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rocksdb/db/memtable.cc
Naman Gupta 1447bb5919 Allow callback to change size of existing value. Change return type of the callback function to an enum status to handle 3 cases. 
Summary:
This diff fixes 2 hacks:
* The callback function can modify the existing value inplace, if the merged value fits within the existing buffer size. But currently the existing buffer size is not being modified. Now the callback recieves a int* allowing the size to be modified. Since size is encoded as a varint in the internal key for memtable. It might happen that the entire value might have be copied to the new location if the new size varint is smaller than the existing size varint.
* The callback function has 3 functionalities
    1. Modify existing buffer inplace, and update size correspondingly. Now to indicate that, Returns 1.
    2. Generate a new buffer indicating merged value. Returns 2.
    3. Fails to do either of above, based on whatever application logic. Returns 0.

Test Plan: Just make all for now. I'm adding another unit test to test each scenario.

Reviewers: dhruba, haobo

Reviewed By: haobo

CC: leveldb, sdong, kailiu, xinyaohu, sumeet, danguo

Differential Revision: https://reviews.facebook.net/D15195
2014-01-16 15:12:39 -08:00

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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.
//
// 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 "db/merge_context.h"
#include "rocksdb/comparator.h"
#include "rocksdb/env.h"
#include "rocksdb/iterator.h"
#include "rocksdb/merge_operator.h"
#include "util/coding.h"
#include "util/murmurhash.h"
#include "util/mutexlock.h"
#include "util/perf_context_imp.h"
#include "util/statistics_imp.h"
#include "util/stop_watch.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, const Options& options)
: comparator_(cmp),
refs_(0),
arena_impl_(options.arena_block_size),
table_(options.memtable_factory->CreateMemTableRep(comparator_,
&arena_impl_)),
flush_in_progress_(false),
flush_completed_(false),
file_number_(0),
first_seqno_(0),
mem_next_logfile_number_(0),
mem_logfile_number_(0),
locks_(options.inplace_update_support ? options.inplace_update_num_locks
: 0),
prefix_extractor_(options.prefix_extractor) {
if (prefix_extractor_ && options.memtable_prefix_bloom_bits > 0) {
prefix_bloom_.reset(new DynamicBloom(options.memtable_prefix_bloom_bits,
options.memtable_prefix_bloom_probes));
}
}
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.
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:
MemTableIterator(const MemTable& mem, const ReadOptions& options)
: mem_(mem), iter_(), dynamic_prefix_seek_(false), valid_(false) {
if (options.prefix) {
iter_.reset(mem_.table_->GetPrefixIterator(*options.prefix));
} else if (options.prefix_seek) {
iter_.reset(mem_.table_->GetDynamicPrefixIterator());
} else {
iter_.reset(mem_.table_->GetIterator());
}
}
virtual bool Valid() const { return valid_; }
virtual void Seek(const Slice& k) {
if (dynamic_prefix_seek_ && mem_.prefix_bloom_ &&
!mem_.prefix_bloom_->MayContain(
mem_.prefix_extractor_->Transform(ExtractUserKey(k)))) {
valid_ = false;
return;
}
iter_->Seek(k, nullptr);
valid_ = iter_->Valid();
}
virtual void SeekToFirst() {
iter_->SeekToFirst();
valid_ = iter_->Valid();
}
virtual void SeekToLast() {
iter_->SeekToLast();
valid_ = iter_->Valid();
}
virtual void Next() {
assert(Valid());
iter_->Next();
valid_ = iter_->Valid();
}
virtual void Prev() {
assert(Valid());
iter_->Prev();
valid_ = iter_->Valid();
}
virtual Slice key() const {
assert(Valid());
return GetLengthPrefixedSlice(iter_->key());
}
virtual Slice value() const {
assert(Valid());
Slice key_slice = GetLengthPrefixedSlice(iter_->key());
return GetLengthPrefixedSlice(key_slice.data() + key_slice.size());
}
virtual Status status() const { return Status::OK(); }
private:
const MemTable& mem_;
std::shared_ptr<MemTableRep::Iterator> iter_;
bool dynamic_prefix_seek_;
bool valid_;
// No copying allowed
MemTableIterator(const MemTableIterator&);
void operator=(const MemTableIterator&);
};
Iterator* MemTable::NewIterator(const ReadOptions& options) {
return new MemTableIterator(*this, options);
}
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, /* user 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);
if (prefix_bloom_) {
assert(prefix_extractor_);
prefix_bloom_->Add(prefix_extractor_->Transform(key));
}
// 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,
MergeContext& merge_context, const Options& options) {
StopWatchNano memtable_get_timer(options.env, false);
StartPerfTimer(&memtable_get_timer);
Slice mem_key = key.memtable_key();
Slice user_key = key.user_key();
std::unique_ptr<MemTableRep::Iterator> iter;
if (prefix_bloom_ &&
!prefix_bloom_->MayContain(prefix_extractor_->Transform(user_key))) {
// iter is null if prefix bloom says the key does not exist
} else {
iter.reset(table_->GetIterator(user_key));
iter->Seek(user_key, mem_key.data());
}
bool merge_in_progress = s->IsMergeInProgress();
auto merge_operator = options.merge_operator.get();
auto logger = options.info_log;
std::string merge_result;
bool found_final_value = false;
for (; !found_final_value && iter && 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,
merge_context.GetOperands(), value,
logger.get())) {
RecordTick(options.statistics.get(), 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();
}
found_final_value = true;
break;
}
case kTypeDeletion: {
if (merge_in_progress) {
assert(merge_operator);
*s = Status::OK();
if (!merge_operator->FullMerge(key.user_key(), nullptr,
merge_context.GetOperands(), value,
logger.get())) {
RecordTick(options.statistics.get(), NUMBER_MERGE_FAILURES);
*s = Status::Corruption("Error: Could not perform merge.");
}
} else {
*s = Status::NotFound();
}
found_final_value = true;
break;
}
case kTypeMerge: {
Slice v = GetLengthPrefixedSlice(key_ptr + key_length);
merge_in_progress = true;
merge_context.PushOperand(v);
while(merge_context.GetNumOperands() >= 2) {
// Attempt to associative merge. (Returns true if successful)
if (merge_operator->PartialMerge(key.user_key(),
merge_context.GetOperand(0),
merge_context.GetOperand(1),
&merge_result, logger.get())) {
merge_context.PushPartialMergeResult(merge_result);
} else {
// Stack them because user can't associative merge
break;
}
}
break;
}
default:
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 (!found_final_value && merge_in_progress) {
*s = Status::MergeInProgress("");
}
BumpPerfTime(&perf_context.get_from_memtable_time, &memtable_get_timer);
BumpPerfCount(&perf_context.get_from_memtable_count);
return found_final_value;
}
void MemTable::Update(SequenceNumber seq,
const Slice& key,
const Slice& value) {
LookupKey lkey(key, seq);
Slice mem_key = lkey.memtable_key();
std::unique_ptr<MemTableRep::Iterator> iter(
table_->GetIterator(lkey.user_key()));
iter->Seek(key, mem_key.data());
if (iter->Valid()) {
// entry format is:
// key_length 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: {
Slice prev_value = GetLengthPrefixedSlice(key_ptr + key_length);
uint32_t prev_size = prev_value.size();
uint32_t new_size = value.size();
// Update value, if new value size <= previous value size
if (new_size <= prev_size ) {
char* p = EncodeVarint32(const_cast<char*>(key_ptr) + key_length,
new_size);
WriteLock wl(GetLock(lkey.user_key()));
memcpy(p, value.data(), new_size);
assert(
(p + new_size) - entry ==
(unsigned) (VarintLength(key_length) +
key_length +
VarintLength(new_size) +
new_size)
);
// no need to update bloom, as user key does not change.
return;
}
}
default:
// If the latest value is kTypeDeletion, kTypeMerge or kTypeLogData
// we don't have enough space for update inplace
Add(seq, kTypeValue, key, value);
return;
}
}
}
// key doesn't exist
Add(seq, kTypeValue, key, value);
}
bool MemTable::UpdateCallback(SequenceNumber seq,
const Slice& key,
const Slice& delta,
const Options& options) {
LookupKey lkey(key, seq);
Slice memkey = lkey.memtable_key();
std::shared_ptr<MemTableRep::Iterator> iter(
table_->GetIterator(lkey.user_key()));
iter->Seek(key, memkey.data());
if (iter->Valid()) {
// entry format is:
// key_length 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: {
Slice prev_value = GetLengthPrefixedSlice(key_ptr + key_length);
uint32_t prev_size = prev_value.size();
char* prev_buffer = const_cast<char*>(prev_value.data());
uint32_t new_prev_size = prev_size;
std::string str_value;
WriteLock wl(GetLock(lkey.user_key()));
auto status = options.inplace_callback(prev_buffer, &new_prev_size,
delta, &str_value);
if (status == UpdateStatus::UPDATED_INPLACE) {
// Value already updated by callback.
assert(new_prev_size <= prev_size);
if (new_prev_size < prev_size) {
// overwrite the new prev_size
char* p = EncodeVarint32(const_cast<char*>(key_ptr) + key_length,
new_prev_size);
if (VarintLength(new_prev_size) < VarintLength(prev_size)) {
// shift the value buffer as well.
memcpy(p, prev_buffer, new_prev_size);
}
}
RecordTick(options.statistics.get(), NUMBER_KEYS_UPDATED);
return true;
} else if (status == UpdateStatus::UPDATED) {
Add(seq, kTypeValue, key, Slice(str_value));
RecordTick(options.statistics.get(), NUMBER_KEYS_WRITTEN);
return true;
} else if (status == UpdateStatus::UPDATE_FAILED) {
// No action required. Return.
return true;
}
}
default:
break;
}
}
}
// If the latest value is not kTypeValue
// or key doesn't exist
return false;
}
size_t MemTable::CountSuccessiveMergeEntries(const LookupKey& key) {
Slice memkey = key.memtable_key();
// A total ordered iterator is costly for some memtablerep (prefix aware
// reps). By passing in the user key, we allow efficient iterator creation.
// The iterator only needs to be ordered within the same user key.
std::unique_ptr<MemTableRep::Iterator> iter(
table_->GetIterator(key.user_key()));
iter->Seek(key.user_key(), memkey.data());
size_t num_successive_merges = 0;
for (; iter->Valid(); iter->Next()) {
const char* entry = iter->key();
uint32_t key_length;
const char* iter_key_ptr = GetVarint32Ptr(entry, entry + 5, &key_length);
if (!comparator_.comparator.user_comparator()->Compare(
Slice(iter_key_ptr, key_length - 8), key.user_key()) == 0) {
break;
}
const uint64_t tag = DecodeFixed64(iter_key_ptr + key_length - 8);
if (static_cast<ValueType>(tag & 0xff) != kTypeMerge) {
break;
}
++num_successive_merges;
}
return num_successive_merges;
}
} // namespace rocksdb
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