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rocksdb/memtable/skiplistrep.cc

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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
#include "db/inlineskiplist.h"
#include "db/memtable.h"
#include "rocksdb/memtablerep.h"
#include "util/arena.h"
namespace rocksdb {
namespace {
class SkipListRep : public MemTableRep {
InlineSkipList<const MemTableRep::KeyComparator&> skip_list_;
const MemTableRep::KeyComparator& cmp_;
const SliceTransform* transform_;
const size_t lookahead_;
friend class LookaheadIterator;
public:
explicit SkipListRep(const MemTableRep::KeyComparator& compare,
MemTableAllocator* allocator,
const SliceTransform* transform, const size_t lookahead)
: MemTableRep(allocator), skip_list_(compare, allocator), cmp_(compare),
transform_(transform), lookahead_(lookahead) {
}
virtual bool IsInsertConcurrentlySupported() const override { return true; }
virtual KeyHandle Allocate(const size_t len, char** buf) override {
*buf = skip_list_.AllocateKey(len);
return static_cast<KeyHandle>(*buf);
}
// Insert key into the list.
// REQUIRES: nothing that compares equal to key is currently in the list.
virtual void Insert(KeyHandle handle) override {
skip_list_.Insert(static_cast<char*>(handle));
}
virtual void InsertConcurrently(KeyHandle handle) override {
skip_list_.InsertConcurrently(static_cast<char*>(handle));
}
// Returns true iff an entry that compares equal to key is in the list.
virtual bool Contains(const char* key) const override {
return skip_list_.Contains(key);
}
virtual size_t ApproximateMemoryUsage() override {
// All memory is allocated through allocator; nothing to report here
return 0;
}
virtual void Get(const LookupKey& k, void* callback_args,
bool (*callback_func)(void* arg,
const char* entry)) override {
SkipListRep::Iterator iter(&skip_list_);
Slice dummy_slice;
for (iter.Seek(dummy_slice, k.memtable_key().data());
iter.Valid() && callback_func(callback_args, iter.key());
iter.Next()) {
}
}
uint64_t ApproximateNumEntries(const Slice& start_ikey,
const Slice& end_ikey) override {
std::string tmp;
uint64_t start_count =
skip_list_.EstimateCount(EncodeKey(&tmp, start_ikey));
uint64_t end_count = skip_list_.EstimateCount(EncodeKey(&tmp, end_ikey));
return (end_count >= start_count) ? (end_count - start_count) : 0;
}
virtual ~SkipListRep() override { }
// Iteration over the contents of a skip list
class Iterator : public MemTableRep::Iterator {
InlineSkipList<const MemTableRep::KeyComparator&>::Iterator iter_;
public:
// Initialize an iterator over the specified list.
// The returned iterator is not valid.
explicit Iterator(
const InlineSkipList<const MemTableRep::KeyComparator&>* list)
: iter_(list) {}
virtual ~Iterator() override { }
// Returns true iff the iterator is positioned at a valid node.
virtual bool Valid() const override {
return iter_.Valid();
}
// Returns the key at the current position.
// REQUIRES: Valid()
virtual const char* key() const override {
return iter_.key();
}
// Advances to the next position.
// REQUIRES: Valid()
virtual void Next() override {
iter_.Next();
}
// Advances to the previous position.
// REQUIRES: Valid()
virtual void Prev() override {
iter_.Prev();
}
// Advance to the first entry with a key >= target
virtual void Seek(const Slice& user_key, const char* memtable_key)
override {
if (memtable_key != nullptr) {
iter_.Seek(memtable_key);
} else {
iter_.Seek(EncodeKey(&tmp_, user_key));
}
}
// Position at the first entry in list.
// Final state of iterator is Valid() iff list is not empty.
virtual void SeekToFirst() override {
iter_.SeekToFirst();
}
// Position at the last entry in list.
// Final state of iterator is Valid() iff list is not empty.
virtual void SeekToLast() override {
iter_.SeekToLast();
}
protected:
std::string tmp_; // For passing to EncodeKey
};
// Iterator over the contents of a skip list which also keeps track of the
// previously visited node. In Seek(), it examines a few nodes after it
// first, falling back to O(log n) search from the head of the list only if
// the target key hasn't been found.
class LookaheadIterator : public MemTableRep::Iterator {
public:
explicit LookaheadIterator(const SkipListRep& rep) :
rep_(rep), iter_(&rep_.skip_list_), prev_(iter_) {}
virtual ~LookaheadIterator() override {}
virtual bool Valid() const override {
return iter_.Valid();
}
virtual const char *key() const override {
assert(Valid());
return iter_.key();
}
virtual void Next() override {
assert(Valid());
bool advance_prev = true;
if (prev_.Valid()) {
auto k1 = rep_.UserKey(prev_.key());
auto k2 = rep_.UserKey(iter_.key());
if (k1.compare(k2) == 0) {
// same user key, don't move prev_
advance_prev = false;
} else if (rep_.transform_) {
// only advance prev_ if it has the same prefix as iter_
auto t1 = rep_.transform_->Transform(k1);
auto t2 = rep_.transform_->Transform(k2);
advance_prev = t1.compare(t2) == 0;
}
}
if (advance_prev) {
prev_ = iter_;
}
iter_.Next();
}
virtual void Prev() override {
assert(Valid());
iter_.Prev();
prev_ = iter_;
}
virtual void Seek(const Slice& internal_key, const char *memtable_key)
override {
const char *encoded_key =
(memtable_key != nullptr) ?
memtable_key : EncodeKey(&tmp_, internal_key);
if (prev_.Valid() && rep_.cmp_(encoded_key, prev_.key()) >= 0) {
// prev_.key() is smaller or equal to our target key; do a quick
// linear search (at most lookahead_ steps) starting from prev_
iter_ = prev_;
size_t cur = 0;
while (cur++ <= rep_.lookahead_ && iter_.Valid()) {
if (rep_.cmp_(encoded_key, iter_.key()) <= 0) {
return;
}
Next();
}
}
iter_.Seek(encoded_key);
prev_ = iter_;
}
virtual void SeekToFirst() override {
iter_.SeekToFirst();
prev_ = iter_;
}
virtual void SeekToLast() override {
iter_.SeekToLast();
prev_ = iter_;
}
protected:
std::string tmp_; // For passing to EncodeKey
private:
const SkipListRep& rep_;
InlineSkipList<const MemTableRep::KeyComparator&>::Iterator iter_;
InlineSkipList<const MemTableRep::KeyComparator&>::Iterator prev_;
};
virtual MemTableRep::Iterator* GetIterator(Arena* arena = nullptr) override {
if (lookahead_ > 0) {
void *mem =
arena ? arena->AllocateAligned(sizeof(SkipListRep::LookaheadIterator))
: operator new(sizeof(SkipListRep::LookaheadIterator));
return new (mem) SkipListRep::LookaheadIterator(*this);
} else {
void *mem =
arena ? arena->AllocateAligned(sizeof(SkipListRep::Iterator))
: operator new(sizeof(SkipListRep::Iterator));
return new (mem) SkipListRep::Iterator(&skip_list_);
}
}
};
}
MemTableRep* SkipListFactory::CreateMemTableRep(
const MemTableRep::KeyComparator& compare, MemTableAllocator* allocator,
const SliceTransform* transform, Logger* logger) {
return new SkipListRep(compare, allocator, transform, lookahead_);
}
} // namespace rocksdb