1 files changed, 200 insertions, 0 deletions
diff --git a/include/shard/FSTrie.h b/include/shard/FSTrie.h
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+++ b/include/shard/FSTrie.h
@@ -0,0 +1,200 @@
+/*
+ * 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 {
+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<FSTrie*> &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() {
+        return m_fst->getMemoryUsage();
+    }
+
+    size_t get_aux_memory_usage() {
+        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;
+};
+}