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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include "hnsw_index_traits.h"
#include "hnsw_simple_node.h"
#include "hnsw_node.h"
#include <vespa/vespalib/datastore/array_store.h>
#include <vespa/vespalib/datastore/atomic_entry_ref.h>
#include <vespa/vespalib/datastore/entryref.h>
#include <vespa/vespalib/util/rcuvector.h>
namespace search::tensor {
/**
* Storage of a hierarchical navigable small world graph (HNSW)
* that is used for approximate K-nearest neighbor search.
*/
template <HnswIndexType type>
struct HnswGraph {
using AtomicEntryRef = vespalib::datastore::AtomicEntryRef;
// This uses 10 bits for buffer id -> 1024 buffers.
// As we have very short arrays we get less fragmentation with fewer and larger buffers.
using LevelArrayEntryRefType = vespalib::datastore::EntryRefT<22>;
// This uses 12 bits for buffer id -> 4096 buffers.
using LinkArrayEntryRefType = vespalib::datastore::EntryRefT<20>;
static constexpr HnswIndexType index_type = type;
using NodeType = typename HnswIndexTraits<type>::NodeType;
// Provides mapping from document id -> node reference.
// The reference is used to lookup the node data in LevelArrayStore.
using NodeVector = vespalib::RcuVector<NodeType>;
using LevelsRef = vespalib::datastore::EntryRef;
// This stores the level arrays for all nodes.
// Each node consists of an array of levels (from level 0 to n) where each entry is a reference to the link array at that level.
using LevelArrayStore = vespalib::datastore::ArrayStore<AtomicEntryRef, LevelArrayEntryRefType>;
using LevelArrayRef = LevelArrayStore::ConstArrayRef;
// This stores all link arrays.
// A link array consists of the document ids of the nodes a particular node is linked to.
using LinkArrayStore = vespalib::datastore::ArrayStore<uint32_t, LinkArrayEntryRefType>;
using LinkArrayRef = LinkArrayStore::ConstArrayRef;
NodeVector nodes;
std::atomic<uint32_t> nodes_size;
LevelArrayStore levels_store;
LinkArrayStore links_store;
std::atomic<uint64_t> entry_nodeid_and_level;
HnswGraph();
~HnswGraph();
LevelsRef make_node(uint32_t nodeid, uint32_t docid, uint32_t subspace, uint32_t num_levels);
void remove_node(uint32_t nodeid);
void trim_nodes_size();
LevelsRef get_levels_ref(uint32_t nodeid) const {
return nodes.get_elem_ref(nodeid).levels_ref().load_relaxed(); // Called from writer only
}
const NodeType& acquire_node(uint32_t nodeid) const {
return nodes.acquire_elem_ref(nodeid);
}
LevelsRef acquire_levels_ref(uint32_t nodeid) const {
return nodes.acquire_elem_ref(nodeid).levels_ref().load_acquire();
}
bool still_valid(uint32_t nodeid, LevelsRef levels_ref) const {
return levels_ref.valid() && (acquire_levels_ref(nodeid) == levels_ref);
}
LevelArrayRef get_level_array(LevelsRef levels_ref) const {
if (levels_ref.valid()) {
return levels_store.get(levels_ref);
}
return LevelArrayRef();
}
LevelArrayRef get_level_array(uint32_t nodeid) const {
auto levels_ref = get_levels_ref(nodeid);
return get_level_array(levels_ref);
}
LevelArrayRef acquire_level_array(uint32_t nodeid) const {
auto levels_ref = acquire_levels_ref(nodeid);
return get_level_array(levels_ref);
}
LinkArrayRef get_link_array(LevelArrayRef levels, uint32_t level) const {
if (level < levels.size()) {
auto links_ref = levels[level].load_acquire();
if (links_ref.valid()) {
return links_store.get(links_ref);
}
}
return LinkArrayRef();
}
LinkArrayRef get_link_array(uint32_t nodeid, uint32_t level) const {
auto levels = get_level_array(nodeid);
return get_link_array(levels, level);
}
LinkArrayRef acquire_link_array(uint32_t nodeid, uint32_t level) const {
auto levels = acquire_level_array(nodeid);
return get_link_array(levels, level);
}
LinkArrayRef get_link_array(LevelsRef levels_ref, uint32_t level) const {
auto levels = get_level_array(levels_ref);
return get_link_array(levels, level);
}
void set_link_array(uint32_t nodeid, uint32_t level, const LinkArrayRef& new_links);
struct EntryNode {
uint32_t nodeid;
LevelsRef levels_ref;
int32_t level;
EntryNode()
: nodeid(0), // Note that nodeid 0 is reserved and never used
levels_ref(),
level(-1)
{}
EntryNode(uint32_t nodeid_in, LevelsRef levels_ref_in, int32_t level_in)
: nodeid(nodeid_in),
levels_ref(levels_ref_in),
level(level_in)
{}
};
void set_entry_node(EntryNode node);
uint64_t get_entry_atomic() const {
return entry_nodeid_and_level.load(std::memory_order_acquire);
}
EntryNode get_entry_node() const {
EntryNode entry;
while (true) {
uint64_t value = get_entry_atomic();
entry.nodeid = (uint32_t)value;
entry.levels_ref = acquire_levels_ref(entry.nodeid);
entry.level = (int32_t)(value >> 32);
if ((entry.nodeid == 0)
&& (entry.level == -1)
&& ! entry.levels_ref.valid())
{
// invalid in every way
return entry;
}
if ((entry.nodeid > 0)
&& (entry.level > -1)
&& entry.levels_ref.valid()
&& (get_entry_atomic() == value))
{
// valid in every way
return entry;
}
}
}
size_t size() const { return nodes_size.load(std::memory_order_acquire); }
struct Histograms {
std::vector<uint32_t> level_histogram;
std::vector<uint32_t> links_histogram;
};
Histograms histograms() const;
};
}
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