mapleFU commented on code in PR #2142:
URL: https://github.com/apache/kvrocks/pull/2142#discussion_r1573293664
##########
src/storage/redis_metadata.cc:
##########
@@ -489,3 +489,20 @@ rocksdb::Status SearchMetadata::Decode(Slice *input) {
return rocksdb::Status::OK();
}
+
+void HyperloglogMetadata::Encode(std::string *dst) const {
+ Metadata::Encode(dst);
+ PutFixed8(dst, static_cast<uint8_t>(encode_type_));
+}
+
+rocksdb::Status HyperloglogMetadata::Decode(Slice *input) {
+ if (auto s = Metadata::Decode(input); !s.ok()) {
+ return s;
+ }
+
+ if (!GetFixed8(input, reinterpret_cast<uint8_t *>(&encode_type_))) {
Review Comment:
@PragmaTwice Is this casting a valid cast? Since `encode_type_` supports
less than `uint8_t`'s domain?
##########
src/types/hyperloglog.cc:
##########
@@ -0,0 +1,256 @@
+/*
+ * 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.
+ *
+ */
+
+/* Redis HyperLogLog probabilistic cardinality approximation.
+ * This file implements the algorithm and the exported Redis commands.
+ *
+ * Copyright (c) 2014, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * * Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * * Neither the name of Redis nor the names of its contributors may be used
+ * to endorse or promote products derived from this software without
+ * specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+// NOTE: this file is copy from redis's source: `src/hyperloglog.c`
+
+#include "hyperloglog.h"
+
+#include "murmurhash2.h"
+
+/* Store the value of the register at position 'index' into variable 'val'.
+ * 'registers' is an array of unsigned bytes. */
+void HllDenseGetRegister(uint8_t *val, uint8_t *registers, uint32_t index) {
+ uint32_t byte = index * kHyperLogLogBits / 8;
+ uint8_t fb = index * kHyperLogLogBits & 7;
+ uint8_t fb8 = 8 - fb;
+ uint8_t b0 = registers[byte];
+ uint8_t b1 = registers[byte + 1];
+ *val = ((b0 >> fb) | (b1 << fb8)) & kHyperLogLogRegisterMax;
+}
+
+/* Set the value of the register at position 'index' to 'val'.
+ * 'registers' is an array of unsigned bytes. */
+void HllDenseSetRegister(uint8_t *registers, uint32_t index, uint8_t val) {
+ uint32_t byte = index * kHyperLogLogBits / 8;
+ uint8_t fb = index * kHyperLogLogBits & 7;
+ uint8_t fb8 = 8 - fb;
+ uint8_t v = val;
+ registers[byte] &= ~(kHyperLogLogRegisterMax << fb);
+ registers[byte] |= v << fb;
+ registers[byte + 1] &= ~(kHyperLogLogRegisterMax >> fb8);
+ registers[byte + 1] |= v >> fb8;
+}
+
+/* ========================= HyperLogLog algorithm =========================
*/
+
+/* Given a string element to add to the HyperLogLog, returns the length
+ * of the pattern 000..1 of the element hash. As a side effect
'register_index' is
+ * set which the element hashes to. */
+uint8_t HllPatLen(const std::vector<uint8_t> &element, uint32_t
*register_index) {
+ int elesize = static_cast<int>(element.size());
+ uint64_t hash = 0, bit = 0, index = 0;
+ int count = 0;
+
+ /* Count the number of zeroes starting from bit kHyperLogLogRegisterCount
+ * (that is a power of two corresponding to the first bit we don't use
+ * as index). The max run can be 64-kHyperLogLogRegisterCountPow+1 =
kHyperLogLogHashBitCount+1 bits.
+ *
+ * Note that the final "1" ending the sequence of zeroes must be
+ * included in the count, so if we find "001" the count is 3, and
+ * the smallest count possible is no zeroes at all, just a 1 bit
+ * at the first position, that is a count of 1.
+ *
+ * This may sound like inefficient, but actually in the average case
+ * there are high probabilities to find a 1 after a few iterations. */
+ hash = MurmurHash64A(element.data(), elesize, 0xadc83b19ULL);
+ index = hash & kHyperLogLogRegisterCountMask; /* Register index. */
+ hash >>= kHyperLogLogRegisterCountPow; /* Remove bits used to
address the register. */
+ hash |= ((uint64_t)1 << kHyperLogLogHashBitCount); /* Make sure the loop
terminates
+ and count will be <=
kHyperLogLogHashBitCount+1. */
+ bit = 1;
+ count = 1; /* Initialized to 1 since we count the "00000...1" pattern. */
+ while ((hash & bit) == 0) {
+ count++;
+ bit <<= 1;
+ }
+ *register_index = (int)index;
+ return count;
+}
+
+/* Compute the register histogram in the dense representation. */
+void HllDenseRegHisto(uint8_t *registers, int *reghisto) {
+ /* Redis default is to use 16384 registers 6 bits each. The code works
+ * with other values by modifying the defines, but for our target value
+ * we take a faster path with unrolled loops. */
+ if (kHyperLogLogRegisterCount == 16384 && kHyperLogLogBits == 6) {
+ uint8_t *r = registers;
+ unsigned long r0 = 0, r1 = 0, r2 = 0, r3 = 0, r4 = 0, r5 = 0, r6 = 0, r7 =
0, r8 = 0, r9 = 0, r10 = 0, r11 = 0,
+ r12 = 0, r13 = 0, r14 = 0, r15 = 0;
+ for (auto j = 0; j < 1024; j++) {
Review Comment:
This code is a bit hacking, can we change `63` to `kHyperLogLogRegisterMax` ?
##########
src/types/redis_hyperloglog.cc:
##########
@@ -0,0 +1,154 @@
+/*
+ * 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 "redis_hyperloglog.h"
+
+#include <db_util.h>
+#include <stdint.h>
+
+namespace redis {
+
+rocksdb::Status HyperLogLog::GetMetadata(Database::GetOptions get_options,
const Slice &ns_key,
+ HyperloglogMetadata *metadata) {
+ return Database::GetMetadata(get_options, {kRedisHyperLogLog}, ns_key,
metadata);
+}
+
+/* the max 0 pattern counter of the subset the element belongs to is
incremented if needed */
+rocksdb::Status HyperLogLog::Add(const Slice &user_key, const
std::vector<Slice> &elements, uint64_t *ret) {
+ *ret = 0;
+ std::string ns_key = AppendNamespacePrefix(user_key);
+
+ LockGuard guard(storage_->GetLockManager(), ns_key);
+ HyperloglogMetadata metadata;
+ rocksdb::Status s = GetMetadata(GetOptions(), ns_key, &metadata);
+ if (!s.ok() && !s.IsNotFound()) return s;
+
+ auto batch = storage_->GetWriteBatchBase();
+ WriteBatchLogData log_data(kRedisHyperLogLog);
+ batch->PutLogData(log_data.Encode());
+
+ Bitmap::SegmentCacheStore cache(storage_, metadata_cf_handle_, ns_key,
&metadata);
+ for (const auto &element : elements) {
+ uint32_t register_index = 0;
+ auto ele_str = element.ToString();
+ std::vector<uint8_t> ele(ele_str.begin(), ele_str.end());
+ uint8_t count = HllPatLen(ele, ®ister_index);
+ uint32_t segment_index = register_index /
kHyperLogLogRegisterCountPerSegment;
+ uint32_t register_index_in_segment = register_index %
kHyperLogLogRegisterCountPerSegment;
+
+ std::string *segment = nullptr;
+ auto s = cache.GetMut(segment_index, &segment);
+ if (!s.ok()) return s;
+ if (segment->size() == 0) {
+ segment->resize(kHyperLogLogRegisterBytesPerSegment, 0);
+ }
+
+ uint8_t old_count = 0;
+ HllDenseGetRegister(&old_count, reinterpret_cast<uint8_t
*>(segment->data()), register_index_in_segment);
+ if (count > old_count) {
+ HllDenseSetRegister(reinterpret_cast<uint8_t *>(segment->data()),
register_index_in_segment, count);
+ *ret = 1;
+ }
+ }
+ cache.BatchForFlush(batch);
+ return storage_->Write(storage_->DefaultWriteOptions(),
batch->GetWriteBatch());
+}
+
+rocksdb::Status HyperLogLog::Count(const Slice &user_key, uint64_t *ret) {
+ *ret = 0;
+ std::vector<uint8_t> registers(kHyperLogLogRegisterBytes);
+ auto s = getRegisters(user_key, ®isters);
+ if (!s.ok()) return s;
+ *ret = HllCount(registers);
+ return rocksdb::Status::OK();
+}
+
+rocksdb::Status HyperLogLog::Merge(const std::vector<Slice> &user_keys) {
+ std::vector<uint8_t> max(kHyperLogLogRegisterBytes);
+ for (const auto &user_key : user_keys) {
+ std::vector<uint8_t> registers(kHyperLogLogRegisterBytes);
+ auto s = getRegisters(user_key, ®isters);
+ if (!s.ok()) return s;
+ HllMerge(&max, registers);
+ }
+
+ std::string ns_key = AppendNamespacePrefix(user_keys[0]);
+ LockGuard guard(storage_->GetLockManager(), ns_key);
+ HyperloglogMetadata metadata;
+ rocksdb::Status s = GetMetadata(GetOptions(), ns_key, &metadata);
+ if (!s.ok() && !s.IsNotFound()) return s;
+
+ auto batch = storage_->GetWriteBatchBase();
+ WriteBatchLogData log_data(kRedisHyperLogLog);
+ batch->PutLogData(log_data.Encode());
+
+ Bitmap::SegmentCacheStore cache(storage_, metadata_cf_handle_, ns_key,
&metadata);
+ for (uint32_t segment_index = 0; segment_index < kHyperLogLogSegmentCount;
segment_index++) {
+ std::string *segment = nullptr;
+ s = cache.GetMut(segment_index, &segment);
+ if (!s.ok()) return s;
+ (*segment).assign(reinterpret_cast<const char *>(max.data()) +
segment_index * kHyperLogLogRegisterBytesPerSegment,
+ kHyperLogLogRegisterBytesPerSegment);
+ }
+ cache.BatchForFlush(batch);
+ return storage_->Write(storage_->DefaultWriteOptions(),
batch->GetWriteBatch());
+}
+
+rocksdb::Status HyperLogLog::getRegisters(const Slice &user_key,
std::vector<uint8_t> *registers) {
+ std::string ns_key = AppendNamespacePrefix(user_key);
+
+ HyperloglogMetadata metadata;
+ LatestSnapShot ss(storage_);
+
+ rocksdb::Status s = GetMetadata(Database::GetOptions{ss.GetSnapShot()},
ns_key, &metadata);
+ if (!s.ok()) return s.IsNotFound() ? rocksdb::Status::OK() : s;
+
+ std::string prefix = InternalKey(ns_key, "", metadata.version,
storage_->IsSlotIdEncoded()).Encode();
+ std::string next_version_prefix = InternalKey(ns_key, "", metadata.version +
1, storage_->IsSlotIdEncoded()).Encode();
+
+ rocksdb::ReadOptions read_options = storage_->DefaultScanOptions();
+ read_options.snapshot = ss.GetSnapShot();
+ rocksdb::Slice upper_bound(next_version_prefix);
+ read_options.iterate_upper_bound = &upper_bound;
+
+ auto iter = util::UniqueIterator(storage_, read_options);
+ for (iter->Seek(prefix); iter->Valid() && iter->key().starts_with(prefix);
iter->Next()) {
+ InternalKey ikey(iter->key(), storage_->IsSlotIdEncoded());
+
+ int register_index = std::stoi(ikey.GetSubKey().ToString());
+ if (register_index / kHyperLogLogRegisterCountPerSegment < 0 ||
+ register_index / kHyperLogLogRegisterCountPerSegment >=
kHyperLogLogSegmentCount ||
+ register_index % kHyperLogLogRegisterCountPerSegment != 0) {
+ return rocksdb::Status::Corruption("invalid subkey index: idx=" +
ikey.GetSubKey().ToString());
+ }
+ auto val = iter->value().ToString();
Review Comment:
nit:
```
std::string_view val = iter->value();
```
This can avoid a around of materialize to `std::string`
##########
src/types/redis_hyperloglog.h:
##########
@@ -0,0 +1,41 @@
+/*
+ * 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.
+ *
+ */
+
+#pragma once
+
+#include "hyperloglog.h"
+#include "storage/redis_db.h"
+#include "storage/redis_metadata.h"
+
+namespace redis {
+
+class HyperLogLog : public Database {
+ public:
+ explicit HyperLogLog(engine::Storage *storage, const std::string &ns) :
Database(storage, ns) {}
+ rocksdb::Status Add(const Slice &user_key, const std::vector<Slice>
&elements, uint64_t *ret);
+ rocksdb::Status Count(const Slice &user_key, uint64_t *ret);
+ rocksdb::Status Merge(const std::vector<Slice> &user_keys);
+
+ private:
+ rocksdb::Status GetMetadata(Database::GetOptions get_options, const Slice
&ns_key, HyperloglogMetadata *metadata);
+ rocksdb::Status getRegisters(const Slice &user_key, std::vector<uint8_t>
*registers);
Review Comment:
Nit: you can add a todo, and optimizing the return value for `getRegisters`
##########
src/types/redis_hyperloglog.cc:
##########
@@ -0,0 +1,154 @@
+/*
+ * 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 "redis_hyperloglog.h"
+
+#include <db_util.h>
+#include <stdint.h>
+
+namespace redis {
+
+rocksdb::Status HyperLogLog::GetMetadata(Database::GetOptions get_options,
const Slice &ns_key,
+ HyperloglogMetadata *metadata) {
+ return Database::GetMetadata(get_options, {kRedisHyperLogLog}, ns_key,
metadata);
+}
+
+/* the max 0 pattern counter of the subset the element belongs to is
incremented if needed */
+rocksdb::Status HyperLogLog::Add(const Slice &user_key, const
std::vector<Slice> &elements, uint64_t *ret) {
+ *ret = 0;
+ std::string ns_key = AppendNamespacePrefix(user_key);
+
+ LockGuard guard(storage_->GetLockManager(), ns_key);
+ HyperloglogMetadata metadata;
+ rocksdb::Status s = GetMetadata(GetOptions(), ns_key, &metadata);
+ if (!s.ok() && !s.IsNotFound()) return s;
+
+ auto batch = storage_->GetWriteBatchBase();
+ WriteBatchLogData log_data(kRedisHyperLogLog);
+ batch->PutLogData(log_data.Encode());
+
+ Bitmap::SegmentCacheStore cache(storage_, metadata_cf_handle_, ns_key,
&metadata);
+ for (const auto &element : elements) {
+ uint32_t register_index = 0;
+ auto ele_str = element.ToString();
+ std::vector<uint8_t> ele(ele_str.begin(), ele_str.end());
+ uint8_t count = HllPatLen(ele, ®ister_index);
+ uint32_t segment_index = register_index /
kHyperLogLogRegisterCountPerSegment;
+ uint32_t register_index_in_segment = register_index %
kHyperLogLogRegisterCountPerSegment;
+
+ std::string *segment = nullptr;
+ auto s = cache.GetMut(segment_index, &segment);
+ if (!s.ok()) return s;
+ if (segment->size() == 0) {
Review Comment:
if `segment->size() != 0`, should we check it's size is equal to
`kHyperLogLogRegisterBytesPerSegment` before `HllDenseGetResgister`?
##########
src/types/redis_hyperloglog.cc:
##########
@@ -0,0 +1,154 @@
+/*
+ * 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 "redis_hyperloglog.h"
+
+#include <db_util.h>
+#include <stdint.h>
+
+namespace redis {
+
+rocksdb::Status HyperLogLog::GetMetadata(Database::GetOptions get_options,
const Slice &ns_key,
+ HyperloglogMetadata *metadata) {
+ return Database::GetMetadata(get_options, {kRedisHyperLogLog}, ns_key,
metadata);
+}
+
+/* the max 0 pattern counter of the subset the element belongs to is
incremented if needed */
+rocksdb::Status HyperLogLog::Add(const Slice &user_key, const
std::vector<Slice> &elements, uint64_t *ret) {
+ *ret = 0;
+ std::string ns_key = AppendNamespacePrefix(user_key);
+
+ LockGuard guard(storage_->GetLockManager(), ns_key);
+ HyperloglogMetadata metadata;
+ rocksdb::Status s = GetMetadata(GetOptions(), ns_key, &metadata);
+ if (!s.ok() && !s.IsNotFound()) return s;
+
+ auto batch = storage_->GetWriteBatchBase();
+ WriteBatchLogData log_data(kRedisHyperLogLog);
+ batch->PutLogData(log_data.Encode());
+
+ Bitmap::SegmentCacheStore cache(storage_, metadata_cf_handle_, ns_key,
&metadata);
+ for (const auto &element : elements) {
+ uint32_t register_index = 0;
+ auto ele_str = element.ToString();
+ std::vector<uint8_t> ele(ele_str.begin(), ele_str.end());
+ uint8_t count = HllPatLen(ele, ®ister_index);
+ uint32_t segment_index = register_index /
kHyperLogLogRegisterCountPerSegment;
+ uint32_t register_index_in_segment = register_index %
kHyperLogLogRegisterCountPerSegment;
+
+ std::string *segment = nullptr;
+ auto s = cache.GetMut(segment_index, &segment);
+ if (!s.ok()) return s;
+ if (segment->size() == 0) {
+ segment->resize(kHyperLogLogRegisterBytesPerSegment, 0);
+ }
+
+ uint8_t old_count = 0;
+ HllDenseGetRegister(&old_count, reinterpret_cast<uint8_t
*>(segment->data()), register_index_in_segment);
+ if (count > old_count) {
+ HllDenseSetRegister(reinterpret_cast<uint8_t *>(segment->data()),
register_index_in_segment, count);
+ *ret = 1;
+ }
+ }
+ cache.BatchForFlush(batch);
+ return storage_->Write(storage_->DefaultWriteOptions(),
batch->GetWriteBatch());
+}
+
+rocksdb::Status HyperLogLog::Count(const Slice &user_key, uint64_t *ret) {
+ *ret = 0;
+ std::vector<uint8_t> registers(kHyperLogLogRegisterBytes);
+ auto s = getRegisters(user_key, ®isters);
+ if (!s.ok()) return s;
+ *ret = HllCount(registers);
+ return rocksdb::Status::OK();
+}
+
+rocksdb::Status HyperLogLog::Merge(const std::vector<Slice> &user_keys) {
+ std::vector<uint8_t> max(kHyperLogLogRegisterBytes);
+ for (const auto &user_key : user_keys) {
+ std::vector<uint8_t> registers(kHyperLogLogRegisterBytes);
+ auto s = getRegisters(user_key, ®isters);
+ if (!s.ok()) return s;
+ HllMerge(&max, registers);
+ }
+
+ std::string ns_key = AppendNamespacePrefix(user_keys[0]);
+ LockGuard guard(storage_->GetLockManager(), ns_key);
+ HyperloglogMetadata metadata;
+ rocksdb::Status s = GetMetadata(GetOptions(), ns_key, &metadata);
+ if (!s.ok() && !s.IsNotFound()) return s;
+
+ auto batch = storage_->GetWriteBatchBase();
+ WriteBatchLogData log_data(kRedisHyperLogLog);
+ batch->PutLogData(log_data.Encode());
+
+ Bitmap::SegmentCacheStore cache(storage_, metadata_cf_handle_, ns_key,
&metadata);
+ for (uint32_t segment_index = 0; segment_index < kHyperLogLogSegmentCount;
segment_index++) {
+ std::string *segment = nullptr;
+ s = cache.GetMut(segment_index, &segment);
+ if (!s.ok()) return s;
+ (*segment).assign(reinterpret_cast<const char *>(max.data()) +
segment_index * kHyperLogLogRegisterBytesPerSegment,
+ kHyperLogLogRegisterBytesPerSegment);
+ }
+ cache.BatchForFlush(batch);
+ return storage_->Write(storage_->DefaultWriteOptions(),
batch->GetWriteBatch());
+}
+
+rocksdb::Status HyperLogLog::getRegisters(const Slice &user_key,
std::vector<uint8_t> *registers) {
+ std::string ns_key = AppendNamespacePrefix(user_key);
+
+ HyperloglogMetadata metadata;
+ LatestSnapShot ss(storage_);
+
+ rocksdb::Status s = GetMetadata(Database::GetOptions{ss.GetSnapShot()},
ns_key, &metadata);
+ if (!s.ok()) return s.IsNotFound() ? rocksdb::Status::OK() : s;
+
+ std::string prefix = InternalKey(ns_key, "", metadata.version,
storage_->IsSlotIdEncoded()).Encode();
+ std::string next_version_prefix = InternalKey(ns_key, "", metadata.version +
1, storage_->IsSlotIdEncoded()).Encode();
+
+ rocksdb::ReadOptions read_options = storage_->DefaultScanOptions();
+ read_options.snapshot = ss.GetSnapShot();
+ rocksdb::Slice upper_bound(next_version_prefix);
+ read_options.iterate_upper_bound = &upper_bound;
+
+ auto iter = util::UniqueIterator(storage_, read_options);
+ for (iter->Seek(prefix); iter->Valid() && iter->key().starts_with(prefix);
iter->Next()) {
+ InternalKey ikey(iter->key(), storage_->IsSlotIdEncoded());
+
+ int register_index = std::stoi(ikey.GetSubKey().ToString());
Review Comment:
nit: kvrocks already has parseInt, we can unify using that rather than
`std::stoi`
##########
src/types/redis_hyperloglog.cc:
##########
@@ -0,0 +1,154 @@
+/*
+ * 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 "redis_hyperloglog.h"
+
+#include <db_util.h>
+#include <stdint.h>
+
+namespace redis {
+
+rocksdb::Status HyperLogLog::GetMetadata(Database::GetOptions get_options,
const Slice &ns_key,
+ HyperloglogMetadata *metadata) {
+ return Database::GetMetadata(get_options, {kRedisHyperLogLog}, ns_key,
metadata);
+}
+
+/* the max 0 pattern counter of the subset the element belongs to is
incremented if needed */
+rocksdb::Status HyperLogLog::Add(const Slice &user_key, const
std::vector<Slice> &elements, uint64_t *ret) {
+ *ret = 0;
+ std::string ns_key = AppendNamespacePrefix(user_key);
+
+ LockGuard guard(storage_->GetLockManager(), ns_key);
+ HyperloglogMetadata metadata;
+ rocksdb::Status s = GetMetadata(GetOptions(), ns_key, &metadata);
+ if (!s.ok() && !s.IsNotFound()) return s;
+
+ auto batch = storage_->GetWriteBatchBase();
+ WriteBatchLogData log_data(kRedisHyperLogLog);
+ batch->PutLogData(log_data.Encode());
+
+ Bitmap::SegmentCacheStore cache(storage_, metadata_cf_handle_, ns_key,
&metadata);
+ for (const auto &element : elements) {
+ uint32_t register_index = 0;
+ auto ele_str = element.ToString();
+ std::vector<uint8_t> ele(ele_str.begin(), ele_str.end());
Review Comment:
nit: how about using `std::string_view` here?
##########
src/types/hyperloglog.cc:
##########
@@ -0,0 +1,256 @@
+/*
+ * 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.
+ *
+ */
+
+/* Redis HyperLogLog probabilistic cardinality approximation.
+ * This file implements the algorithm and the exported Redis commands.
+ *
+ * Copyright (c) 2014, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * * Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * * Neither the name of Redis nor the names of its contributors may be used
+ * to endorse or promote products derived from this software without
+ * specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+// NOTE: this file is copy from redis's source: `src/hyperloglog.c`
+
+#include "hyperloglog.h"
+
+#include "murmurhash2.h"
+
+/* Store the value of the register at position 'index' into variable 'val'.
+ * 'registers' is an array of unsigned bytes. */
+void HllDenseGetRegister(uint8_t *val, uint8_t *registers, uint32_t index) {
+ uint32_t byte = index * kHyperLogLogBits / 8;
+ uint8_t fb = index * kHyperLogLogBits & 7;
+ uint8_t fb8 = 8 - fb;
+ uint8_t b0 = registers[byte];
+ uint8_t b1 = registers[byte + 1];
+ *val = ((b0 >> fb) | (b1 << fb8)) & kHyperLogLogRegisterMax;
+}
+
+/* Set the value of the register at position 'index' to 'val'.
+ * 'registers' is an array of unsigned bytes. */
+void HllDenseSetRegister(uint8_t *registers, uint32_t index, uint8_t val) {
+ uint32_t byte = index * kHyperLogLogBits / 8;
+ uint8_t fb = index * kHyperLogLogBits & 7;
+ uint8_t fb8 = 8 - fb;
+ uint8_t v = val;
+ registers[byte] &= ~(kHyperLogLogRegisterMax << fb);
+ registers[byte] |= v << fb;
+ registers[byte + 1] &= ~(kHyperLogLogRegisterMax >> fb8);
+ registers[byte + 1] |= v >> fb8;
+}
+
+/* ========================= HyperLogLog algorithm =========================
*/
+
+/* Given a string element to add to the HyperLogLog, returns the length
+ * of the pattern 000..1 of the element hash. As a side effect
'register_index' is
+ * set which the element hashes to. */
+uint8_t HllPatLen(const std::vector<uint8_t> &element, uint32_t
*register_index) {
+ int elesize = static_cast<int>(element.size());
+ uint64_t hash = 0, bit = 0, index = 0;
+ int count = 0;
+
+ /* Count the number of zeroes starting from bit kHyperLogLogRegisterCount
+ * (that is a power of two corresponding to the first bit we don't use
+ * as index). The max run can be 64-kHyperLogLogRegisterCountPow+1 =
kHyperLogLogHashBitCount+1 bits.
+ *
+ * Note that the final "1" ending the sequence of zeroes must be
+ * included in the count, so if we find "001" the count is 3, and
+ * the smallest count possible is no zeroes at all, just a 1 bit
+ * at the first position, that is a count of 1.
+ *
+ * This may sound like inefficient, but actually in the average case
+ * there are high probabilities to find a 1 after a few iterations. */
+ hash = MurmurHash64A(element.data(), elesize, 0xadc83b19ULL);
+ index = hash & kHyperLogLogRegisterCountMask; /* Register index. */
+ hash >>= kHyperLogLogRegisterCountPow; /* Remove bits used to
address the register. */
+ hash |= ((uint64_t)1 << kHyperLogLogHashBitCount); /* Make sure the loop
terminates
+ and count will be <=
kHyperLogLogHashBitCount+1. */
+ bit = 1;
+ count = 1; /* Initialized to 1 since we count the "00000...1" pattern. */
+ while ((hash & bit) == 0) {
+ count++;
+ bit <<= 1;
+ }
+ *register_index = (int)index;
+ return count;
+}
+
+/* Compute the register histogram in the dense representation. */
+void HllDenseRegHisto(uint8_t *registers, int *reghisto) {
Review Comment:
registers -> const uint8_t*
##########
src/types/hyperloglog.cc:
##########
@@ -0,0 +1,256 @@
+/*
+ * 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.
+ *
+ */
+
+/* Redis HyperLogLog probabilistic cardinality approximation.
+ * This file implements the algorithm and the exported Redis commands.
+ *
+ * Copyright (c) 2014, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * * Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * * Neither the name of Redis nor the names of its contributors may be used
+ * to endorse or promote products derived from this software without
+ * specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+// NOTE: this file is copy from redis's source: `src/hyperloglog.c`
+
+#include "hyperloglog.h"
+
+#include "murmurhash2.h"
+
+/* Store the value of the register at position 'index' into variable 'val'.
+ * 'registers' is an array of unsigned bytes. */
+void HllDenseGetRegister(uint8_t *val, uint8_t *registers, uint32_t index) {
Review Comment:
```suggestion
uint8_t HllDenseGetRegister(const uint8_t *registers, uint32_t index) {
```
What about changing to this?
##########
src/types/hyperloglog.cc:
##########
@@ -0,0 +1,256 @@
+/*
+ * 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.
+ *
+ */
+
+/* Redis HyperLogLog probabilistic cardinality approximation.
+ * This file implements the algorithm and the exported Redis commands.
+ *
+ * Copyright (c) 2014, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * * Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * * Neither the name of Redis nor the names of its contributors may be used
+ * to endorse or promote products derived from this software without
+ * specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+// NOTE: this file is copy from redis's source: `src/hyperloglog.c`
+
+#include "hyperloglog.h"
+
+#include "murmurhash2.h"
+
+/* Store the value of the register at position 'index' into variable 'val'.
+ * 'registers' is an array of unsigned bytes. */
+void HllDenseGetRegister(uint8_t *val, uint8_t *registers, uint32_t index) {
+ uint32_t byte = index * kHyperLogLogBits / 8;
+ uint8_t fb = index * kHyperLogLogBits & 7;
+ uint8_t fb8 = 8 - fb;
+ uint8_t b0 = registers[byte];
+ uint8_t b1 = registers[byte + 1];
+ *val = ((b0 >> fb) | (b1 << fb8)) & kHyperLogLogRegisterMax;
+}
+
+/* Set the value of the register at position 'index' to 'val'.
+ * 'registers' is an array of unsigned bytes. */
+void HllDenseSetRegister(uint8_t *registers, uint32_t index, uint8_t val) {
+ uint32_t byte = index * kHyperLogLogBits / 8;
+ uint8_t fb = index * kHyperLogLogBits & 7;
+ uint8_t fb8 = 8 - fb;
+ uint8_t v = val;
+ registers[byte] &= ~(kHyperLogLogRegisterMax << fb);
+ registers[byte] |= v << fb;
+ registers[byte + 1] &= ~(kHyperLogLogRegisterMax >> fb8);
+ registers[byte + 1] |= v >> fb8;
+}
+
+/* ========================= HyperLogLog algorithm =========================
*/
+
+/* Given a string element to add to the HyperLogLog, returns the length
+ * of the pattern 000..1 of the element hash. As a side effect
'register_index' is
+ * set which the element hashes to. */
+uint8_t HllPatLen(const std::vector<uint8_t> &element, uint32_t
*register_index) {
+ int elesize = static_cast<int>(element.size());
+ uint64_t hash = 0, bit = 0, index = 0;
+ int count = 0;
+
+ /* Count the number of zeroes starting from bit kHyperLogLogRegisterCount
+ * (that is a power of two corresponding to the first bit we don't use
+ * as index). The max run can be 64-kHyperLogLogRegisterCountPow+1 =
kHyperLogLogHashBitCount+1 bits.
+ *
+ * Note that the final "1" ending the sequence of zeroes must be
+ * included in the count, so if we find "001" the count is 3, and
+ * the smallest count possible is no zeroes at all, just a 1 bit
+ * at the first position, that is a count of 1.
+ *
+ * This may sound like inefficient, but actually in the average case
+ * there are high probabilities to find a 1 after a few iterations. */
+ hash = MurmurHash64A(element.data(), elesize, 0xadc83b19ULL);
Review Comment:
Nit: we can extract this hash to a constant rather than hard code a magic
number?
##########
src/types/hyperloglog.cc:
##########
@@ -0,0 +1,256 @@
+/*
+ * 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.
+ *
+ */
+
+/* Redis HyperLogLog probabilistic cardinality approximation.
+ * This file implements the algorithm and the exported Redis commands.
+ *
+ * Copyright (c) 2014, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * * Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * * Neither the name of Redis nor the names of its contributors may be used
+ * to endorse or promote products derived from this software without
+ * specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+// NOTE: this file is copy from redis's source: `src/hyperloglog.c`
+
+#include "hyperloglog.h"
+
+#include "murmurhash2.h"
+
+/* Store the value of the register at position 'index' into variable 'val'.
+ * 'registers' is an array of unsigned bytes. */
+void HllDenseGetRegister(uint8_t *val, uint8_t *registers, uint32_t index) {
+ uint32_t byte = index * kHyperLogLogBits / 8;
+ uint8_t fb = index * kHyperLogLogBits & 7;
+ uint8_t fb8 = 8 - fb;
+ uint8_t b0 = registers[byte];
+ uint8_t b1 = registers[byte + 1];
+ *val = ((b0 >> fb) | (b1 << fb8)) & kHyperLogLogRegisterMax;
+}
+
+/* Set the value of the register at position 'index' to 'val'.
+ * 'registers' is an array of unsigned bytes. */
+void HllDenseSetRegister(uint8_t *registers, uint32_t index, uint8_t val) {
+ uint32_t byte = index * kHyperLogLogBits / 8;
+ uint8_t fb = index * kHyperLogLogBits & 7;
+ uint8_t fb8 = 8 - fb;
+ uint8_t v = val;
+ registers[byte] &= ~(kHyperLogLogRegisterMax << fb);
+ registers[byte] |= v << fb;
+ registers[byte + 1] &= ~(kHyperLogLogRegisterMax >> fb8);
+ registers[byte + 1] |= v >> fb8;
+}
+
+/* ========================= HyperLogLog algorithm =========================
*/
+
+/* Given a string element to add to the HyperLogLog, returns the length
+ * of the pattern 000..1 of the element hash. As a side effect
'register_index' is
+ * set which the element hashes to. */
+uint8_t HllPatLen(const std::vector<uint8_t> &element, uint32_t
*register_index) {
+ int elesize = static_cast<int>(element.size());
+ uint64_t hash = 0, bit = 0, index = 0;
+ int count = 0;
+
+ /* Count the number of zeroes starting from bit kHyperLogLogRegisterCount
+ * (that is a power of two corresponding to the first bit we don't use
+ * as index). The max run can be 64-kHyperLogLogRegisterCountPow+1 =
kHyperLogLogHashBitCount+1 bits.
+ *
+ * Note that the final "1" ending the sequence of zeroes must be
+ * included in the count, so if we find "001" the count is 3, and
+ * the smallest count possible is no zeroes at all, just a 1 bit
+ * at the first position, that is a count of 1.
+ *
+ * This may sound like inefficient, but actually in the average case
+ * there are high probabilities to find a 1 after a few iterations. */
+ hash = MurmurHash64A(element.data(), elesize, 0xadc83b19ULL);
+ index = hash & kHyperLogLogRegisterCountMask; /* Register index. */
+ hash >>= kHyperLogLogRegisterCountPow; /* Remove bits used to
address the register. */
+ hash |= ((uint64_t)1 << kHyperLogLogHashBitCount); /* Make sure the loop
terminates
+ and count will be <=
kHyperLogLogHashBitCount+1. */
+ bit = 1;
+ count = 1; /* Initialized to 1 since we count the "00000...1" pattern. */
+ while ((hash & bit) == 0) {
+ count++;
+ bit <<= 1;
+ }
+ *register_index = (int)index;
+ return count;
+}
+
+/* Compute the register histogram in the dense representation. */
+void HllDenseRegHisto(uint8_t *registers, int *reghisto) {
+ /* Redis default is to use 16384 registers 6 bits each. The code works
+ * with other values by modifying the defines, but for our target value
+ * we take a faster path with unrolled loops. */
+ if (kHyperLogLogRegisterCount == 16384 && kHyperLogLogBits == 6) {
Review Comment:
Can we remove `if` since else would never happens?
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