290 lines
8.9 KiB
C++
290 lines
8.9 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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#include "memtable/inlineskiplist.h"
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#include "db/memtable.h"
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#include "rocksdb/memtablerep.h"
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#include "util/arena.h"
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namespace rocksdb {
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namespace {
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class SkipListRep : public MemTableRep {
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InlineSkipList<const MemTableRep::KeyComparator&> skip_list_;
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const MemTableRep::KeyComparator& cmp_;
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const SliceTransform* transform_;
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const size_t lookahead_;
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friend class LookaheadIterator;
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public:
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explicit SkipListRep(const MemTableRep::KeyComparator& compare,
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Allocator* allocator, const SliceTransform* transform,
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const size_t lookahead)
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: MemTableRep(allocator),
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skip_list_(compare, allocator),
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cmp_(compare),
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transform_(transform),
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lookahead_(lookahead) {}
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virtual KeyHandle Allocate(const size_t len, char** buf) override {
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*buf = skip_list_.AllocateKey(len);
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return static_cast<KeyHandle>(*buf);
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}
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// Insert key into the list.
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// REQUIRES: nothing that compares equal to key is currently in the list.
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virtual void Insert(KeyHandle handle) override {
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skip_list_.Insert(static_cast<char*>(handle));
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}
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virtual bool InsertKey(KeyHandle handle) override {
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return skip_list_.Insert(static_cast<char*>(handle));
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}
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virtual void InsertWithHint(KeyHandle handle, void** hint) override {
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skip_list_.InsertWithHint(static_cast<char*>(handle), hint);
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}
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virtual bool InsertKeyWithHint(KeyHandle handle, void** hint) override {
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return skip_list_.InsertWithHint(static_cast<char*>(handle), hint);
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}
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virtual void InsertConcurrently(KeyHandle handle) override {
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skip_list_.InsertConcurrently(static_cast<char*>(handle));
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}
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virtual bool InsertKeyConcurrently(KeyHandle handle) override {
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return skip_list_.InsertConcurrently(static_cast<char*>(handle));
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}
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// Returns true iff an entry that compares equal to key is in the list.
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virtual bool Contains(const char* key) const override {
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return skip_list_.Contains(key);
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}
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virtual size_t ApproximateMemoryUsage() override {
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// All memory is allocated through allocator; nothing to report here
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return 0;
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}
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virtual void Get(const LookupKey& k, void* callback_args,
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bool (*callback_func)(void* arg,
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const char* entry)) override {
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SkipListRep::Iterator iter(&skip_list_);
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Slice dummy_slice;
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for (iter.Seek(dummy_slice, k.memtable_key().data());
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iter.Valid() && callback_func(callback_args, iter.key());
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iter.Next()) {
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}
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}
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uint64_t ApproximateNumEntries(const Slice& start_ikey,
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const Slice& end_ikey) override {
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std::string tmp;
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uint64_t start_count =
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skip_list_.EstimateCount(EncodeKey(&tmp, start_ikey));
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uint64_t end_count = skip_list_.EstimateCount(EncodeKey(&tmp, end_ikey));
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return (end_count >= start_count) ? (end_count - start_count) : 0;
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}
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virtual ~SkipListRep() override { }
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// Iteration over the contents of a skip list
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class Iterator : public MemTableRep::Iterator {
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InlineSkipList<const MemTableRep::KeyComparator&>::Iterator iter_;
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public:
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// Initialize an iterator over the specified list.
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// The returned iterator is not valid.
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explicit Iterator(
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const InlineSkipList<const MemTableRep::KeyComparator&>* list)
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: iter_(list) {}
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virtual ~Iterator() override { }
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// Returns true iff the iterator is positioned at a valid node.
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virtual bool Valid() const override {
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return iter_.Valid();
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}
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// Returns the key at the current position.
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// REQUIRES: Valid()
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virtual const char* key() const override {
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return iter_.key();
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}
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// Advances to the next position.
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// REQUIRES: Valid()
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virtual void Next() override {
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iter_.Next();
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}
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// Advances to the previous position.
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// REQUIRES: Valid()
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virtual void Prev() override {
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iter_.Prev();
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}
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// Advance to the first entry with a key >= target
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virtual void Seek(const Slice& user_key, const char* memtable_key)
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override {
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if (memtable_key != nullptr) {
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iter_.Seek(memtable_key);
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} else {
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iter_.Seek(EncodeKey(&tmp_, user_key));
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}
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}
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// Retreat to the last entry with a key <= target
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virtual void SeekForPrev(const Slice& user_key,
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const char* memtable_key) override {
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if (memtable_key != nullptr) {
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iter_.SeekForPrev(memtable_key);
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} else {
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iter_.SeekForPrev(EncodeKey(&tmp_, user_key));
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}
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}
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// Position at the first entry in list.
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// Final state of iterator is Valid() iff list is not empty.
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virtual void SeekToFirst() override {
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iter_.SeekToFirst();
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}
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// Position at the last entry in list.
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// Final state of iterator is Valid() iff list is not empty.
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virtual void SeekToLast() override {
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iter_.SeekToLast();
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}
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protected:
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std::string tmp_; // For passing to EncodeKey
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};
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// Iterator over the contents of a skip list which also keeps track of the
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// previously visited node. In Seek(), it examines a few nodes after it
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// first, falling back to O(log n) search from the head of the list only if
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// the target key hasn't been found.
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class LookaheadIterator : public MemTableRep::Iterator {
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public:
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explicit LookaheadIterator(const SkipListRep& rep) :
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rep_(rep), iter_(&rep_.skip_list_), prev_(iter_) {}
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virtual ~LookaheadIterator() override {}
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virtual bool Valid() const override {
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return iter_.Valid();
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}
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virtual const char *key() const override {
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assert(Valid());
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return iter_.key();
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}
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virtual void Next() override {
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assert(Valid());
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bool advance_prev = true;
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if (prev_.Valid()) {
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auto k1 = rep_.UserKey(prev_.key());
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auto k2 = rep_.UserKey(iter_.key());
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if (k1.compare(k2) == 0) {
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// same user key, don't move prev_
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advance_prev = false;
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} else if (rep_.transform_) {
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// only advance prev_ if it has the same prefix as iter_
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auto t1 = rep_.transform_->Transform(k1);
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auto t2 = rep_.transform_->Transform(k2);
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advance_prev = t1.compare(t2) == 0;
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}
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}
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if (advance_prev) {
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prev_ = iter_;
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}
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iter_.Next();
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}
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virtual void Prev() override {
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assert(Valid());
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iter_.Prev();
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prev_ = iter_;
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}
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virtual void Seek(const Slice& internal_key, const char *memtable_key)
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override {
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const char *encoded_key =
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(memtable_key != nullptr) ?
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memtable_key : EncodeKey(&tmp_, internal_key);
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if (prev_.Valid() && rep_.cmp_(encoded_key, prev_.key()) >= 0) {
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// prev_.key() is smaller or equal to our target key; do a quick
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// linear search (at most lookahead_ steps) starting from prev_
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iter_ = prev_;
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size_t cur = 0;
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while (cur++ <= rep_.lookahead_ && iter_.Valid()) {
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if (rep_.cmp_(encoded_key, iter_.key()) <= 0) {
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return;
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}
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Next();
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}
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}
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iter_.Seek(encoded_key);
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prev_ = iter_;
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}
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virtual void SeekForPrev(const Slice& internal_key,
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const char* memtable_key) override {
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const char* encoded_key = (memtable_key != nullptr)
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? memtable_key
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: EncodeKey(&tmp_, internal_key);
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iter_.SeekForPrev(encoded_key);
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prev_ = iter_;
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}
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virtual void SeekToFirst() override {
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iter_.SeekToFirst();
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prev_ = iter_;
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}
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virtual void SeekToLast() override {
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iter_.SeekToLast();
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prev_ = iter_;
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}
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protected:
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std::string tmp_; // For passing to EncodeKey
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private:
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const SkipListRep& rep_;
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InlineSkipList<const MemTableRep::KeyComparator&>::Iterator iter_;
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InlineSkipList<const MemTableRep::KeyComparator&>::Iterator prev_;
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};
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virtual MemTableRep::Iterator* GetIterator(Arena* arena = nullptr) override {
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if (lookahead_ > 0) {
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void *mem =
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arena ? arena->AllocateAligned(sizeof(SkipListRep::LookaheadIterator))
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: operator new(sizeof(SkipListRep::LookaheadIterator));
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return new (mem) SkipListRep::LookaheadIterator(*this);
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} else {
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void *mem =
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arena ? arena->AllocateAligned(sizeof(SkipListRep::Iterator))
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: operator new(sizeof(SkipListRep::Iterator));
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return new (mem) SkipListRep::Iterator(&skip_list_);
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}
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}
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};
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}
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MemTableRep* SkipListFactory::CreateMemTableRep(
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const MemTableRep::KeyComparator& compare, Allocator* allocator,
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const SliceTransform* transform, Logger* logger) {
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return new SkipListRep(compare, allocator, transform, lookahead_);
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}
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} // namespace rocksdb
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