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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 <WeightedRecordInterface R>
struct Parms {
size_t sample_size;
gsl_rng *rng;
};
template <WeightedRecordInterface R>
struct State {
decltype(R::weight) total_weight;
size_t sample_size;
State() {
total_weight = 0;
}
};
template <RecordInterface R>
struct BufferState {
size_t cutoff;
size_t sample_size;
psudb::Alias *alias;
decltype(R::weight) max_weight;
decltype(R::weight) total_weight;
BufferView<R> *buffer;
~BufferState() {
delete alias;
}
};
template <RecordInterface R, ShardInterface<R> S, bool Rejection=true>
class Query {
public:
constexpr static bool EARLY_ABORT=false;
constexpr static bool SKIP_DELETE_FILTER=false;
static void *get_query_state(S *shard, void *parms) {
auto res = new State<R>();
res->total_weight = shard->get_total_weight();
res->sample_size = 0;
return res;
}
static void* get_buffer_query_state(BufferView<R> *buffer, void *parms) {
BufferState<R> *state = new BufferState<R>();
auto parameters = (Parms<R>*) parms;
if constexpr (Rejection) {
state->cutoff = buffer->get_record_count() - 1;
state->max_weight = buffer->get_max_weight();
state->total_weight = buffer->get_total_weight();
state->buffer = buffer;
return state;
}
std::vector<double> weights;
double total_weight = 0.0;
state->buffer = buffer;
for (size_t i = 0; i <= buffer->get_record_count(); i++) {
auto rec = buffer->get_data(i);
weights.push_back(rec->rec.weight);
total_weight += rec->rec.weight;
}
for (size_t i = 0; i < weights.size(); i++) {
weights[i] = weights[i] / total_weight;
}
state->alias = new psudb::Alias(weights);
state->total_weight = total_weight;
return state;
}
static void process_query_states(void *query_parms, std::vector<void*> &shard_states, std::vector<void*> &buffer_states) {
auto p = (Parms<R> *) query_parms;
std::vector<size_t> shard_sample_sizes(shard_states.size()+buffer_states.size(), 0);
size_t buffer_sz = 0;
std::vector<decltype(R::weight)> weights;
decltype(R::weight) total_weight = 0;
for (auto &s : buffer_states) {
auto bs = (BufferState<R> *) s;
total_weight += bs->total_weight;
weights.push_back(bs->total_weight);
}
for (auto &s : shard_states) {
auto state = (State<R> *) s;
total_weight += state->total_weight;
weights.push_back(state->total_weight);
}
std::vector<double> normalized_weights;
for (auto w : weights) {
normalized_weights.push_back((double) w / (double) total_weight);
}
auto shard_alias = psudb::Alias(normalized_weights);
for (size_t i=0; i<p->sample_size; i++) {
auto idx = shard_alias.get(p->rng);
if (idx < buffer_states.size()) {
auto state = (BufferState<R> *) buffer_states[idx];
state->sample_size++;
} else {
auto state = (State<R> *) shard_states[idx - buffer_states.size()];
state->sample_size++;
}
}
}
static std::vector<Wrapped<R>> query(S *shard, void *q_state, void *parms) {
auto rng = ((Parms<R> *) parms)->rng;
auto state = (State<R> *) q_state;
auto sample_size = state->sample_size;
std::vector<Wrapped<R>> result_set;
if (sample_size == 0) {
return result_set;
}
size_t attempts = 0;
do {
attempts++;
size_t idx = shard->get_weighted_sample(rng);
result_set.emplace_back(*shard->get_record_at(idx));
} while (attempts < sample_size);
return result_set;
}
static std::vector<Wrapped<R>> buffer_query(void *state, void *parms) {
auto st = (BufferState<R> *) state;
auto p = (Parms<R> *) parms;
auto buffer = st->buffer;
std::vector<Wrapped<R>> result;
result.reserve(st->sample_size);
if constexpr (Rejection) {
for (size_t i=0; i<st->sample_size; i++) {
auto idx = gsl_rng_uniform_int(p->rng, st->cutoff);
auto rec = buffer->get(idx);
auto test = gsl_rng_uniform(p->rng) * st->max_weight;
if (test <= rec->rec.weight) {
result.emplace_back(*rec);
}
}
return result;
}
for (size_t i=0; i<st->sample_size; i++) {
auto idx = st->alias->get(p->rng);
result.emplace_back(*(buffer->get_data() + idx));
}
return result;
}
static std::vector<R> merge(std::vector<std::vector<Wrapped<R>>> &results, void *parms, std::vector<R> &output) {
for (size_t i=0; i<results.size(); i++) {
for (size_t j=0; j<results[i].size(); j++) {
output.emplace_back(results[i][j].rec);
}
}
return output;
}
static void delete_query_state(void *state) {
auto s = (State<R> *) state;
delete s;
}
static void delete_buffer_query_state(void *state) {
auto s = (BufferState<R> *) state;
delete s;
}
static bool repeat(void *parms, std::vector<R> &results, std::vector<void*> states, void* buffer_state) {
auto p = (Parms<R> *) parms;
if (results.size() < p->sample_size) {
return true;
}
return false;
}
};
}}
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