Merge pull request #1 from dbrumbaugh/new-buffer

Initial Concurrency Implementation

1 files changed, 205 insertions, 0 deletions

diff --git a/include/util/SortedMerge.h b/include/util/SortedMerge.h
new file mode 100644
index 0000000..8a1e782
--- /dev/null
+++ b/include/util/SortedMerge.h
@@ -0,0 +1,205 @@
+/*
+ * include/util/SortedMerge.h
+ *
+ * Copyright (C) 2023 Douglas B. Rumbaugh <drumbaugh@psu.edu> 
+ *
+ * Distributed under the Modified BSD License.
+ *
+ * A sorted array merge routine for use in Shard construction, as many
+ * shards will use a sorted array to represent their data. Also encapsulates 
+ * the necessary tombstone-cancellation logic.
+ *
+ * FIXME: include generic per-record processing functionality for Shards that 
+ * need it, to avoid needing to reprocess the array in the shard after
+ * creation.
+ */
+#pragma once
+
+#include "util/Cursor.h"
+#include "framework/interface/Shard.h"
+#include "psu-ds/PriorityQueue.h"
+
+namespace de {
+
+using psudb::PriorityQueue;
+using psudb::BloomFilter;
+using psudb::queue_record;
+using psudb::byte;
+using psudb::CACHELINE_SIZE;
+
+/*
+ * A simple struct to return record_count and tombstone_count information 
+ * back to the caller. Could've been an std::pair, but I like the more 
+ * explicit names.
+ */
+struct merge_info {
+    size_t record_count;
+    size_t tombstone_count;
+};
+
+/*
+ * Build a vector of cursors corresponding to the records contained within
+ * a vector of shards. The cursor at index i in the output will correspond
+ * to the shard at index i in the input. 
+ *
+ * The values of reccnt and tscnt will be updated with the sum of the
+ * records contained within the shards. Note that these counts include deleted
+ * records that may be removed during shard construction, and so constitute
+ * upper bounds only.
+ */
+template <RecordInterface R, ShardInterface<R> S>
+static std::vector<Cursor<Wrapped<R>>> build_cursor_vec(std::vector<S*> &shards, size_t *reccnt, size_t *tscnt) {
+    std::vector<Cursor<Wrapped<R>>> cursors;
+    cursors.reserve(shards.size());
+
+    *reccnt = 0;
+    *tscnt = 0;
+    
+    for (size_t i = 0; i < shards.size(); ++i) {
+        if (shards[i]) {
+            auto base = shards[i]->get_data();
+            cursors.emplace_back(Cursor{base, base + shards[i]->get_record_count(), 0, shards[i]->get_record_count()});
+            *reccnt += shards[i]->get_record_count();
+            *tscnt += shards[i]->get_tombstone_count();
+        } else {
+            cursors.emplace_back(Cursor<Wrapped<R>>{nullptr, nullptr, 0, 0});
+        }
+    }
+
+    return cursors;
+}
+
+/*
+ * Build a sorted array of records based on the contents of a BufferView.
+ * This routine does not alter the buffer view, but rather copies the
+ * records out and then sorts them. The provided buffer must be large
+ * enough to store the records from the BufferView, or the behavior of the
+ * function is undefined.
+ *
+ * It allocates a temporary buffer for the sorting, and execution of the
+ * program will be aborted if the allocation fails.
+ */
+template <RecordInterface R>
+static merge_info sorted_array_from_bufferview(BufferView<R> bv, 
+                                               Wrapped<R> *buffer,
+                                               psudb::BloomFilter<R> *bf=nullptr) {
+    /*
+     * 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 = (Wrapped<R> *) psudb::sf_aligned_calloc(CACHELINE_SIZE, 
+                                                               bv.get_record_count(), 
+                                                               sizeof(Wrapped<R>));
+    bv.copy_to_buffer((byte *) temp_buffer);
+
+    auto base = temp_buffer;
+    auto stop = base + bv.get_record_count();
+    std::sort(base, stop, std::less<Wrapped<R>>());
+
+    merge_info info = {0, 0};
+
+    /* 
+     * Iterate over the temporary buffer to process the records, copying
+     * them into buffer as needed
+     */
+    while (base < stop) {
+        if (!base->is_tombstone() && (base + 1 < stop)
+            && base->rec == (base + 1)->rec  && (base + 1)->is_tombstone()) {
+            base += 2;
+            continue;
+        } else if (base->is_deleted()) {
+            base += 1;
+            continue;
+        }
+
+        // FIXME: this shouldn't be necessary, but the tagged record
+        // bypass doesn't seem to be working on this code-path, so this
+        // ensures that tagged records from the buffer are able to be
+        // dropped, eventually. It should only need to be &= 1
+        base->header &= 3;
+        buffer[info.record_count++] = *base;
+
+        if (base->is_tombstone()) {
+            info.tombstone_count++;
+            if (bf){
+                bf->insert(base->rec);
+            }
+        }
+
+        base++;
+    }
+
+    free(temp_buffer);
+    return info;
+}
+
+/*
+ * Perform a sorted merge of the records within cursors into the provided
+ * buffer. Includes tombstone and tagged delete cancellation logic, and
+ * will insert tombstones into a bloom filter, if one is provided. 
+ *
+ * The behavior of this function is undefined if the provided buffer does
+ * not have space to contain all of the records within the input cursors.
+ */
+template <RecordInterface R>
+static merge_info sorted_array_merge(std::vector<Cursor<Wrapped<R>>> &cursors, 
+                              Wrapped<R> *buffer, 
+                              psudb::BloomFilter<R> *bf=nullptr) {
+    
+    // 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);
+    }
+
+    merge_info info = {0, 0};
+    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()) {
+                buffer[info.record_count++] = *cursor.ptr;
+
+                /*  
+                 * if the record is a tombstone, increment the ts count and 
+                 * insert it into the bloom filter if one has been
+                 * provided.
+                 */
+                if (cursor.ptr->is_tombstone()) {
+                    info.tombstone_count++;
+                    if (bf) {
+                        bf->insert(cursor.ptr->rec);
+                    }
+                }
+            }
+            pq.pop();
+            
+            if (advance_cursor(cursor)) pq.push(cursor.ptr, now.version);
+        }
+    }
+
+    return info;
+}
+
+
+
+}