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rocksdb/memtable/hash_skiplist_rep.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.
//
#ifndef ROCKSDB_LITE
#include "memtable/hash_skiplist_rep.h"
#include <atomic>
#include "rocksdb/memtablerep.h"
#include "util/arena.h"
#include "rocksdb/slice.h"
#include "rocksdb/slice_transform.h"
#include "port/port.h"
#include "util/murmurhash.h"
#include "db/memtable.h"
#include "db/skiplist.h"
namespace rocksdb {
namespace {
class HashSkipListRep : public MemTableRep {
public:
HashSkipListRep(const MemTableRep::KeyComparator& compare,
MemTableAllocator* allocator, const SliceTransform* transform,
size_t bucket_size, int32_t skiplist_height,
int32_t skiplist_branching_factor);
virtual void Insert(KeyHandle handle) override;
virtual bool Contains(const char* key) const override;
virtual size_t ApproximateMemoryUsage() override;
virtual void Get(const LookupKey& k, void* callback_args,
bool (*callback_func)(void* arg,
const char* entry)) override;
virtual ~HashSkipListRep();
virtual MemTableRep::Iterator* GetIterator(Arena* arena = nullptr) override;
virtual MemTableRep::Iterator* GetDynamicPrefixIterator(
Arena* arena = nullptr) override;
private:
friend class DynamicIterator;
typedef SkipList<const char*, const MemTableRep::KeyComparator&> Bucket;
size_t bucket_size_;
const int32_t skiplist_height_;
const int32_t skiplist_branching_factor_;
// Maps slices (which are transformed user keys) to buckets of keys sharing
// the same transform.
std::atomic<Bucket*>* buckets_;
// The user-supplied transform whose domain is the user keys.
const SliceTransform* transform_;
const MemTableRep::KeyComparator& compare_;
// immutable after construction
MemTableAllocator* const allocator_;
inline size_t GetHash(const Slice& slice) const {
return MurmurHash(slice.data(), static_cast<int>(slice.size()), 0) %
bucket_size_;
}
inline Bucket* GetBucket(size_t i) const {
return buckets_[i].load(std::memory_order_acquire);
}
inline Bucket* GetBucket(const Slice& slice) const {
return GetBucket(GetHash(slice));
}
// Get a bucket from buckets_. If the bucket hasn't been initialized yet,
// initialize it before returning.
Bucket* GetInitializedBucket(const Slice& transformed);
class Iterator : public MemTableRep::Iterator {
public:
explicit Iterator(Bucket* list, bool own_list = true,
Arena* arena = nullptr)
: list_(list), iter_(list), own_list_(own_list), arena_(arena) {}
virtual ~Iterator() {
// if we own the list, we should also delete it
if (own_list_) {
assert(list_ != nullptr);
delete list_;
}
}
// Returns true iff the iterator is positioned at a valid node.
virtual bool Valid() const override {
return list_ != nullptr && iter_.Valid();
}
// Returns the key at the current position.
// REQUIRES: Valid()
virtual const char* key() const override {
assert(Valid());
return iter_.key();
}
// Advances to the next position.
// REQUIRES: Valid()
virtual void Next() override {
assert(Valid());
iter_.Next();
}
// Advances to the previous position.
// REQUIRES: Valid()
virtual void Prev() override {
assert(Valid());
iter_.Prev();
}
// Advance to the first entry with a key >= target
virtual void Seek(const Slice& internal_key,
const char* memtable_key) override {
if (list_ != nullptr) {
const char* encoded_key =
(memtable_key != nullptr) ?
memtable_key : EncodeKey(&tmp_, internal_key);
iter_.Seek(encoded_key);
}
}
// Position at the first entry in collection.
// Final state of iterator is Valid() iff collection is not empty.
virtual void SeekToFirst() override {
if (list_ != nullptr) {
iter_.SeekToFirst();
}
}
// Position at the last entry in collection.
// Final state of iterator is Valid() iff collection is not empty.
virtual void SeekToLast() override {
if (list_ != nullptr) {
iter_.SeekToLast();
}
}
protected:
void Reset(Bucket* list) {
if (own_list_) {
assert(list_ != nullptr);
delete list_;
}
list_ = list;
iter_.SetList(list);
own_list_ = false;
}
private:
// if list_ is nullptr, we should NEVER call any methods on iter_
// if list_ is nullptr, this Iterator is not Valid()
Bucket* list_;
Bucket::Iterator iter_;
// here we track if we own list_. If we own it, we are also
// responsible for it's cleaning. This is a poor man's shared_ptr
bool own_list_;
std::unique_ptr<Arena> arena_;
std::string tmp_; // For passing to EncodeKey
};
class DynamicIterator : public HashSkipListRep::Iterator {
public:
explicit DynamicIterator(const HashSkipListRep& memtable_rep)
: HashSkipListRep::Iterator(nullptr, false),
memtable_rep_(memtable_rep) {}
// Advance to the first entry with a key >= target
virtual void Seek(const Slice& k, const char* memtable_key) override {
auto transformed = memtable_rep_.transform_->Transform(ExtractUserKey(k));
Reset(memtable_rep_.GetBucket(transformed));
HashSkipListRep::Iterator::Seek(k, memtable_key);
}
// Position at the first entry in collection.
// Final state of iterator is Valid() iff collection is not empty.
virtual void SeekToFirst() override {
// Prefix iterator does not support total order.
// We simply set the iterator to invalid state
Reset(nullptr);
}
// Position at the last entry in collection.
// Final state of iterator is Valid() iff collection is not empty.
virtual void SeekToLast() override {
// Prefix iterator does not support total order.
// We simply set the iterator to invalid state
Reset(nullptr);
}
private:
// the underlying memtable
const HashSkipListRep& memtable_rep_;
};
class EmptyIterator : public MemTableRep::Iterator {
// This is used when there wasn't a bucket. It is cheaper than
// instantiating an empty bucket over which to iterate.
public:
EmptyIterator() { }
virtual bool Valid() const override { return false; }
virtual const char* key() const override {
assert(false);
return nullptr;
}
virtual void Next() override {}
virtual void Prev() override {}
virtual void Seek(const Slice& internal_key,
const char* memtable_key) override {}
virtual void SeekToFirst() override {}
virtual void SeekToLast() override {}
private:
};
};
HashSkipListRep::HashSkipListRep(const MemTableRep::KeyComparator& compare,
MemTableAllocator* allocator,
const SliceTransform* transform,
size_t bucket_size, int32_t skiplist_height,
int32_t skiplist_branching_factor)
: MemTableRep(allocator),
bucket_size_(bucket_size),
skiplist_height_(skiplist_height),
skiplist_branching_factor_(skiplist_branching_factor),
transform_(transform),
compare_(compare),
allocator_(allocator) {
auto mem = allocator->AllocateAligned(
sizeof(std::atomic<void*>) * bucket_size);
buckets_ = new (mem) std::atomic<Bucket*>[bucket_size];
for (size_t i = 0; i < bucket_size_; ++i) {
buckets_[i].store(nullptr, std::memory_order_relaxed);
}
}
HashSkipListRep::~HashSkipListRep() {
}
HashSkipListRep::Bucket* HashSkipListRep::GetInitializedBucket(
const Slice& transformed) {
size_t hash = GetHash(transformed);
auto bucket = GetBucket(hash);
if (bucket == nullptr) {
auto addr = allocator_->AllocateAligned(sizeof(Bucket));
bucket = new (addr) Bucket(compare_, allocator_, skiplist_height_,
skiplist_branching_factor_);
buckets_[hash].store(bucket, std::memory_order_release);
}
return bucket;
}
void HashSkipListRep::Insert(KeyHandle handle) {
auto* key = static_cast<char*>(handle);
assert(!Contains(key));
auto transformed = transform_->Transform(UserKey(key));
auto bucket = GetInitializedBucket(transformed);
bucket->Insert(key);
}
bool HashSkipListRep::Contains(const char* key) const {
auto transformed = transform_->Transform(UserKey(key));
auto bucket = GetBucket(transformed);
if (bucket == nullptr) {
return false;
}
return bucket->Contains(key);
}
size_t HashSkipListRep::ApproximateMemoryUsage() {
return 0;
}
void HashSkipListRep::Get(const LookupKey& k, void* callback_args,
bool (*callback_func)(void* arg, const char* entry)) {
auto transformed = transform_->Transform(k.user_key());
auto bucket = GetBucket(transformed);
if (bucket != nullptr) {
Bucket::Iterator iter(bucket);
for (iter.Seek(k.memtable_key().data());
iter.Valid() && callback_func(callback_args, iter.key());
iter.Next()) {
}
}
}
MemTableRep::Iterator* HashSkipListRep::GetIterator(Arena* arena) {
// allocate a new arena of similar size to the one currently in use
Arena* new_arena = new Arena(allocator_->BlockSize());
auto list = new Bucket(compare_, new_arena);
for (size_t i = 0; i < bucket_size_; ++i) {
auto bucket = GetBucket(i);
if (bucket != nullptr) {
Bucket::Iterator itr(bucket);
for (itr.SeekToFirst(); itr.Valid(); itr.Next()) {
list->Insert(itr.key());
}
}
}
if (arena == nullptr) {
return new Iterator(list, true, new_arena);
} else {
auto mem = arena->AllocateAligned(sizeof(Iterator));
return new (mem) Iterator(list, true, new_arena);
}
}
MemTableRep::Iterator* HashSkipListRep::GetDynamicPrefixIterator(Arena* arena) {
if (arena == nullptr) {
return new DynamicIterator(*this);
} else {
auto mem = arena->AllocateAligned(sizeof(DynamicIterator));
return new (mem) DynamicIterator(*this);
}
}
} // anon namespace
MemTableRep* HashSkipListRepFactory::CreateMemTableRep(
const MemTableRep::KeyComparator& compare, MemTableAllocator* allocator,
const SliceTransform* transform, Logger* logger) {
return new HashSkipListRep(compare, allocator, transform, bucket_count_,
skiplist_height_, skiplist_branching_factor_);
}
MemTableRepFactory* NewHashSkipListRepFactory(
size_t bucket_count, int32_t skiplist_height,
int32_t skiplist_branching_factor) {
return new HashSkipListRepFactory(bucket_count, skiplist_height,
skiplist_branching_factor);
}
} // namespace rocksdb
#endif // ROCKSDB_LITE