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rocksdb/util/hash_linklist_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.
//
#include "util/hash_linklist_rep.h"
#include "rocksdb/memtablerep.h"
#include "util/arena.h"
#include "rocksdb/slice.h"
#include "rocksdb/slice_transform.h"
#include "port/port.h"
#include "port/atomic_pointer.h"
#include "util/murmurhash.h"
#include "db/memtable.h"
#include "db/skiplist.h"
namespace rocksdb {
namespace {
typedef const char* Key;
struct Node {
explicit Node(const Key& k) :
key(k) {
}
Key const key;
// Accessors/mutators for links. Wrapped in methods so we can
// add the appropriate barriers as necessary.
Node* Next() {
// Use an 'acquire load' so that we observe a fully initialized
// version of the returned Node.
return reinterpret_cast<Node*>(next_.Acquire_Load());
}
void SetNext(Node* x) {
// Use a 'release store' so that anybody who reads through this
// pointer observes a fully initialized version of the inserted node.
next_.Release_Store(x);
}
// No-barrier variants that can be safely used in a few locations.
Node* NoBarrier_Next() {
return reinterpret_cast<Node*>(next_.NoBarrier_Load());
}
void NoBarrier_SetNext(Node* x) {
next_.NoBarrier_Store(x);
}
private:
port::AtomicPointer next_;
};
class HashLinkListRep : public MemTableRep {
public:
HashLinkListRep(MemTableRep::KeyComparator& compare, Arena* arena,
const SliceTransform* transform, size_t bucket_size);
virtual void Insert(const char* key) override;
virtual bool Contains(const char* key) const override;
virtual size_t ApproximateMemoryUsage() override;
virtual ~HashLinkListRep();
virtual MemTableRep::Iterator* GetIterator() override;
virtual MemTableRep::Iterator* GetIterator(const Slice& slice) override;
virtual MemTableRep::Iterator* GetPrefixIterator(const Slice& prefix)
override;
virtual MemTableRep::Iterator* GetDynamicPrefixIterator() override;
private:
friend class DynamicIterator;
typedef SkipList<const char*, MemTableRep::KeyComparator&> FullList;
size_t bucket_size_;
// Maps slices (which are transformed user keys) to buckets of keys sharing
// the same transform.
port::AtomicPointer* buckets_;
// The user-supplied transform whose domain is the user keys.
const SliceTransform* transform_;
MemTableRep::KeyComparator& compare_;
// immutable after construction
Arena* const arena_;
bool BucketContains(Node* head, const Slice& key) const;
Slice GetPrefix(const Slice& internal_key) const {
return transform_->Transform(ExtractUserKey(internal_key));
}
size_t GetHash(const Slice& slice) const {
return MurmurHash(slice.data(), slice.size(), 0) % bucket_size_;
}
Node* GetBucket(size_t i) const {
return static_cast<Node*>(buckets_[i].Acquire_Load());
}
Node* GetBucket(const Slice& slice) const {
return GetBucket(GetHash(slice));
}
Node* NewNode(const Key& key) {
char* mem = arena_->AllocateAligned(sizeof(Node));
return new (mem) Node(key);
}
bool Equal(const Slice& a, const Key& b) const {
return (compare_(b, a) == 0);
}
bool Equal(const Key& a, const Key& b) const { return (compare_(a, b) == 0); }
bool KeyIsAfterNode(const Slice& internal_key, const Node* n) const {
// nullptr n is considered infinite
return (n != nullptr) && (compare_(n->key, internal_key) < 0);
}
bool KeyIsAfterNode(const Key& key, const Node* n) const {
// nullptr n is considered infinite
return (n != nullptr) && (compare_(n->key, key) < 0);
}
Node* FindGreaterOrEqualInBucket(Node* head, const Slice& key) const;
class FullListIterator : public MemTableRep::Iterator {
public:
explicit FullListIterator(FullList* list)
: iter_(list), full_list_(list) {}
virtual ~FullListIterator() {
}
// Returns true iff the iterator is positioned at a valid node.
virtual bool Valid() const {
return iter_.Valid();
}
// Returns the key at the current position.
// REQUIRES: Valid()
virtual const char* key() const {
assert(Valid());
return iter_.key();
}
// Advances to the next position.
// REQUIRES: Valid()
virtual void Next() {
assert(Valid());
iter_.Next();
}
// Advances to the previous position.
// REQUIRES: Valid()
virtual void Prev() {
assert(Valid());
iter_.Prev();
}
// Advance to the first entry with a key >= target
virtual void Seek(const Slice& internal_key, const char* memtable_key) {
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() {
iter_.SeekToFirst();
}
// Position at the last entry in collection.
// Final state of iterator is Valid() iff collection is not empty.
virtual void SeekToLast() {
iter_.SeekToLast();
}
private:
FullList::Iterator iter_;
// To destruct with the iterator.
std::unique_ptr<FullList> full_list_;
std::string tmp_; // For passing to EncodeKey
};
class Iterator : public MemTableRep::Iterator {
public:
explicit Iterator(const HashLinkListRep* const hash_link_list_rep,
Node* head) :
hash_link_list_rep_(hash_link_list_rep), head_(head), node_(nullptr) {
}
virtual ~Iterator() {
}
// Returns true iff the iterator is positioned at a valid node.
virtual bool Valid() const {
return node_ != nullptr;
}
// Returns the key at the current position.
// REQUIRES: Valid()
virtual const char* key() const {
assert(Valid());
return node_->key;
}
// Advances to the next position.
// REQUIRES: Valid()
virtual void Next() {
assert(Valid());
node_ = node_->Next();
}
// Advances to the previous position.
// REQUIRES: Valid()
virtual void Prev() {
// Prefix iterator does not support total order.
// We simply set the iterator to invalid state
Reset(nullptr);
}
// Advance to the first entry with a key >= target
virtual void Seek(const Slice& internal_key, const char* memtable_key) {
node_ = hash_link_list_rep_->FindGreaterOrEqualInBucket(head_,
internal_key);
}
// Position at the first entry in collection.
// Final state of iterator is Valid() iff collection is not empty.
virtual void SeekToFirst() {
// 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() {
// Prefix iterator does not support total order.
// We simply set the iterator to invalid state
Reset(nullptr);
}
protected:
void Reset(Node* head) {
head_ = head;
node_ = nullptr;
}
private:
friend class HashLinkListRep;
const HashLinkListRep* const hash_link_list_rep_;
Node* head_;
Node* node_;
std::string tmp_; // For passing to EncodeKey
virtual void SeekToHead() {
node_ = head_;
}
};
class DynamicIterator : public HashLinkListRep::Iterator {
public:
explicit DynamicIterator(HashLinkListRep& memtable_rep)
: HashLinkListRep::Iterator(&memtable_rep, nullptr),
memtable_rep_(memtable_rep) {}
// Advance to the first entry with a key >= target
virtual void Seek(const Slice& k, const char* memtable_key) {
auto transformed = memtable_rep_.GetPrefix(k);
Reset(memtable_rep_.GetBucket(transformed));
HashLinkListRep::Iterator::Seek(k, memtable_key);
}
private:
// the underlying memtable
const HashLinkListRep& 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 {
return false;
}
virtual const char* key() const {
assert(false);
return nullptr;
}
virtual void Next() { }
virtual void Prev() { }
virtual void Seek(const Slice& user_key, const char* memtable_key) { }
virtual void SeekToFirst() { }
virtual void SeekToLast() { }
private:
};
};
HashLinkListRep::HashLinkListRep(MemTableRep::KeyComparator& compare,
Arena* arena, const SliceTransform* transform,
size_t bucket_size)
: bucket_size_(bucket_size),
transform_(transform),
compare_(compare),
arena_(arena) {
char* mem = arena_->AllocateAligned(
sizeof(port::AtomicPointer) * bucket_size);
buckets_ = new (mem) port::AtomicPointer[bucket_size];
for (size_t i = 0; i < bucket_size_; ++i) {
buckets_[i].NoBarrier_Store(nullptr);
}
}
HashLinkListRep::~HashLinkListRep() {
}
void HashLinkListRep::Insert(const char* key) {
assert(!Contains(key));
Slice internal_key = GetLengthPrefixedSlice(key);
auto transformed = GetPrefix(internal_key);
auto& bucket = buckets_[GetHash(transformed)];
Node* head = static_cast<Node*>(bucket.Acquire_Load());
if (!head) {
Node* x = NewNode(key);
// NoBarrier_SetNext() suffices since we will add a barrier when
// we publish a pointer to "x" in prev[i].
x->NoBarrier_SetNext(nullptr);
bucket.Release_Store(static_cast<void*>(x));
return;
}
Node* cur = head;
Node* prev = nullptr;
while (true) {
if (cur == nullptr) {
break;
}
Node* next = cur->Next();
// Make sure the lists are sorted.
// If x points to head_ or next points nullptr, it is trivially satisfied.
assert((cur == head) || (next == nullptr) ||
KeyIsAfterNode(next->key, cur));
if (KeyIsAfterNode(internal_key, cur)) {
// Keep searching in this list
prev = cur;
cur = next;
} else {
break;
}
}
// Our data structure does not allow duplicate insertion
assert(cur == nullptr || !Equal(key, cur->key));
Node* x = NewNode(key);
// NoBarrier_SetNext() suffices since we will add a barrier when
// we publish a pointer to "x" in prev[i].
x->NoBarrier_SetNext(cur);
if (prev) {
prev->SetNext(x);
} else {
bucket.Release_Store(static_cast<void*>(x));
}
}
bool HashLinkListRep::Contains(const char* key) const {
Slice internal_key = GetLengthPrefixedSlice(key);
auto transformed = GetPrefix(internal_key);
auto bucket = GetBucket(transformed);
if (bucket == nullptr) {
return false;
}
return BucketContains(bucket, internal_key);
}
size_t HashLinkListRep::ApproximateMemoryUsage() {
// Memory is always allocated from the arena.
return 0;
}
MemTableRep::Iterator* HashLinkListRep::GetIterator() {
auto list = new FullList(compare_, arena_);
for (size_t i = 0; i < bucket_size_; ++i) {
auto bucket = GetBucket(i);
if (bucket != nullptr) {
Iterator itr(this, bucket);
for (itr.SeekToHead(); itr.Valid(); itr.Next()) {
list->Insert(itr.key());
}
}
}
return new FullListIterator(list);
}
MemTableRep::Iterator* HashLinkListRep::GetPrefixIterator(
const Slice& prefix) {
auto bucket = GetBucket(prefix);
if (bucket == nullptr) {
return new EmptyIterator();
}
return new Iterator(this, bucket);
}
MemTableRep::Iterator* HashLinkListRep::GetIterator(const Slice& slice) {
return GetPrefixIterator(transform_->Transform(slice));
}
MemTableRep::Iterator* HashLinkListRep::GetDynamicPrefixIterator() {
return new DynamicIterator(*this);
}
bool HashLinkListRep::BucketContains(Node* head, const Slice& user_key) const {
Node* x = FindGreaterOrEqualInBucket(head, user_key);
return (x != nullptr && Equal(user_key, x->key));
}
Node* HashLinkListRep::FindGreaterOrEqualInBucket(Node* head,
const Slice& key) const {
Node* x = head;
while (true) {
if (x == nullptr) {
return x;
}
Node* next = x->Next();
// Make sure the lists are sorted.
// If x points to head_ or next points nullptr, it is trivially satisfied.
assert((x == head) || (next == nullptr) || KeyIsAfterNode(next->key, x));
if (KeyIsAfterNode(key, x)) {
// Keep searching in this list
x = next;
} else {
break;
}
}
return x;
}
} // anon namespace
MemTableRep* HashLinkListRepFactory::CreateMemTableRep(
MemTableRep::KeyComparator& compare, Arena* arena) {
return new HashLinkListRep(compare, arena, transform_, bucket_count_);
}
MemTableRepFactory* NewHashLinkListRepFactory(
const SliceTransform* transform, size_t bucket_count) {
return new HashLinkListRepFactory(transform, bucket_count);
}
} // namespace rocksdb