1 files changed, 207 insertions, 0 deletions
diff --git a/include/shard/Alias.h b/include/shard/Alias.h
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+++ b/include/shard/Alias.h
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+/*
+ * include/shard/Alias.h
+ *
+ * Copyright (C) 2023 Douglas B. Rumbaugh <drumbaugh@psu.edu>
+ *                    Dong Xie <dongx@psu.edu>
+ *
+ * Distributed under the Modified BSD License.
+ *
+ * A shard shim around the psudb::Alias Walker's Alias
+ * structure. Designed to be used along side the WSS
+ * query in include/query/wss.h
+ *
+ * TODO: The code in this file is very poorly commented.
+ */
+#pragma once
+
+#include <vector>
+
+#include "framework/ShardRequirements.h"
+
+#include "psu-ds/Alias.h"
+#include "psu-ds/BloomFilter.h"
+#include "util/bf_config.h"
+#include "util/SortedMerge.h"
+
+using psudb::CACHELINE_SIZE;
+using psudb::BloomFilter;
+using psudb::PriorityQueue;
+using psudb::queue_record;
+using psudb::byte;
+
+namespace de {
+
+static thread_local size_t wss_cancelations = 0;
+
+template <WeightedRecordInterface R>
+class Alias {
+private:
+    typedef decltype(R::key) K;
+    typedef decltype(R::value) V;
+    typedef decltype(R::weight) W;
+
+public:
+    Alias(BufferView<R> buffer)
+        : m_data(nullptr)
+        , m_alias(nullptr)
+        , m_total_weight(0)
+        , m_reccnt(0)
+        , m_tombstone_cnt(0)
+        , m_alloc_size(0)
+        , m_bf(new BloomFilter<R>(BF_FPR, buffer.get_tombstone_count(), BF_HASH_FUNCS)) {
+                       
+
+        m_alloc_size = psudb::sf_aligned_alloc(CACHELINE_SIZE, 
+                                               buffer.get_record_count() * 
+                                                 sizeof(Wrapped<R>), 
+                                               (byte**) &m_data);
+
+        auto res = sorted_array_from_bufferview<R>(std::move(buffer), m_data, m_bf);
+        m_reccnt = res.record_count;
+        m_tombstone_cnt = res.tombstone_count;
+
+        if (m_reccnt > 0) {
+            std::vector<W> weights;
+            for (size_t i=0; i<m_reccnt; i++) {
+                weights.emplace_back(m_data[i].rec.weight);
+                m_total_weight += m_data[i].rec.weight;
+            }
+
+            build_alias_structure(weights);
+        }
+    }
+
+    Alias(std::vector<Alias*> &shards)
+        : m_data(nullptr)
+        , m_alias(nullptr)
+        , m_total_weight(0)
+        , m_reccnt(0)
+        , m_tombstone_cnt(0)
+        , m_alloc_size(0)
+        , m_bf(nullptr) {
+
+        size_t attemp_reccnt = 0;
+        size_t tombstone_count = 0;
+        auto cursors = build_cursor_vec<R, Alias>(shards, &attemp_reccnt, &tombstone_count);
+
+        m_bf = new BloomFilter<R>(BF_FPR, tombstone_count, BF_HASH_FUNCS);
+        m_alloc_size = psudb::sf_aligned_alloc(CACHELINE_SIZE, 
+                                               attemp_reccnt * sizeof(Wrapped<R>),
+                                               (byte **) &m_data);
+
+        auto res = sorted_array_merge<R>(cursors, m_data, m_bf);
+        m_reccnt = res.record_count;
+        m_tombstone_cnt = res.tombstone_count;
+
+        if (m_reccnt > 0) {
+            std::vector<W> weights;
+            for (size_t i=0; i<m_reccnt; i++) {
+                weights.emplace_back(m_data[i].rec.weight);
+                m_total_weight += m_data[i].rec.weight;
+            }
+
+            build_alias_structure(weights);
+        }
+   }
+
+    ~Alias() {
+        free(m_data);
+        delete m_alias;
+        delete m_bf;
+    }
+
+    Wrapped<R> *point_lookup(const R &rec, bool filter=false) {
+        if (filter && !m_bf->lookup(rec)) {
+            return nullptr;
+        }
+
+        size_t idx = get_lower_bound(rec.key);
+        if (idx >= m_reccnt) {
+            return nullptr;
+        }
+
+        while (idx < (m_reccnt-1) && m_data[idx].rec < rec) ++idx;
+
+        if (m_data[idx].rec == rec) {
+            return m_data + idx;
+        }
+
+        return nullptr;
+    }
+
+    Wrapped<R>* get_data() const {
+        return m_data;
+    }
+    
+    size_t get_record_count() const {
+        return m_reccnt;
+    }
+
+    size_t get_tombstone_count() const {
+        return m_tombstone_cnt;
+    }
+
+    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() {
+        return m_alloc_size;
+    }
+
+    size_t get_aux_memory_usage() {
+        return (m_bf) ? m_bf->memory_usage() : 0;
+    }
+
+    W get_total_weight() {
+        return m_total_weight;
+    }
+
+    size_t get_weighted_sample(gsl_rng *rng) const {
+        return m_alias->get(rng);
+    }
+
+    size_t get_lower_bound(const K& key) const {
+        size_t min = 0;
+        size_t max = m_reccnt - 1;
+
+        const char * record_key;
+        while (min < max) {
+            size_t mid = (min + max) / 2;
+
+            if (key > m_data[mid].rec.key) {
+                min = mid + 1;
+            } else {
+                max = mid;
+            }
+        }
+
+        return min;
+    }
+
+private:
+
+    void build_alias_structure(std::vector<W> &weights) {
+
+        // normalize the weights vector
+        std::vector<double> norm_weights(weights.size());
+
+        for (size_t i=0; i<weights.size(); i++) {
+            norm_weights[i] = (double) weights[i] / (double) m_total_weight;
+        }
+
+        // build the alias structure
+        m_alias = new psudb::Alias(norm_weights);
+    }
+
+    Wrapped<R>* m_data;
+    psudb::Alias *m_alias;
+    W m_total_weight;
+    size_t m_reccnt;
+    size_t m_tombstone_cnt;
+    size_t m_alloc_size;
+    BloomFilter<R> *m_bf;
+};
+}