rocksdb/db/memtable.cc
Naman Gupta fe25070242 In-place updates for equal keys and similar sized values
Summary:
Currently for each put, a fresh memory is allocated, and a new entry is added to the memtable with a new sequence number irrespective of whether the key already exists in the memtable. This diff is an attempt to update the value inplace for existing keys. It currently handles a very simple case:
1. Key already exists in the current memtable. Does not inplace update values in immutable memtable or snapshot
2. Latest value type is a 'put' ie kTypeValue
3. New value size is less than existing value, to avoid reallocating memory

TODO: For a put of an existing key, deallocate memory take by values, for other value types till a kTypeValue is found, ie. remove kTypeMerge.
TODO: Update the transaction log, to allow consistent reload of the memtable.

Test Plan: Added a unit test verifying the inplace update. But some other unit tests broken due to invalid sequence number checks. WIll fix them next.

Reviewers: xinyaohu, sumeet, haobo, dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D12423

Automatic commit by arc
2013-10-31 11:27:12 -07:00

330 lines
11 KiB
C++

// 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.
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#include "db/memtable.h"
#include <memory>
#include "db/dbformat.h"
#include "rocksdb/comparator.h"
#include "rocksdb/env.h"
#include "rocksdb/iterator.h"
#include "rocksdb/merge_operator.h"
#include "util/coding.h"
#include "util/mutexlock.h"
#include "util/murmurhash.h"
namespace std {
template <>
struct hash<rocksdb::Slice> {
size_t operator()(const rocksdb::Slice& slice) const {
return MurmurHash(slice.data(), slice.size(), 0);
}
};
}
namespace rocksdb {
MemTable::MemTable(const InternalKeyComparator& cmp,
std::shared_ptr<MemTableRepFactory> table_factory,
int numlevel,
const Options& options)
: comparator_(cmp),
refs_(0),
arena_impl_(options.arena_block_size),
table_(table_factory->CreateMemTableRep(comparator_, &arena_impl_)),
flush_in_progress_(false),
flush_completed_(false),
file_number_(0),
edit_(numlevel),
first_seqno_(0),
mem_next_logfile_number_(0),
mem_logfile_number_(0),
locks_(options.inplace_update_support
? options.inplace_update_num_locks
: 0) { }
MemTable::~MemTable() {
assert(refs_ == 0);
}
size_t MemTable::ApproximateMemoryUsage() {
return arena_impl_.ApproximateMemoryUsage() +
table_->ApproximateMemoryUsage();
}
int MemTable::KeyComparator::operator()(const char* aptr, const char* bptr)
const {
// Internal keys are encoded as length-prefixed strings.
Slice a = GetLengthPrefixedSlice(aptr);
Slice b = GetLengthPrefixedSlice(bptr);
return comparator.Compare(a, b);
}
Slice MemTableRep::UserKey(const char* key) const {
Slice slice = GetLengthPrefixedSlice(key);
return Slice(slice.data(), slice.size() - 8);
}
// Encode a suitable internal key target for "target" and return it.
// Uses *scratch as scratch space, and the returned pointer will point
// into this scratch space.
static const char* EncodeKey(std::string* scratch, const Slice& target) {
scratch->clear();
PutVarint32(scratch, target.size());
scratch->append(target.data(), target.size());
return scratch->data();
}
class MemTableIterator: public Iterator {
public:
explicit MemTableIterator(MemTableRep* table)
: iter_(table->GetIterator()) { }
MemTableIterator(MemTableRep* table, const Slice* prefix)
: iter_(table->GetPrefixIterator(*prefix)) { }
virtual bool Valid() const { return iter_->Valid(); }
virtual void Seek(const Slice& k) { iter_->Seek(EncodeKey(&tmp_, k)); }
virtual void SeekToFirst() { iter_->SeekToFirst(); }
virtual void SeekToLast() { iter_->SeekToLast(); }
virtual void Next() { iter_->Next(); }
virtual void Prev() { iter_->Prev(); }
virtual Slice key() const {
return GetLengthPrefixedSlice(iter_->key());
}
virtual Slice value() const {
Slice key_slice = GetLengthPrefixedSlice(iter_->key());
return GetLengthPrefixedSlice(key_slice.data() + key_slice.size());
}
virtual Status status() const { return Status::OK(); }
private:
std::shared_ptr<MemTableRep::Iterator> iter_;
std::string tmp_; // For passing to EncodeKey
// No copying allowed
MemTableIterator(const MemTableIterator&);
void operator=(const MemTableIterator&);
};
Iterator* MemTable::NewIterator(const Slice* prefix) {
if (prefix) {
return new MemTableIterator(table_.get(), prefix);
} else {
return new MemTableIterator(table_.get());
}
}
port::RWMutex* MemTable::GetLock(const Slice& key) {
return &locks_[std::hash<Slice>()(key) % locks_.size()];
}
void MemTable::Add(SequenceNumber s, ValueType type,
const Slice& key,
const Slice& value) {
// Format of an entry is concatenation of:
// key_size : varint32 of internal_key.size()
// key bytes : char[internal_key.size()]
// value_size : varint32 of value.size()
// value bytes : char[value.size()]
size_t key_size = key.size();
size_t val_size = value.size();
size_t internal_key_size = key_size + 8;
const size_t encoded_len =
VarintLength(internal_key_size) + internal_key_size +
VarintLength(val_size) + val_size;
char* buf = arena_impl_.Allocate(encoded_len);
char* p = EncodeVarint32(buf, internal_key_size);
memcpy(p, key.data(), key_size);
p += key_size;
EncodeFixed64(p, (s << 8) | type);
p += 8;
p = EncodeVarint32(p, val_size);
memcpy(p, value.data(), val_size);
assert((p + val_size) - buf == (unsigned)encoded_len);
table_->Insert(buf);
// The first sequence number inserted into the memtable
assert(first_seqno_ == 0 || s > first_seqno_);
if (first_seqno_ == 0) {
first_seqno_ = s;
}
}
bool MemTable::Get(const LookupKey& key, std::string* value, Status* s,
std::deque<std::string>* operands, const Options& options) {
Slice memkey = key.memtable_key();
std::shared_ptr<MemTableRep::Iterator> iter(
table_->GetIterator(key.user_key()));
iter->Seek(memkey.data());
// It is the caller's responsibility to allocate/delete operands list
assert(operands != nullptr);
bool merge_in_progress = s->IsMergeInProgress();
auto merge_operator = options.merge_operator.get();
auto logger = options.info_log;
std::string merge_result;
for (; iter->Valid(); iter->Next()) {
// entry format is:
// klength varint32
// userkey char[klength-8]
// tag uint64
// vlength varint32
// value char[vlength]
// Check that it belongs to same user key. We do not check the
// sequence number since the Seek() call above should have skipped
// all entries with overly large sequence numbers.
const char* entry = iter->key();
uint32_t key_length;
const char* key_ptr = GetVarint32Ptr(entry, entry + 5, &key_length);
if (comparator_.comparator.user_comparator()->Compare(
Slice(key_ptr, key_length - 8), key.user_key()) == 0) {
// Correct user key
const uint64_t tag = DecodeFixed64(key_ptr + key_length - 8);
switch (static_cast<ValueType>(tag & 0xff)) {
case kTypeValue: {
if (options.inplace_update_support) {
GetLock(key.user_key())->ReadLock();
}
Slice v = GetLengthPrefixedSlice(key_ptr + key_length);
*s = Status::OK();
if (merge_in_progress) {
assert(merge_operator);
if (!merge_operator->FullMerge(key.user_key(), &v, *operands,
value, logger.get())) {
RecordTick(options.statistics, NUMBER_MERGE_FAILURES);
*s = Status::Corruption("Error: Could not perform merge.");
}
} else {
value->assign(v.data(), v.size());
}
if (options.inplace_update_support) {
GetLock(key.user_key())->Unlock();
}
return true;
}
case kTypeDeletion: {
if (merge_in_progress) {
assert(merge_operator);
*s = Status::OK();
if (!merge_operator->FullMerge(key.user_key(), nullptr, *operands,
value, logger.get())) {
RecordTick(options.statistics, NUMBER_MERGE_FAILURES);
*s = Status::Corruption("Error: Could not perform merge.");
}
} else {
*s = Status::NotFound(Slice());
}
return true;
}
case kTypeMerge: {
Slice v = GetLengthPrefixedSlice(key_ptr + key_length);
merge_in_progress = true;
operands->push_front(v.ToString());
while(operands->size() >= 2) {
// Attempt to associative merge. (Returns true if successful)
if (merge_operator->PartialMerge(key.user_key(),
Slice((*operands)[0]),
Slice((*operands)[1]),
&merge_result,
logger.get())) {
operands->pop_front();
swap(operands->front(), merge_result);
} else {
// Stack them because user can't associative merge
break;
}
}
break;
}
case kTypeLogData:
assert(false);
break;
}
} else {
// exit loop if user key does not match
break;
}
}
// No change to value, since we have not yet found a Put/Delete
if (merge_in_progress) {
*s = Status::MergeInProgress("");
}
return false;
}
bool MemTable::Update(SequenceNumber seq, ValueType type,
const Slice& key,
const Slice& value) {
LookupKey lkey(key, seq);
Slice memkey = lkey.memtable_key();
std::shared_ptr<MemTableRep::Iterator> iter(
table_.get()->GetIterator(lkey.user_key()));
iter->Seek(memkey.data());
if (iter->Valid()) {
// entry format is:
// klength varint32
// userkey char[klength-8]
// tag uint64
// vlength varint32
// value char[vlength]
// Check that it belongs to same user key. We do not check the
// sequence number since the Seek() call above should have skipped
// all entries with overly large sequence numbers.
const char* entry = iter->key();
uint32_t key_length;
const char* key_ptr = GetVarint32Ptr(entry, entry + 5, &key_length);
if (comparator_.comparator.user_comparator()->Compare(
Slice(key_ptr, key_length - 8), lkey.user_key()) == 0) {
// Correct user key
const uint64_t tag = DecodeFixed64(key_ptr + key_length - 8);
switch (static_cast<ValueType>(tag & 0xff)) {
case kTypeValue: {
uint32_t vlength;
GetVarint32Ptr(key_ptr + key_length,
key_ptr + key_length+5, &vlength);
// Update value, if newValue size <= curValue size
if (value.size() <= vlength) {
char* p = EncodeVarint32(const_cast<char*>(key_ptr) + key_length,
value.size());
WriteLock wl(GetLock(lkey.user_key()));
memcpy(p, value.data(), value.size());
assert(
(p + value.size()) - entry ==
(unsigned) (VarintLength(key_length) +
key_length +
VarintLength(value.size()) +
value.size())
);
return true;
}
}
default:
// If the latest value is kTypeDeletion, kTypeMerge or kTypeLogData
// then we probably don't have enough space to update in-place
// Maybe do something later
// Return false, and do normal Add()
return false;
}
}
}
// Key doesn't exist
return false;
}
} // namespace rocksdb