) {
    case HLL_DATA_EMPTY:
        _hash_set.insert(hash_value);
        _type = HLL_DATA_EXPLICIT;
        break;
    case HLL_DATA_EXPLICIT:
        if (_hash_set.size() < HLL_EXPLICIT_INT64_NUM) {
            _hash_set.insert(hash_value);
            break;
        }
        _convert_explicit_to_register();
        _type = HLL_DATA_FULL;
        // fall through
    case HLL_DATA_SPARSE:
    case HLL_DATA_FULL:
        _update_registers(hash_value);
        break;
    }
}

void HyperLogLog::merge(const HyperLogLog& other) {
    // fast path
    if (other._type == HLL_DATA_EMPTY) {
        return;
    }
    switch (_type) {
    case HLL_DATA_EMPTY: {
        // _type must change
        _type = other._type;
        switch (other._type) {
        case HLL_DATA_EXPLICIT:
            _hash_set = other._hash_set;
            break;
        case HLL_DATA_SPARSE:
        case HLL_DATA_FULL:
            _registers = new uint8_t[HLL_REGISTERS_COUNT];
            memcpy(_registers, other._registers, HLL_REGISTERS_COUNT);
            break;
        default:
            break;
        }
        break;
    }
    case HLL_DATA_EXPLICIT: {
        switch (other._type) {
        case HLL_DATA_EXPLICIT: {
            // Merge other's explicit values first, then check if the number is exceed
            // HLL_EXPLICIT_INT64_NUM. This is OK because the max value is 2 * 160.
            _hash_set.insert(other._hash_set.begin(), other._hash_set.end());
            if (_hash_set.size() > HLL_EXPLICIT_INT64_NUM) {
                _convert_explicit_to_register();
                _type = HLL_DATA_FULL;
            }
        } break;
        case HLL_DATA_SPARSE:
        case HLL_DATA_FULL:
            _convert_explicit_to_register();
            _merge_registers(other._registers);
            _type = HLL_DATA_FULL;
            break;
        default:
            break;
        }
        break;
    }
    case HLL_DATA_SPARSE:
    case HLL_DATA_FULL: {
        switch (other._type) {
        case HLL_DATA_EXPLICIT:
            for (auto hash_value : other._hash_set) {
                _update_registers(hash_value);
            }
            break;
        case HLL_DATA_SPARSE:
        case HLL_DATA_FULL:
            _merge_registers(other._registers);
            break;
        default:
            break;
        }
        break;
    }
    }
}

size_t HyperLogLog::max_serialized_size() const {
    switch (_type) {
    case HLL_DATA_EMPTY:
    default:
        return 1;
    case HLL_DATA_EXPLICIT:
        return 2 + _hash_set.size() * 8;
    case HLL_DATA_SPARSE:
    case HLL_DATA_FULL:
        return 1 + HLL_REGISTERS_COUNT;
    }
}

size_t HyperLogLog::serialize(uint8_t* dst) const {
    uint8_t* ptr = dst;
    switch (_type) {
    case HLL_DATA_EMPTY:
    default: {
        // When the _type is unknown, which may not happen, we encode it as
        // Empty HyperLogLog object.
        *ptr++ = HLL_DATA_EMPTY;
        break;
    }
    case HLL_DATA_EXPLICIT: {
        DCHECK(_hash_set.size() <= HLL_EXPLICIT_INT64_NUM)
                << "Number of explicit elements(" << _hash_set.size()
                << ") should be less or equal than " << HLL_EXPLICIT_INT64_NUM;
        *ptr++ = _type;
        *ptr++ = (uint8_t)_hash_set.size();
        for (auto hash_value : _hash_set) {
            encode_fixed64_le(ptr, hash_value);
            ptr += 8;
        }
        break;
    }
    case HLL_DATA_SPARSE:
    case HLL_DATA_FULL: {
        uint32_t num_non_zero_registers = 0;
        for (int i = 0; i < HLL_REGISTERS_COUNT; ++i) {
            num_non_zero_registers += (_registers[i] != 0);
        }

        // each register in sparse format will occupy 3bytes, 2 for index and
        // 1 for register value. So if num_non_zero_registers is greater than
        // 4K we use full encode format.
        if (num_non_zero_registers > HLL_SPARSE_THRESHOLD) {
            *ptr++ = HLL_DATA_FULL;
            memcpy(ptr, _registers, HLL_REGISTERS_COUNT);
            ptr += HLL_REGISTERS_COUNT;
        } else {
            *ptr++ = HLL_DATA_SPARSE;
            // 2-5(4 byte): number of registers
            encode_fixed32_le(ptr, num_non_zero_registers);
            ptr += 4;

            for (uint16_t i = 0; i < HLL_REGISTERS_COUNT; ++i) {
                if (_registers[i] == 0) {
                    continue;
                }
                // 2 bytes: register index
                // 1 byte: register value
                encode_fixed16_le(ptr, i);
                ptr += 2;
                *ptr++ = _registers[i];
            }
        }
        break;
    }
    }
    return ptr - dst;
}

bool HyperLogLog::is_valid(const Slice& slice) {
    if (slice.size < 1) {
        return false;
    }
    const uint8_t* ptr = (uint8_t*)slice.data;
    const uint8_t* end = (uint8_t*)slice.data + slice.size;
    auto type = (HllDataType)*ptr++;
    switch (type) {
    case HLL_DATA_EMPTY:
        break;
    case HLL_DATA_EXPLICIT: {
        if ((ptr + 1) > end) {
            return false;
        }
        uint8_t num_explicits = *ptr++;
        ptr += num_explicits * 8;
        break;
    }
    case HLL_DATA_SPARSE: {
        if ((ptr + 4) > end) {
            return false;
        }
        uint32_t num_registers = decode_fixed32_le(ptr);
        ptr += 4 + 3 * num_registers;
        break;
    }
    case HLL_DATA_FULL: {
        ptr += HLL_REGISTERS_COUNT;
        break;
    }
    default:
        return false;
    }
    return ptr == end;
}

// TODO(zc): check input string's length
bool HyperLogLog::deserialize(const Slice& slice) {
    // can be called only when type is empty
    DCHECK(_type == HLL_DATA_EMPTY);

    // NOTE(zc): Don't remove this check unless you known what
    // you are doing. Because of history bug, we ingest some
    // invalid HLL data in storage, which ptr is nullptr.
    // we must handle this case to avoid process crash.
    // This bug is in release 0.10, I think we can remove this
    // in release 0.12 or later.
    if (slice.data == nullptr || slice.size <= 0) {
        return false;
    }
    // check if input length is valid
    if (!is_valid(slice)) {
        return false;
    }

    const uint8_t* ptr = (uint8_t*)slice.data;
    // first byte : type
    _type = (HllDataType)*ptr++;
    switch (_type) {
    case HLL_DATA_EMPTY:
        break;
    case HLL_DATA_EXPLICIT: {
        // 2: number of explicit values
        // make sure that num_explicit is positive
        uint8_t num_explicits = *ptr++;
        // 3+: 8 bytes hash value
        for (int i = 0; i < num_explicits; ++i) {
            _hash_set.insert(decode_fixed64_le(ptr));
            ptr += 8;
        }
        break;
    }
    case HLL_DATA_SPARSE: {
        _registers = new uint8_t[HLL_REGISTERS_COUNT];
        memset(_registers, 0, HLL_REGISTERS_COUNT);
        // 2-5(4 byte): number of registers
        uint32_t num_registers = decode_fixed32_le(ptr);
        ptr += 4;
        for (uint32_t i = 0; i < num_registers; ++i) {
            // 2 bytes: register index
            // 1 byte: register value
            uint16_t register_idx = decode_fixed16_le(ptr);
            ptr += 2;
            _registers[register_idx] = *ptr++;
        }
        break;
    }
    case HLL_DATA_FULL: {
        _registers = new uint8_t[HLL_REGISTERS_COUNT];
        // 2+ : hll register value
        memcpy(_registers, ptr, HLL_REGISTERS_COUNT);
        break;
    }
    default:
        // revert type to EMPTY
        _type = HLL_DATA_EMPTY;
        return false;
    }
    return true;
}

int64_t HyperLogLog::estimate_cardinality() const {
    if (_type == HLL_DATA_EMPTY) {
        return 0;
    }
    if (_type == HLL_DATA_EXPLICIT) {
        return _hash_set.size();
    }

    const int num_streams = HLL_REGISTERS_COUNT;
    // Empirical constants for the algorithm.
    float alpha = 0;

    if (num_streams == 16) {
        alpha = 0.673F;
    } else if (num_streams == 32) {
        alpha = 0.697F;
    } else if (num_streams == 64) {
        alpha = 0.709F;
    } else {
        alpha = 0.7213F / (1 + 1.079F / num_streams);
    }

    float harmonic_mean = 0;
    int num_zero_registers = 0;

    for (int i = 0; i < HLL_REGISTERS_COUNT; ++i) {
        harmonic_mean += powf(2.0F, -_registers[i]);

        if (_registers[i] == 0) {
            ++num_zero_registers;
        }
    }

    harmonic_mean = 1.0F / harmonic_mean;
    double estimate = alpha * num_streams * num_streams * harmonic_mean;
    // according to HyperLogLog current correction, if E is cardinal
    // E =< num_streams * 2.5 , LC has higher accuracy.
    // num_streams * 2.5 < E , HyperLogLog has higher accuracy.
    // Generally , we can use HyperLogLog to produce value as E.
    if (estimate <= num_streams * 2.5 && num_zero_registers != 0) {
        // Estimated cardinality is too low. Hll is too inaccurate here, instead use
        // linear counting.
        estimate = num_streams *
                   log(static_cast<double>(num_streams) / static_cast<double>(num_zero_registers));
    } else if (num_streams == 16384 && estimate < 72000) {
        // when Linear Couint change to HyperLogLog according to HyperLogLog Correction,
        // there are relatively large fluctuations, we fixed the problem refer to redis.
        double bias = 5.9119 * 1.0e-18 * (estimate * estimate * estimate * estimate) -
                      1.4253 * 1.0e-12 * (estimate * estimate * estimate) +
                      1.2940 * 1.0e-7 * (estimate * estimate) - 5.2921 * 1.0e-3 * estimate +
                      83.3216;
        estimate -= estimate * (bias / 100);
    }
    return (int64_t)(estimate + 0.5);
}
#include "common/compile_check_end.h"
} // namespace doris

Coverage Report

Created: 2025-09-12 10:50

Line	Count	Source
1		// Licensed to the Apache Software Foundation (ASF) under one
2		// or more contributor license agreements. See the NOTICE file
3		// distributed with this work for additional information
4		// regarding copyright ownership. The ASF licenses this file
5		// to you under the Apache License, Version 2.0 (the
6		// "License"); you may not use this file except in compliance
7		// with the License. You may obtain a copy of the License at
8		//
9		// http://www.apache.org/licenses/LICENSE-2.0
10		//
11		// Unless required by applicable law or agreed to in writing,
12		// software distributed under the License is distributed on an
13		// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
14		// KIND, either express or implied. See the License for the
15		// specific language governing permissions and limitations
16		// under the License.
17
18		#include "olap/hll.h"
19
20		#include <cmath>
21		#include <map>
22		#include <ostream>
23
24		#include "common/logging.h"
25		#include "util/coding.h"
26		#include "util/slice.h"
27
28		using std::string;
29		using std::stringstream;
30
31		namespace doris {
32		#include "common/compile_check_begin.h"
33	1.25k	HyperLogLog::HyperLogLog(const Slice& src) {
34		// When deserialize return false, we make this object a empty
35	1.25k	if (!deserialize(src)) {
36	3	_type = HLL_DATA_EMPTY;
37	3	}
38	1.25k	}
39
40		// Convert explicit values to register format, and clear explicit values.
41		// NOTE: this function won't modify _type.
42	37	void HyperLogLog::_convert_explicit_to_register() {
43	37	DCHECK(_type == HLL_DATA_EXPLICIT)
44	0	<< "_type(" << _type << ") should be explicit(" << HLL_DATA_EXPLICIT << ")";
45	37	_registers = new uint8_t[HLL_REGISTERS_COUNT];
46	37	memset(_registers, 0, HLL_REGISTERS_COUNT);
47	5.90k	for (auto value : _hash_set) {
48	5.90k	_update_registers(value);
49	5.90k	}
50		// clear _hash_set
51	37	vectorized::flat_hash_set<uint64_t>().swap(_hash_set);
52	37	}
53
54		// Change HLL_DATA_EXPLICIT to HLL_DATA_FULL directly, because HLL_DATA_SPARSE
55		// is implemented in the same way in memory with HLL_DATA_FULL.
56	949k	void HyperLogLog::update(uint64_t hash_value) {
57	949k	switch (_type) {
58	3.84k	case HLL_DATA_EMPTY:
59	3.84k	_hash_set.insert(hash_value);
60	3.84k	_type = HLL_DATA_EXPLICIT;
61	3.84k	break;
62	63.7k	case HLL_DATA_EXPLICIT:
63	63.7k	if (_hash_set.size() < HLL_EXPLICIT_INT64_NUM) {
64	63.7k	_hash_set.insert(hash_value);
65	63.7k	break;
66	63.7k	}
67	35	_convert_explicit_to_register();
68	35	_type = HLL_DATA_FULL;
69		// fall through
70	36	case HLL_DATA_SPARSE:
71	881k	case HLL_DATA_FULL:
72	881k	_update_registers(hash_value);
73	881k	break;
74	949k	}
75	949k	}
76
77	392	void HyperLogLog::merge(const HyperLogLog& other) {
78		// fast path
79	392	if (other._type == HLL_DATA_EMPTY) {
80	0	return;
81	0	}
82	392	switch (_type) {
83	386	case HLL_DATA_EMPTY: {
84		// _type must change
85	386	_type = other._type;
86	386	switch (other._type) {
87	353	case HLL_DATA_EXPLICIT:
88	353	_hash_set = other._hash_set;
89	353	break;
90	24	case HLL_DATA_SPARSE:
91	33	case HLL_DATA_FULL:
92	33	_registers = new uint8_t[HLL_REGISTERS_COUNT];
93	33	memcpy(_registers, other._registers, HLL_REGISTERS_COUNT);
94	33	break;
95	0	default:
96	0	break;
97	386	}
98	386	break;
99	386	}
100	386	case HLL_DATA_EXPLICIT: {
101	3	switch (other._type) {
102	2	case HLL_DATA_EXPLICIT: {
103		// Merge other's explicit values first, then check if the number is exceed
104		// HLL_EXPLICIT_INT64_NUM. This is OK because the max value is 2 * 160.
105	2	_hash_set.insert(other._hash_set.begin(), other._hash_set.end());
106	2	if (_hash_set.size() > HLL_EXPLICIT_INT64_NUM) {
107	1	_convert_explicit_to_register();
108	1	_type = HLL_DATA_FULL;
109	1	}
110	2	} break;
111	0	case HLL_DATA_SPARSE:
112	1	case HLL_DATA_FULL:
113	1	_convert_explicit_to_register();
114	1	_merge_registers(other._registers);
115	1	_type = HLL_DATA_FULL;
116	1	break;
117	0	default:
118	0	break;
119	3	}
120	3	break;
121	3	}
122	3	case HLL_DATA_SPARSE:
123	3	case HLL_DATA_FULL: {
124	3	switch (other._type) {
125	1	case HLL_DATA_EXPLICIT:
126	100	for (auto hash_value : other._hash_set) {
127	100	_update_registers(hash_value);
128	100	}
129	1	break;
130	0	case HLL_DATA_SPARSE:
131	2	case HLL_DATA_FULL:
132	2	_merge_registers(other._registers);
133	2	break;
134	0	default:
135	0	break;
136	3	}
137	3	break;
138	3	}
139	392	}
140	392	}
141
142	6.42k	size_t HyperLogLog::max_serialized_size() const {
143	6.42k	switch (_type) {
144	11	case HLL_DATA_EMPTY:
145	11	default:
146	11	return 1;
147	6.37k	case HLL_DATA_EXPLICIT:
148	6.37k	return 2 + _hash_set.size() * 8;
149	0	case HLL_DATA_SPARSE:
150	32	case HLL_DATA_FULL:
151	32	return 1 + HLL_REGISTERS_COUNT;
152	6.42k	}
153	6.42k	}
154
155	6.42k	size_t HyperLogLog::serialize(uint8_t* dst) const {
156	6.42k	uint8_t* ptr = dst;
157	6.42k	switch (_type) {
158	10	case HLL_DATA_EMPTY:
159	10	default: {
160		// When the _type is unknown, which may not happen, we encode it as
161		// Empty HyperLogLog object.
162	10	*ptr++ = HLL_DATA_EMPTY;
163	10	break;
164	10	}
165	6.37k	case HLL_DATA_EXPLICIT: {
166	6.37k	DCHECK(_hash_set.size() <= HLL_EXPLICIT_INT64_NUM)
167	0	<< "Number of explicit elements(" << _hash_set.size()
168	0	<< ") should be less or equal than " << HLL_EXPLICIT_INT64_NUM;
169	6.37k	*ptr++ = _type;
170	6.37k	*ptr++ = (uint8_t)_hash_set.size();
171	58.7k	for (auto hash_value : _hash_set) {
172	58.7k	encode_fixed64_le(ptr, hash_value);
173	58.7k	ptr += 8;
174	58.7k	}
175	6.37k	break;
176	10	}
177	0	case HLL_DATA_SPARSE:
178	34	case HLL_DATA_FULL: {
179	34	uint32_t num_non_zero_registers = 0;
180	557k	for (int i = 0; i < HLL_REGISTERS_COUNT; ++i) {
181	557k	num_non_zero_registers += (_registers[i] != 0);
182	557k	}
183
184		// each register in sparse format will occupy 3bytes, 2 for index and
185		// 1 for register value. So if num_non_zero_registers is greater than
186		// 4K we use full encode format.
187	34	if (num_non_zero_registers > HLL_SPARSE_THRESHOLD) {
188	9	*ptr++ = HLL_DATA_FULL;
189	9	memcpy(ptr, _registers, HLL_REGISTERS_COUNT);
190	9	ptr += HLL_REGISTERS_COUNT;
191	25	} else {
192	25	*ptr++ = HLL_DATA_SPARSE;
193		// 2-5(4 byte): number of registers
194	25	encode_fixed32_le(ptr, num_non_zero_registers);
195	25	ptr += 4;
196
197	409k	for (uint16_t i = 0; i < HLL_REGISTERS_COUNT; ++i) {
198	409k	if (_registers[i] == 0) {
199	399k	continue;
200	399k	}
201		// 2 bytes: register index
202		// 1 byte: register value
203	9.68k	encode_fixed16_le(ptr, i);
204	9.68k	ptr += 2;
205	9.68k	*ptr++ = _registers[i];
206	9.68k	}
207	25	}
208	34	break;
209	0	}
210	6.42k	}
211	6.42k	return ptr - dst;
212	6.42k	}
213
214	4.04k	bool HyperLogLog::is_valid(const Slice& slice) {
215	4.04k	if (slice.size < 1) {
216	1	return false;
217	1	}
218	4.04k	const uint8_t* ptr = (uint8_t*)slice.data;
219	4.04k	const uint8_t* end = (uint8_t*)slice.data + slice.size;
220	4.04k	auto type = (HllDataType)*ptr++;
221	4.04k	switch (type) {
222	9	case HLL_DATA_EMPTY:
223	9	break;
224	3.99k	case HLL_DATA_EXPLICIT: {
225	3.99k	if ((ptr + 1) > end) {
226	1	return false;
227	1	}
228	3.99k	uint8_t num_explicits = *ptr++;
229	3.99k	ptr += num_explicits * 8;
230	3.99k	break;
231	3.99k	}
232	27	case HLL_DATA_SPARSE: {
233	27	if ((ptr + 4) > end) {
234	1	return false;
235	1	}
236	26	uint32_t num_registers = decode_fixed32_le(ptr);
237	26	ptr += 4 + 3 * num_registers;
238	26	break;
239	27	}
240	11	case HLL_DATA_FULL: {
241	11	ptr += HLL_REGISTERS_COUNT;
242	11	break;
243	27	}
244	3	default:
245	3	return false;
246	4.04k	}
247	4.04k	return ptr == end;
248	4.04k	}
249
250		// TODO(zc): check input string's length
251	4.03k	bool HyperLogLog::deserialize(const Slice& slice) {
252		// can be called only when type is empty
253	4.03k	DCHECK(_type == HLL_DATA_EMPTY);
254
255		// NOTE(zc): Don't remove this check unless you known what
256		// you are doing. Because of history bug, we ingest some
257		// invalid HLL data in storage, which ptr is nullptr.
258		// we must handle this case to avoid process crash.
259		// This bug is in release 0.10, I think we can remove this
260		// in release 0.12 or later.
261	4.03k	if (slice.data == nullptr \|\| slice.size <= 0) {
262	1	return false;
263	1	}
264		// check if input length is valid
265	4.03k	if (!is_valid(slice)) {
266	2	return false;
267	2	}
268
269	4.03k	const uint8_t* ptr = (uint8_t*)slice.data;
270		// first byte : type
271	4.03k	_type = (HllDataType)*ptr++;
272	4.03k	switch (_type) {
273	7	case HLL_DATA_EMPTY:
274	7	break;
275	3.99k	case HLL_DATA_EXPLICIT: {
276		// 2: number of explicit values
277		// make sure that num_explicit is positive
278	3.99k	uint8_t num_explicits = *ptr++;
279		// 3+: 8 bytes hash value
280	45.4k	for (int i = 0; i < num_explicits; ++i) {
281	41.4k	_hash_set.insert(decode_fixed64_le(ptr));
282	41.4k	ptr += 8;
283	41.4k	}
284	3.99k	break;
285	0	}
286	25	case HLL_DATA_SPARSE: {
287	25	_registers = new uint8_t[HLL_REGISTERS_COUNT];
288	25	memset(_registers, 0, HLL_REGISTERS_COUNT);
289		// 2-5(4 byte): number of registers
290	25	uint32_t num_registers = decode_fixed32_le(ptr);
291	25	ptr += 4;
292	9.71k	for (uint32_t i = 0; i < num_registers; ++i) {
293		// 2 bytes: register index
294		// 1 byte: register value
295	9.68k	uint16_t register_idx = decode_fixed16_le(ptr);
296	9.68k	ptr += 2;
297	9.68k	_registers[register_idx] = *ptr++;
298	9.68k	}
299	25	break;
300	0	}
301	9	case HLL_DATA_FULL: {
302	9	_registers = new uint8_t[HLL_REGISTERS_COUNT];
303		// 2+ : hll register value
304	9	memcpy(_registers, ptr, HLL_REGISTERS_COUNT);
305	9	break;
306	0	}
307	0	default:
308		// revert type to EMPTY
309	0	_type = HLL_DATA_EMPTY;
310	0	return false;
311	4.03k	}
312	4.03k	return true;
313	4.03k	}
314
315	1.00k	int64_t HyperLogLog::estimate_cardinality() const {
316	1.00k	if (_type == HLL_DATA_EMPTY) {
317	4	return 0;
318	4	}
319	996	if (_type == HLL_DATA_EXPLICIT) {
320	951	return _hash_set.size();
321	951	}
322
323	45	const int num_streams = HLL_REGISTERS_COUNT;
324		// Empirical constants for the algorithm.
325	45	float alpha = 0;
326
327	45	if (num_streams == 16) {
328	0	alpha = 0.673F;
329	45	} else if (num_streams == 32) {
330	0	alpha = 0.697F;
331	45	} else if (num_streams == 64) {
332	0	alpha = 0.709F;
333	45	} else {
334	45	alpha = 0.7213F / (1 + 1.079F / num_streams);
335	45	}
336
337	45	float harmonic_mean = 0;
338	45	int num_zero_registers = 0;
339
340	737k	for (int i = 0; i < HLL_REGISTERS_COUNT; ++i) {
341	737k	harmonic_mean += powf(2.0F, -_registers[i]);
342
343	737k	if (_registers[i] == 0) {
344	495k	++num_zero_registers;
345	495k	}
346	737k	}
347
348	45	harmonic_mean = 1.0F / harmonic_mean;
349	45	double estimate = alpha * num_streams * num_streams * harmonic_mean;
350		// according to HyperLogLog current correction, if E is cardinal
351		// E =< num_streams * 2.5 , LC has higher accuracy.
352		// num_streams * 2.5 < E , HyperLogLog has higher accuracy.
353		// Generally , we can use HyperLogLog to produce value as E.
354	45	if (estimate <= num_streams * 2.5 && num_zero_registers != 0) {
355		// Estimated cardinality is too low. Hll is too inaccurate here, instead use
356		// linear counting.
357	31	estimate = num_streams *
358	31	log(static_cast<double>(num_streams) / static_cast<double>(num_zero_registers));
359	31	} else if (num_streams == 16384 && estimate < 72000) {
360		// when Linear Couint change to HyperLogLog according to HyperLogLog Correction,
361		// there are relatively large fluctuations, we fixed the problem refer to redis.
362	6	double bias = 5.9119 * 1.0e-18 * (estimate * estimate * estimate * estimate) -
363	6	1.4253 * 1.0e-12 * (estimate * estimate * estimate) +
364	6	1.2940 * 1.0e-7 * (estimate * estimate) - 5.2921 * 1.0e-3 * estimate +
365	6	83.3216;
366	6	estimate -= estimate * (bias / 100);
367	6	}
368	45	return (int64_t)(estimate + 0.5);
369	996	}
370		#include "common/compile_check_end.h"
371		} // namespace doris