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/*
* include/query/wss.h
*
* Copyright (C) 2023 Douglas B. Rumbaugh <drumbaugh@psu.edu>
*
* Distributed under the Modified BSD License.
*
* A query class for weighted set sampling. This
* class is tightly coupled with include/shard/Alias.h,
* and so is probably of limited general utility.
*/
#pragma once
#include "framework/QueryRequirements.h"
#include "psu-ds/Alias.h"
namespace de {
namespace wss {
template <ShardInterface S> class Query {
typedef typename S::RECORD R;
public:
struct Parameters {
size_t sample_size;
gsl_rng *rng;
};
struct LocalQuery {
size_t sample_size;
decltype(R::weight) total_weight;
Parameters global_parms;
};
struct LocalQueryBuffer {
BufferView<R> *buffer;
size_t sample_size;
decltype(R::weight) total_weight;
decltype(R::weight) max_weight;
size_t cutoff;
std::unique_ptr<psudb::Alias> alias;
Parameters global_parms;
};
constexpr static bool EARLY_ABORT = false;
constexpr static bool SKIP_DELETE_FILTER = false;
typedef Wrapped<R> LocalResultType;
typedef R ResultType;
static LocalQuery *local_preproc(S *shard, Parameters *parms) {
auto query = new LocalQuery();
query->global_parms = *parms;
query->total_weight = shard->get_total_weight();
query->sample_size = 0;
return query;
}
static LocalQueryBuffer *local_preproc_buffer(BufferView<R> *buffer,
Parameters *parms) {
auto query = new LocalQueryBuffer();
query->cutoff = buffer->get_record_count() - 1;
query->max_weight = 0;
query->total_weight = 0;
for (size_t i = 0; i < buffer->get_record_count(); i++) {
auto weight = buffer->get(i)->rec.weight;
query->total_weight += weight;
if (weight > query->max_weight) {
query->max_weight = weight;
}
}
query->buffer = buffer;
query->global_parms = *parms;
query->alias = nullptr;
return query;
}
static void distribute_query(Parameters *parms,
std::vector<LocalQuery *> const &local_queries,
LocalQueryBuffer *buffer_query) {
if (!buffer_query) {
assert(local_queries.size() == 1);
local_queries[0]->sample_size =
local_queries[0]->global_parms.sample_size;
return;
}
if (!buffer_query->alias) {
std::vector<decltype(R::weight)> weights;
decltype(R::weight) total_weight = buffer_query->total_weight;
weights.push_back(total_weight);
for (auto &q : local_queries) {
total_weight += q->total_weight;
weights.push_back(q->total_weight);
q->sample_size = 0;
}
std::vector<double> normalized_weights;
for (auto w : weights) {
normalized_weights.push_back((double)w / (double)total_weight);
}
buffer_query->alias = std::make_unique<psudb::Alias>(normalized_weights);
}
for (size_t i = 0; i < parms->sample_size; i++) {
auto idx = buffer_query->alias->get(parms->rng);
if (idx == 0) {
buffer_query->sample_size++;
} else {
local_queries[idx - 1]->sample_size++;
}
}
}
static std::vector<LocalResultType> local_query(S *shard, LocalQuery *query) {
std::vector<LocalResultType> result;
if (query->sample_size == 0) {
return result;
}
for (size_t i = 0; i < query->sample_size; i++) {
size_t idx = shard->get_weighted_sample(query->global_parms.rng);
if (!shard->get_record_at(idx)->is_deleted()) {
result.emplace_back(*shard->get_record_at(idx));
}
}
return result;
}
static std::vector<LocalResultType>
local_query_buffer(LocalQueryBuffer *query) {
std::vector<LocalResultType> result;
for (size_t i = 0; i < query->sample_size; i++) {
auto idx = gsl_rng_uniform_int(query->global_parms.rng, query->cutoff);
auto rec = query->buffer->get(idx);
auto test = gsl_rng_uniform(query->global_parms.rng) * query->max_weight;
if (test <= rec->rec.weight && !rec->is_deleted()) {
result.emplace_back(*rec);
}
}
return result;
}
static void
combine(std::vector<std::vector<LocalResultType>> const &local_results,
Parameters *parms, std::vector<ResultType> &output) {
for (size_t i = 0; i < local_results.size(); i++) {
for (size_t j = 0; j < local_results[i].size(); j++) {
output.emplace_back(local_results[i][j].rec);
}
}
}
static bool repeat(Parameters *parms, std::vector<ResultType> &output,
std::vector<LocalQuery *> const &local_queries,
LocalQueryBuffer *buffer_query) {
if (output.size() < parms->sample_size) {
parms->sample_size -= output.size();
distribute_query(parms, local_queries, buffer_query);
return true;
}
return false;
}
};
} // namespace wss
} // namespace de
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