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/*
* include/shard/FSTrie.h
*
* Copyright (C) 2024 Douglas B. Rumbaugh <drumbaugh@psu.edu>
*
* Distributed under the Modified BSD License.
*
* A shard shim around the FSTrie learned index.
*/
#pragma once
#include <vector>
#include "framework/ShardRequirements.h"
#include "fst.hpp"
#include "util/SortedMerge.h"
using psudb::CACHELINE_SIZE;
using psudb::BloomFilter;
using psudb::PriorityQueue;
using psudb::queue_record;
using psudb::byte;
namespace de {
template <KVPInterface R>
class FSTrie {
public:
typedef R RECORD;
private:
typedef decltype(R::key) K;
typedef decltype(R::value) V;
static_assert(std::is_same_v<K, const char*>, "FST requires const char* keys.");
public:
FSTrie(BufferView<R> buffer)
: m_data(nullptr)
, m_reccnt(0)
, m_alloc_size(0)
{
m_data = new Wrapped<R>[buffer.get_record_count()]();
m_alloc_size = sizeof(Wrapped<R>) * buffer.get_record_count();
size_t cnt = 0;
std::vector<std::string> keys;
keys.reserve(buffer.get_record_count());
/*
* Copy the contents of the buffer view into a temporary buffer, and
* sort them. We still need to iterate over these temporary records to
* apply tombstone/deleted record filtering, as well as any possible
* per-record processing that is required by the shard being built.
*/
auto temp_buffer = new Wrapped<R>[buffer.get_record_count()]();
for (size_t i=0; i<buffer.get_record_count(); i++) {
temp_buffer[i] = *(buffer.get(i));
}
auto base = temp_buffer;
auto stop = base + buffer.get_record_count();
std::sort(base, stop, std::less<Wrapped<R>>());
for (size_t i=0; i<buffer.get_record_count(); i++) {
if (temp_buffer[i].is_deleted() || !temp_buffer[i].is_visible() || temp_buffer[i].rec.key == "") {
continue;
}
m_data[cnt] = temp_buffer[i];
m_data[cnt].clear_timestamp();
keys.push_back(std::string(m_data[cnt].rec.key));
cnt++;
}
m_reccnt = cnt;
if (m_reccnt > 0) {
m_fst = new fst::Trie(keys, true, 1);
}
delete[] temp_buffer;
}
FSTrie(std::vector<const FSTrie*> const &shards)
: m_data(nullptr)
, m_reccnt(0)
, m_alloc_size(0)
{
size_t attemp_reccnt = 0;
size_t tombstone_count = 0;
auto cursors = build_cursor_vec<R, FSTrie>(shards, &attemp_reccnt, &tombstone_count);
m_data = new Wrapped<R>[attemp_reccnt]();
m_alloc_size = attemp_reccnt * sizeof(Wrapped<R>);
std::vector<std::string> keys;
keys.reserve(attemp_reccnt);
// FIXME: For smaller cursor arrays, it may be more efficient to skip
// the priority queue and just do a scan.
PriorityQueue<Wrapped<R>> pq(cursors.size());
for (size_t i=0; i<cursors.size(); i++) {
pq.push(cursors[i].ptr, i);
}
while (pq.size()) {
auto now = pq.peek();
auto next = pq.size() > 1 ? pq.peek(1) : queue_record<Wrapped<R>>{nullptr, 0};
/*
* if the current record is not a tombstone, and the next record is
* a tombstone that matches the current one, then the current one
* has been deleted, and both it and its tombstone can be skipped
* over.
*/
if (!now.data->is_tombstone() && next.data != nullptr &&
now.data->rec == next.data->rec && next.data->is_tombstone()) {
pq.pop(); pq.pop();
auto& cursor1 = cursors[now.version];
auto& cursor2 = cursors[next.version];
if (advance_cursor(cursor1)) pq.push(cursor1.ptr, now.version);
if (advance_cursor(cursor2)) pq.push(cursor2.ptr, next.version);
} else {
auto& cursor = cursors[now.version];
/* skip over records that have been deleted via tagging */
if (!cursor.ptr->is_deleted() && cursor.ptr->rec.key != "") {
m_data[m_reccnt] = *cursor.ptr;
keys.push_back(std::string(m_data[m_reccnt].rec.key));
m_reccnt++;
}
pq.pop();
if (advance_cursor(cursor)) pq.push(cursor.ptr, now.version);
}
}
if (m_reccnt > 0) {
m_fst = new fst::Trie(keys, true, 1);
}
}
~FSTrie() {
delete[] m_data;
delete m_fst;
}
Wrapped<R> *point_lookup(const R &rec, bool filter=false) {
auto idx = m_fst->exactSearch(rec.key);
if (idx == fst::kNotFound) {
return nullptr;
}
// FIXME: for convenience, I'm treating this Trie as a unique index
// for now, so no need to scan forward and/or check values. This
// also makes the point lookup query class a lot easier to make.
// Ultimately, though, we can support non-unique indexes with some
// extra work.
return m_data + idx;
}
Wrapped<R>* get_data() const {
return m_data;
}
size_t get_record_count() const {
return m_reccnt;
}
size_t get_tombstone_count() const {
return 0;
}
const Wrapped<R>* get_record_at(size_t idx) const {
if (idx >= m_reccnt) return nullptr;
return m_data + idx;
}
size_t get_memory_usage() const {
return m_fst->getMemoryUsage();
}
size_t get_aux_memory_usage() const {
return m_alloc_size;
}
size_t get_lower_bound(R &rec) {return 0;}
size_t get_upper_bound(R &rec) {return 0;}
private:
Wrapped<R>* m_data;
size_t m_reccnt;
size_t m_alloc_size;
fst::Trie *m_fst;
};
}
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