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Implement an option to have parallel index load #524

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Implement an option to have parallel index load #524

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48 changes: 45 additions & 3 deletions hnswlib/hnswalg.h
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
#include <assert.h>
#include <unordered_set>
#include <list>
#include <thread>

namespace hnswlib {
typedef unsigned int tableint;
Expand Down Expand Up @@ -77,11 +78,12 @@ class HierarchicalNSW : public AlgorithmInterface<dist_t> {
HierarchicalNSW(
SpaceInterface<dist_t> *s,
const std::string &location,
bool parallel_load = false,
bool nmslib = false,
size_t max_elements = 0,
bool allow_replace_deleted = false)
: allow_replace_deleted_(allow_replace_deleted) {
loadIndex(location, s, max_elements);
loadIndex(location, s, max_elements, parallel_load);
}


Expand Down Expand Up @@ -627,7 +629,7 @@ class HierarchicalNSW : public AlgorithmInterface<dist_t> {
}


void loadIndex(const std::string &location, SpaceInterface<dist_t> *s, size_t max_elements_i = 0) {
void loadIndex(const std::string &location, SpaceInterface<dist_t> *s, size_t max_elements_i = 0, bool parallel_load = false) {
std::ifstream input(location, std::ios::binary);

if (!input.is_open())
Expand Down Expand Up @@ -690,7 +692,14 @@ class HierarchicalNSW : public AlgorithmInterface<dist_t> {
data_level0_memory_ = (char *) malloc(max_elements * size_data_per_element_);
if (data_level0_memory_ == nullptr)
throw std::runtime_error("Not enough memory: loadIndex failed to allocate level0");
input.read(data_level0_memory_, cur_element_count * size_data_per_element_);

size_t level0_size = cur_element_count * size_data_per_element_;
if (parallel_load) {
parallelLoadLevel0(location, pos);
input.seekg(pos + level0_size);
} else {
input.read(data_level0_memory_, level0_size);
}

size_links_per_element_ = maxM_ * sizeof(tableint) + sizeof(linklistsizeint);

Expand Down Expand Up @@ -1267,5 +1276,38 @@ class HierarchicalNSW : public AlgorithmInterface<dist_t> {
}
std::cout << "integrity ok, checked " << connections_checked << " connections\n";
}

protected:


void loadLevel0Chunk(const std::string &location, const size_t level0_start_pos, size_t offset, size_t size) {
std::ifstream in_file(location, std::ios::binary);

if (!in_file.is_open())
throw std::runtime_error("Cannot open file");

in_file.seekg(level0_start_pos + offset);
in_file.read(data_level0_memory_ + offset, size);
in_file.close();
}


void parallelLoadLevel0(const std::string &location, std::streampos level0_start_pos) {
size_t level0_size = cur_element_count * size_data_per_element_;
size_t num_cpu_threads = std::thread::hardware_concurrency();
size_t part_sz = level0_size / num_cpu_threads;

std::vector<std::thread> threads;
size_t offset = 0;
for (size_t i = 0; i < num_cpu_threads - 1; i++) {
threads.emplace_back(&HierarchicalNSW<dist_t>::loadLevel0Chunk, this, location, level0_start_pos, offset, part_sz);
offset += part_sz;
}

loadLevel0Chunk(location, level0_start_pos, offset, part_sz + level0_size % num_cpu_threads);

for (auto& thread : threads)
thread.join();
}
};
} // namespace hnswlib