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leveldb_ttl
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leveldb_ttl/db/version_set.cc

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// 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/version_set.h"
#include <algorithm>
#include <cstdio>
#include "db/filename.h"
#include "db/log_reader.h"
#include "db/log_writer.h"
#include "db/memtable.h"
#include "db/table_cache.h"
#include "leveldb/env.h"
#include "leveldb/table_builder.h"
#include "table/merger.h"
#include "table/two_level_iterator.h"
#include "util/coding.h"
#include "util/logging.h"
namespace leveldb {
static size_t TargetFileSize(const Options* options) {
return options->max_file_size;
}
// Maximum bytes of overlaps in grandparent (i.e., level+2) before we
// stop building a single file in a level->level+1 compaction.
static int64_t MaxGrandParentOverlapBytes(const Options* options) {
return 10 * TargetFileSize(options);
}
// Maximum number of bytes in all compacted files. We avoid expanding
// the lower level file set of a compaction if it would make the
// total compaction cover more than this many bytes.
static int64_t ExpandedCompactionByteSizeLimit(const Options* options) {
return 25 * TargetFileSize(options);
}
static double MaxBytesForLevel(const Options* options, int level) {
// Note: the result for level zero is not really used since we set
// the level-0 compaction threshold based on number of files.
// Result for both level-0 and level-1
double result = 10. * 1048576.0;
while (level > 1) {
result *= 10;
level--;
}
return result;
}
static uint64_t MaxFileSizeForLevel(const Options* options, int level) {
// We could vary per level to reduce number of files?
return TargetFileSize(options);
}
static int64_t TotalFileSize(const std::vector<FileMetaData*>& files) {
int64_t sum = 0;
for (size_t i = 0; i < files.size(); i++) {
sum += files[i]->file_size;
}
return sum;
}
Version::~Version() {
assert(refs_ == 0);
// Remove from linked list
prev_->next_ = next_;
next_->prev_ = prev_;
// Drop references to files
for (int level = 0; level < config::kNumLevels; level++) {
for (size_t i = 0; i < files_[level].size(); i++) {
FileMetaData* f = files_[level][i];
assert(f->refs > 0);
f->refs--;
if (f->refs <= 0) {
delete f;
}
}
}
}
//寻找文件的时候也要考虑生存期
int FindFile(const InternalKeyComparator& icmp,
const std::vector<FileMetaData*>& files, const Slice& key) {
uint32_t left = 0;
uint32_t right = files.size();
ParsedInternalKey parsed;
ParseInternalKey(key,&parsed);
while (left < right) {
uint32_t mid = (left + right) / 2;
const FileMetaData* f = files[mid];
if (icmp.InternalKeyComparator::Compare(f->largest.Encode(), key) < 0) {
// Key at "mid.largest" is < "target". Therefore all
// files at or before "mid" are uninteresting.
left = mid + 1;
} else {
// Key at "mid.largest" is >= "target". Therefore all files
// after "mid" are uninteresting.
right = mid;
}
}
while(right < files.size()) {
printf("file ind %d num %lu largest deadtime %lu parsed deadtime %lu\n",
right,files[right]->number,files[right]->largest_deadtime,parsed.deadTime);
if(files[right]->largest_deadtime >= parsed.deadTime) {
break;
}
// if(icmp.InternalKeyComparator::Compare(files[right]->largest.Encode(), key) > 0) {
// break;
// }
right ++;
}
return right;
}
static bool AfterFile(const Comparator* ucmp, const Slice* user_key,
const FileMetaData* f) {
// null user_key occurs before all keys and is therefore never after *f
return (user_key != nullptr &&
ucmp->Compare(*user_key, f->largest.user_key()) > 0);
}
static bool BeforeFile(const Comparator* ucmp, const Slice* user_key,
const FileMetaData* f) {
// null user_key occurs after all keys and is therefore never before *f
return (user_key != nullptr &&
ucmp->Compare(*user_key, f->smallest.user_key()) < 0);
}
bool SomeFileOverlapsRange(const InternalKeyComparator& icmp,
bool disjoint_sorted_files,
const std::vector<FileMetaData*>& files,
const Slice* smallest_user_key,
const Slice* largest_user_key) {
const Comparator* ucmp = icmp.user_comparator();
if (!disjoint_sorted_files) {
// Need to check against all files
for (size_t i = 0; i < files.size(); i++) {
const FileMetaData* f = files[i];
if (AfterFile(ucmp, smallest_user_key, f) ||
BeforeFile(ucmp, largest_user_key, f)) {
// No overlap
} else {
return true; // Overlap
}
}
return false;
}
// Binary search over file list
uint32_t index = 0;
if (smallest_user_key != nullptr) {
// Find the earliest possible internal key for smallest_user_key
InternalKey small_key(*smallest_user_key, kMaxSequenceNumber,
kValueTypeForSeek);
index = FindFile(icmp, files, small_key.Encode());
}
if (index >= files.size()) {
// beginning of range is after all files, so no overlap.
return false;
}
return !BeforeFile(ucmp, largest_user_key, files[index]);
}
// An internal iterator. For a given version/level pair, yields
// information about the files in the level. For a given entry, key()
// is the largest key that occurs in the file, and value() is an
// 16-byte value containing the file number and file size, both
// encoded using EncodeFixed64.
class Version::LevelFileNumIterator : public Iterator {
public:
LevelFileNumIterator(const InternalKeyComparator& icmp,
const std::vector<FileMetaData*>* flist)
: icmp_(icmp), flist_(flist), index_(flist->size()) { // Marks as invalid
}
bool Valid() const override { return index_ < flist_->size(); }
void Seek(const Slice& target) override {
index_ = FindFile(icmp_, *flist_, target);
}
void SeekToFirst() override { index_ = 0; }
void SeekToLast() override {
index_ = flist_->empty() ? 0 : flist_->size() - 1;
}
void Next() override {
assert(Valid());
index_++;
}
void Prev() override {
assert(Valid());
if (index_ == 0) {
index_ = flist_->size(); // Marks as invalid
} else {
index_--;
}
}
Slice key() const override {
assert(Valid());
return (*flist_)[index_]->largest.Encode();
}
Slice value() const override {
assert(Valid());
EncodeFixed64(value_buf_, (*flist_)[index_]->number);
EncodeFixed64(value_buf_ + 8, (*flist_)[index_]->file_size);
return Slice(value_buf_, sizeof(value_buf_));
}
Status status() const override { return Status::OK(); }
private:
const InternalKeyComparator icmp_;
const std::vector<FileMetaData*>* const flist_;
uint32_t index_;
// Backing store for value(). Holds the file number and size.
mutable char value_buf_[16];
};
static Iterator* GetFileIterator(void* arg, const ReadOptions& options,
const Slice& file_value) {
TableCache* cache = reinterpret_cast<TableCache*>(arg);
if (file_value.size() != 16) {
return NewErrorIterator(
Status::Corruption("FileReader invoked with unexpected value"));
} else {
return cache->NewIterator(options, DecodeFixed64(file_value.data()),
DecodeFixed64(file_value.data() + 8));
}
}
Iterator* Version::NewConcatenatingIterator(const ReadOptions& options,
int level) const {
return NewTwoLevelIterator(
new LevelFileNumIterator(vset_->icmp_, &files_[level]), &GetFileIterator,
vset_->table_cache_, options);
}
void Version::AddIterators(const ReadOptions& options,
std::vector<Iterator*>* iters) {
// Merge all level zero files together since they may overlap
for (size_t i = 0; i < files_[0].size(); i++) {
iters->push_back(vset_->table_cache_->NewIterator(
options, files_[0][i]->number, files_[0][i]->file_size));
}
// For levels > 0, we can use a concatenating iterator that sequentially
// walks through the non-overlapping files in the level, opening them
// lazily.
for (int level = 1; level < config::kNumLevels; level++) {
if (!files_[level].empty()) {
iters->push_back(NewConcatenatingIterator(options, level));
}
}
}
// Callback from TableCache::Get()
namespace {
enum SaverState {
kNotFound,
kFound,
kDeleted,
kCorrupt,
};
struct Saver {
SaverState state;
const Comparator* ucmp;
Slice user_key;
std::string* value;
};
} // namespace
static void SaveValue(void* arg, const Slice& ikey, const Slice& v) {
Saver* s = reinterpret_cast<Saver*>(arg);
ParsedInternalKey parsed_key;
if (!ParseInternalKey(ikey, &parsed_key)) {
// std::cout<<"corrupt get"<<std::endl;
s->state = kCorrupt;
} else {
std::cout<<"found & target "<<parsed_key.user_key.ToString()<<" "<<s->user_key.ToString()<<std::endl;
if (s->ucmp->Compare(parsed_key.user_key, s->user_key) == 0) {
s->state = (parsed_key.type == kTypeValue) ? kFound : kDeleted;
if (s->state == kFound) {
s->value->assign(v.data(), v.size());
}
}
}
std::cout<<"state : "<<s->state<<std::endl;
}
static bool NewestFirst(FileMetaData* a, FileMetaData* b) {
return a->number > b->number;
}
void Version::ForEachOverlapping(Slice user_key, Slice internal_key, void* arg,
bool (*func)(void*, int, FileMetaData*)) {
const Comparator* ucmp = vset_->icmp_.user_comparator();
ParsedInternalKey parsed;
ParseInternalKey(internal_key,&parsed);
printf("parsed lookup deadtime : %lu\n",parsed.deadTime);
// Search level-0 in order from newest to oldest.
std::vector<FileMetaData*> tmp;
tmp.reserve(files_[0].size());
for (uint32_t i = 0; i < files_[0].size(); i++) {
FileMetaData* f = files_[0][i];
//除了key的范围之外，还要考虑文件含有kv的最大deadtime
if (ucmp->Compare(user_key, f->smallest.user_key()) >= 0 &&
ucmp->Compare(user_key, f->largest.user_key()) <= 0 &&
f->largest_deadtime > parsed.deadTime) {
tmp.push_back(f);
}
}
if (!tmp.empty()) {
std::sort(tmp.begin(), tmp.end(), NewestFirst);
for (uint32_t i = 0; i < tmp.size(); i++) {
if (!(*func)(arg, 0, tmp[i])) {
return;
}
}
}
// Search other levels.
for (int level = 1; level < config::kNumLevels; level++) {
std::cout<<"----------search in level "<<level<<"--------------\n";
size_t num_files = files_[level].size();
if (num_files == 0) continue;
// Binary search to find earliest index whose largest key >= internal_key.
uint32_t index = FindFile(vset_->icmp_, files_[level], internal_key);
if (index < num_files) {
FileMetaData* f = files_[level][index];
std::cout<<"userkey fsmallest "<<user_key.ToString()<<" "<<f->smallest.user_key().ToString()<<std::endl;
if (ucmp->Compare(user_key, f->smallest.user_key()) < 0) {
// All of "f" is past any data for user_key
} else {
if (!(*func)(arg, level, f)) {
return;
}
}
}
}
}
Status Version::Get(const ReadOptions& options, const LookupKey& k,
std::string* value, GetStats* stats) {
stats->seek_file = nullptr;
stats->seek_file_level = -1;
struct State {
Saver saver;
GetStats* stats;
const ReadOptions* options;
Slice ikey;
FileMetaData* last_file_read;
int last_file_read_level;
VersionSet* vset;
Status s;
bool found;
static bool Match(void* arg, int level, FileMetaData* f) {
State* state = reinterpret_cast<State*>(arg);
if (state->stats->seek_file == nullptr &&
state->last_file_read != nullptr) {
// We have had more than one seek for this read. Charge the 1st file.
state->stats->seek_file = state->last_file_read;
state->stats->seek_file_level = state->last_file_read_level;
}
state->last_file_read = f;
state->last_file_read_level = level;
state->s = state->vset->table_cache_->Get(*state->options, f->number,
f->file_size, state->ikey,
&state->saver, SaveValue);
printf("file level %d num %lu\n", level, f->number);
std::cout<<"state->s ->saver.state: "<<state->s.ok()<<" "<<state->saver.state<<std::endl;
if (!state->s.ok()) {
state->found = true;
return false;
}
switch (state->saver.state) {
case kNotFound:
return true; // Keep searching in other files
case kFound:
state->found = true;
return false;
case kDeleted:
return false;
case kCorrupt:
state->s =
Status::Corruption("corrupted key for ", state->saver.user_key);
state->found = true;
return false;
}
// Not reached. Added to avoid false compilation warnings of
// "control reaches end of non-void function".
return false;
}
};
State state;
state.found = false;
state.stats = stats;
state.last_file_read = nullptr;
state.last_file_read_level = -1;
state.options = &options;
state.ikey = k.internal_key();
state.vset = vset_;
state.saver.state = kNotFound;
state.saver.ucmp = vset_->icmp_.user_comparator();
state.saver.user_key = k.user_key();
state.saver.value = value;
ForEachOverlapping(state.saver.user_key, state.ikey, &state, &State::Match);
return state.found ? state.s : Status::NotFound(Slice());
}
bool Version::UpdateStats(const GetStats& stats) {
FileMetaData* f = stats.seek_file;
if (f != nullptr) {
f->allowed_seeks--;
if (f->allowed_seeks <= 0 && file_to_compact_ == nullptr) {
file_to_compact_ = f;
file_to_compact_level_ = stats.seek_file_level;
return true;
}
}
return false;
}
bool Version::RecordReadSample(Slice internal_key) {
ParsedInternalKey ikey;
if (!ParseInternalKey(internal_key, &ikey)) {
return false;
}
struct State {
GetStats stats; // Holds first matching file
int matches;
static bool Match(void* arg, int level, FileMetaData* f) {
State* state = reinterpret_cast<State*>(arg);
state->matches++;
if (state->matches == 1) {
// Remember first match.
state->stats.seek_file = f;
state->stats.seek_file_level = level;
}
// We can stop iterating once we have a second match.
return state->matches < 2;
}
};
State state;
state.matches = 0;
ForEachOverlapping(ikey.user_key, internal_key, &state, &State::Match);
// Must have at least two matches since we want to merge across
// files. But what if we have a single file that contains many
// overwrites and deletions? Should we have another mechanism for
// finding such files?
if (state.matches >= 2) {
// 1MB cost is about 1 seek (see comment in Builder::Apply).
return UpdateStats(state.stats);
}
return false;
}
void Version::Ref() { ++refs_; }
void Version::Unref() {
assert(this != &vset_->dummy_versions_);
assert(refs_ >= 1);
--refs_;
if (refs_ == 0) {
delete this;
}
}
bool Version::OverlapInLevel(int level, const Slice* smallest_user_key,
const Slice* largest_user_key) {
return SomeFileOverlapsRange(vset_->icmp_, (level > 0), files_[level],
smallest_user_key, largest_user_key);
}
int Version::PickLevelForMemTableOutput(const Slice& smallest_user_key,
const Slice& largest_user_key) {
int level = 0;
if (!OverlapInLevel(0, &smallest_user_key, &largest_user_key)) {
// Push to next level if there is no overlap in next level,
// and the #bytes overlapping in the level after that are limited.
InternalKey start(smallest_user_key, kMaxSequenceNumber, kValueTypeForSeek);
InternalKey limit(largest_user_key, 0, static_cast<ValueType>(0));
std::vector<FileMetaData*> overlaps;
while (level < config::kMaxMemCompactLevel) {
if (OverlapInLevel(level + 1, &smallest_user_key, &largest_user_key)) {
break;
}
if (level + 2 < config::kNumLevels) {
// Check that file does not overlap too many grandparent bytes.
GetOverlappingInputs(level + 2, &start, &limit, &overlaps);
const int64_t sum = TotalFileSize(overlaps);
if (sum > MaxGrandParentOverlapBytes(vset_->options_)) {
break;
}
}
level++;
}
}
return level;
}
// Store in "*inputs" all files in "level" that overlap [begin,end]
void Version::GetOverlappingInputs(int level, const InternalKey* begin,
const InternalKey* end,
std::vector<FileMetaData*>* inputs) {
assert(level >= 0);
assert(level < config::kNumLevels);
inputs->clear();
Slice user_begin, user_end;
if (begin != nullptr) {
user_begin = begin->user_key();
}
if (end != nullptr) {
user_end = end->user_key();
}
const Comparator* user_cmp = vset_->icmp_.user_comparator();
for (size_t i = 0; i < files_[level].size();) {
FileMetaData* f = files_[level][i++];
const Slice file_start = f->smallest.user_key();
const Slice file_limit = f->largest.user_key();
if (begin != nullptr && user_cmp->Compare(file_limit, user_begin) < 0) {
// "f" is completely before specified range; skip it
} else if (end != nullptr && user_cmp->Compare(file_start, user_end) > 0) {
// "f" is completely after specified range; skip it
} else {
inputs->push_back(f);
if (level == 0) {
// Level-0 files may overlap each other. So check if the newly
// added file has expanded the range. If so, restart search.
if (begin != nullptr && user_cmp->Compare(file_start, user_begin) < 0) {
user_begin = file_start;
inputs->clear();
i = 0;
} else if (end != nullptr &&
user_cmp->Compare(file_limit, user_end) > 0) {
user_end = file_limit;
inputs->clear();
i = 0;
}
}
}
}
}
std::string Version::DebugString() const {
std::string r;
for (int level = 0; level < config::kNumLevels; level++) {
// E.g.,
// --- level 1 ---
// 17:123['a' .. 'd']
// 20:43['e' .. 'g']
r.append("--- level ");
AppendNumberTo(&r, level);
r.append(" ---\n");
const std::vector<FileMetaData*>& files = files_[level];
for (size_t i = 0; i < files.size(); i++) {
r.push_back(' ');
AppendNumberTo(&r, files[i]->number);
r.push_back(':');
AppendNumberTo(&r, files[i]->file_size);
r.append("[");
r.append(files[i]->smallest.DebugString());
r.append(" .. ");
r.append(files[i]->largest.DebugString());
r.append("]\n");
}
}
return r;
}
// A helper class so we can efficiently apply a whole sequence
// of edits to a particular state without creating intermediate
// Versions that contain full copies of the intermediate state.
class VersionSet::Builder {
private:
// Helper to sort by v->files_[file_number].smallest
struct BySmallestKey {
const InternalKeyComparator* internal_comparator;
bool operator()(FileMetaData* f1, FileMetaData* f2) const {
int r = internal_comparator->Compare(f1->smallest, f2->smallest);
if (r != 0) {
return (r < 0);
} else {
// Break ties by file number
return (f1->number < f2->number);
}
}
};
typedef std::set<FileMetaData*, BySmallestKey> FileSet;
struct LevelState {
std::set<uint64_t> deleted_files;
FileSet* added_files;
};
VersionSet* vset_;
Version* base_;
LevelState levels_[config::kNumLevels];
public:
// Initialize a builder with the files from *base and other info from *vset
Builder(VersionSet* vset, Version* base) : vset_(vset), base_(base) {
base_->Ref();
BySmallestKey cmp;
cmp.internal_comparator = &vset_->icmp_;
for (int level = 0; level < config::kNumLevels; level++) {
levels_[level].added_files = new FileSet(cmp);
}
}
~Builder() {
for (int level = 0; level < config::kNumLevels; level++) {
const FileSet* added = levels_[level].added_files;
std::vector<FileMetaData*> to_unref;
to_unref.reserve(added->size());
for (FileSet::const_iterator it = added->begin(); it != added->end();
++it) {
to_unref.push_back(*it);
}
delete added;
for (uint32_t i = 0; i < to_unref.size(); i++) {
FileMetaData* f = to_unref[i];
f->refs--;
if (f->refs <= 0) {
delete f;
}
}
}
base_->Unref();
}
// Apply all of the edits in *edit to the current state.
void Apply(const VersionEdit* edit) {
// Update compaction pointers
for (size_t i = 0; i < edit->compact_pointers_.size(); i++) {
const int level = edit->compact_pointers_[i].first;
vset_->compact_pointer_[level] =
edit->compact_pointers_[i].second.Encode().ToString();
}
// Delete files
for (const auto& deleted_file_set_kvp : edit->deleted_files_) {
const int level = deleted_file_set_kvp.first;
const uint64_t number = deleted_file_set_kvp.second;
levels_[level].deleted_files.insert(number);
}
// Add new files
for (size_t i = 0; i < edit->new_files_.size(); i++) {
const int level = edit->new_files_[i].first;
FileMetaData* f = new FileMetaData(edit->new_files_[i].second);
f->refs = 1;
// We arrange to automatically compact this file after
// a certain number of seeks. Let's assume:
// (1) One seek costs 10ms
// (2) Writing or reading 1MB costs 10ms (100MB/s)
// (3) A compaction of 1MB does 25MB of IO:
// 1MB read from this level
// 10-12MB read from next level (boundaries may be misaligned)
// 10-12MB written to next level
// This implies that 25 seeks cost the same as the compaction
// of 1MB of data. I.e., one seek costs approximately the
// same as the compaction of 40KB of data. We are a little
// conservative and allow approximately one seek for every 16KB
// of data before triggering a compaction.
f->allowed_seeks = static_cast<int>((f->file_size / 16384U));
if (f->allowed_seeks < 100) f->allowed_seeks = 100;
levels_[level].deleted_files.erase(f->number);
levels_[level].added_files->insert(f);
}
}
// Save the current state in *v.
void SaveTo(Version* v) {
BySmallestKey cmp;
cmp.internal_comparator = &vset_->icmp_;
for (int level = 0; level < config::kNumLevels; level++) {
// Merge the set of added files with the set of pre-existing files.
// Drop any deleted files. Store the result in *v.
const std::vector<FileMetaData*>& base_files = base_->files_[level];
std::vector<FileMetaData*>::const_iterator base_iter = base_files.begin();
std::vector<FileMetaData*>::const_iterator base_end = base_files.end();
const FileSet* added_files = levels_[level].added_files;
v->files_[level].reserve(base_files.size() + added_files->size());
for (const auto& added_file : *added_files) {
// Add all smaller files listed in base_
for (std::vector<FileMetaData*>::const_iterator bpos =
std::upper_bound(base_iter, base_end, added_file, cmp);
base_iter != bpos; ++base_iter) {
MaybeAddFile(v, level, *base_iter);
}
MaybeAddFile(v, level, added_file);
}
// Add remaining base files
for (; base_iter != base_end; ++base_iter) {
MaybeAddFile(v, level, *base_iter);
}
#ifndef NDEBUG
// Make sure there is no overlap in levels > 0
if (level > 0) {
for (uint32_t i = 1; i < v->files_[level].size(); i++) {
const InternalKey& prev_end = v->files_[level][i - 1]->largest;
const InternalKey& this_begin = v->files_[level][i]->smallest;
if (vset_->icmp_.Compare(prev_end, this_begin) >= 0) {
std::fprintf(stderr, "overlapping ranges in same level %s vs. %s\n",
prev_end.DebugString().c_str(),
this_begin.DebugString().c_str());
std::abort();
}
}
}
#endif
}
}
void MaybeAddFile(Version* v, int level, FileMetaData* f) {
if (levels_[level].deleted_files.count(f->number) > 0) {
// File is deleted: do nothing
} else {
std::vector<FileMetaData*>* files = &v->files_[level];
if (level > 0 && !files->empty()) {
// Must not overlap
assert(vset_->icmp_.Compare((*files)[files->size() - 1]->largest,
f->smallest) < 0);
}
f->refs++;
files->push_back(f);
}
}
};
VersionSet::VersionSet(const std::string& dbname, const Options* options,
TableCache* table_cache,
const InternalKeyComparator* cmp)
: env_(options->env),
dbname_(dbname),
options_(options),
table_cache_(table_cache),
icmp_(*cmp),
next_file_number_(2),
manifest_file_number_(0), // Filled by Recover()
last_sequence_(0),
log_number_(0),
prev_log_number_(0),
descriptor_file_(nullptr),
descriptor_log_(nullptr),
dummy_versions_(this),
current_(nullptr) {
AppendVersion(new Version(this));
}
VersionSet::~VersionSet() {
current_->Unref();
assert(dummy_versions_.next_ == &dummy_versions_); // List must be empty
delete descriptor_log_;
delete descriptor_file_;
}
void VersionSet::AppendVersion(Version* v) {
// Make "v" current
assert(v->refs_ == 0);
assert(v != current_);
if (current_ != nullptr) {
current_->Unref();
}
current_ = v;
v->Ref();
// Append to linked list
v->prev_ = dummy_versions_.prev_;
v->next_ = &dummy_versions_;
v->prev_->next_ = v;
v->next_->prev_ = v;
}
Status VersionSet::LogAndApply(VersionEdit* edit, port::Mutex* mu) {
if (edit->has_log_number_) {
assert(edit->log_number_ >= log_number_);
assert(edit->log_number_ < next_file_number_);
} else {
edit->SetLogNumber(log_number_);
}
if (!edit->has_prev_log_number_) {
edit->SetPrevLogNumber(prev_log_number_);
}
edit->SetNextFile(next_file_number_);
edit->SetLastSequence(last_sequence_);
Version* v = new Version(this);
{
Builder builder(this, current_);
builder.Apply(edit);
builder.SaveTo(v);
}
Finalize(v);
// Initialize new descriptor log file if necessary by creating
// a temporary file that contains a snapshot of the current version.
std::string new_manifest_file;
Status s;
if (descriptor_log_ == nullptr) {
// No reason to unlock *mu here since we only hit this path in the
// first call to LogAndApply (when opening the database).
assert(descriptor_file_ == nullptr);
new_manifest_file = DescriptorFileName(dbname_, manifest_file_number_);
s = env_->NewWritableFile(new_manifest_file, &descriptor_file_);
if (s.ok()) {
descriptor_log_ = new log::Writer(descriptor_file_);
s = WriteSnapshot(descriptor_log_);
}
}
// Unlock during expensive MANIFEST log write
{
mu->Unlock();
// Write new record to MANIFEST log
if (s.ok()) {
std::string record;
edit->EncodeTo(&record);
s = descriptor_log_->AddRecord(record);
if (s.ok()) {
s = descriptor_file_->Sync();
}
if (!s.ok()) {
Log(options_->info_log, "MANIFEST write: %s\n", s.ToString().c_str());
}
}
// If we just created a new descriptor file, install it by writing a
// new CURRENT file that points to it.
if (s.ok() && !new_manifest_file.empty()) {
s = SetCurrentFile(env_, dbname_, manifest_file_number_);
}
mu->Lock();
}
// Install the new version
if (s.ok()) {
AppendVersion(v);
log_number_ = edit->log_number_;
prev_log_number_ = edit->prev_log_number_;
} else {
delete v;
if (!new_manifest_file.empty()) {
delete descriptor_log_;
delete descriptor_file_;
descriptor_log_ = nullptr;
descriptor_file_ = nullptr;
env_->RemoveFile(new_manifest_file);
}
}
return s;
}
Status VersionSet::Recover(bool* save_manifest) {
struct LogReporter : public log::Reader::Reporter {
Status* status;
void Corruption(size_t bytes, const Status& s) override {
if (this->status->ok()) *this->status = s;
}
};
// Read "CURRENT" file, which contains a pointer to the current manifest file
std::string current;
Status s = ReadFileToString(env_, CurrentFileName(dbname_), &current);
if (!s.ok()) {
return s;
}
if (current.empty() || current[current.size() - 1] != '\n') {
return Status::Corruption("CURRENT file does not end with newline");
}
current.resize(current.size() - 1);
std::string dscname = dbname_ + "/" + current;
SequentialFile* file;
s = env_->NewSequentialFile(dscname, &file);
if (!s.ok()) {
if (s.IsNotFound()) {
return Status::Corruption("CURRENT points to a non-existent file",
s.ToString());
}
return s;
}
bool have_log_number = false;
bool have_prev_log_number = false;
bool have_next_file = false;
bool have_last_sequence = false;
uint64_t next_file = 0;
uint64_t last_sequence = 0;
uint64_t log_number = 0;
uint64_t prev_log_number = 0;
Builder builder(this, current_);
int read_records = 0;
{
LogReporter reporter;
reporter.status = &s;
log::Reader reader(file, &reporter, true /*checksum*/,
0 /*initial_offset*/);
Slice record;
std::string scratch;
while (reader.ReadRecord(&record, &scratch) && s.ok()) {
++read_records;
VersionEdit edit;
s = edit.DecodeFrom(record);
if (s.ok()) {
if (edit.has_comparator_ &&
edit.comparator_ != icmp_.user_comparator()->Name()) {
s = Status::InvalidArgument(
edit.comparator_ + " does not match existing comparator ",
icmp_.user_comparator()->Name());
}
}
if (s.ok()) {
builder.Apply(&edit);
}
if (edit.has_log_number_) {
log_number = edit.log_number_;
have_log_number = true;
}
if (edit.has_prev_log_number_) {
prev_log_number = edit.prev_log_number_;
have_prev_log_number = true;
}
if (edit.has_next_file_number_) {
next_file = edit.next_file_number_;
have_next_file = true;
}
if (edit.has_last_sequence_) {
last_sequence = edit.last_sequence_;
have_last_sequence = true;
}
}
}
delete file;
file = nullptr;
if (s.ok()) {
if (!have_next_file) {
s = Status::Corruption("no meta-nextfile entry in descriptor");
} else if (!have_log_number) {
s = Status::Corruption("no meta-lognumber entry in descriptor");
} else if (!have_last_sequence) {
s = Status::Corruption("no last-sequence-number entry in descriptor");
}
if (!have_prev_log_number) {
prev_log_number = 0;
}
MarkFileNumberUsed(prev_log_number);
MarkFileNumberUsed(log_number);
}
if (s.ok()) {
Version* v = new Version(this);
builder.SaveTo(v);
// Install recovered version
Finalize(v);
AppendVersion(v);
manifest_file_number_ = next_file;
next_file_number_ = next_file + 1;
last_sequence_ = last_sequence;
log_number_ = log_number;
prev_log_number_ = prev_log_number;
// See if we can reuse the existing MANIFEST file.
if (ReuseManifest(dscname, current)) {
// No need to save new manifest
} else {
*save_manifest = true;
}
} else {
std::string error = s.ToString();
Log(options_->info_log, "Error recovering version set with %d records: %s",
read_records, error.c_str());
}
return s;
}
bool VersionSet::ReuseManifest(const std::string& dscname,
const std::string& dscbase) {
if (!options_->reuse_logs) {
return false;
}
FileType manifest_type;
uint64_t manifest_number;
uint64_t manifest_size;
if (!ParseFileName(dscbase, &manifest_number, &manifest_type) ||
manifest_type != kDescriptorFile ||
!env_->GetFileSize(dscname, &manifest_size).ok() ||
// Make new compacted MANIFEST if old one is too big
manifest_size >= TargetFileSize(options_)) {
return false;
}
assert(descriptor_file_ == nullptr);
assert(descriptor_log_ == nullptr);
Status r = env_->NewAppendableFile(dscname, &descriptor_file_);
if (!r.ok()) {
Log(options_->info_log, "Reuse MANIFEST: %s\n", r.ToString().c_str());
assert(descriptor_file_ == nullptr);
return false;
}
Log(options_->info_log, "Reusing MANIFEST %s\n", dscname.c_str());
descriptor_log_ = new log::Writer(descriptor_file_, manifest_size);
manifest_file_number_ = manifest_number;
return true;
}
void VersionSet::MarkFileNumberUsed(uint64_t number) {
if (next_file_number_ <= number) {
next_file_number_ = number + 1;
}
}
void VersionSet::Finalize(Version* v) {
// Precomputed best level for next compaction
int best_level = -1;
double best_score = -1;
for (int level = 0; level < config::kNumLevels - 1; level++) {
double score;
if (level == 0) {
// We treat level-0 specially by bounding the number of files
// instead of number of bytes for two reasons:
//
// (1) With larger write-buffer sizes, it is nice not to do too
// many level-0 compactions.
//
// (2) The files in level-0 are merged on every read and
// therefore we wish to avoid too many files when the individual
// file size is small (perhaps because of a small write-buffer
// setting, or very high compression ratios, or lots of
// overwrites/deletions).
score = v->files_[level].size() /
static_cast<double>(config::kL0_CompactionTrigger);
} else {
// Compute the ratio of current size to size limit.
const uint64_t level_bytes = TotalFileSize(v->files_[level]);
score =
static_cast<double>(level_bytes) / MaxBytesForLevel(options_, level);
}
if (score > best_score) {
best_level = level;
best_score = score;
}
}
v->compaction_level_ = best_level;
v->compaction_score_ = best_score;
}
Status VersionSet::WriteSnapshot(log::Writer* log) {
// TODO: Break up into multiple records to reduce memory usage on recovery?
// Save metadata
VersionEdit edit;
edit.SetComparatorName(icmp_.user_comparator()->Name());
// Save compaction pointers
for (int level = 0; level < config::kNumLevels; level++) {
if (!compact_pointer_[level].empty()) {
InternalKey key;
key.DecodeFrom(compact_pointer_[level]);
edit.SetCompactPointer(level, key);
}
}
// Save files
for (int level = 0; level < config::kNumLevels; level++) {
const std::vector<FileMetaData*>& files = current_->files_[level];
for (size_t i = 0; i < files.size(); i++) {
const FileMetaData* f = files[i];
edit.AddFile(level, f->number, f->file_size, f->smallest, f->largest,
f->smallest_deadtime,f->largest_deadtime);
}
}
std::string record;
edit.EncodeTo(&record);
return log->AddRecord(record);
}
int VersionSet::NumLevelFiles(int level) const {
assert(level >= 0);
assert(level < config::kNumLevels);
return current_->files_[level].size();
}
const char* VersionSet::LevelSummary(LevelSummaryStorage* scratch) const {
// Update code if kNumLevels changes
static_assert(config::kNumLevels == 7, "");
std::snprintf(
scratch->buffer, sizeof(scratch->buffer), "files[ %d %d %d %d %d %d %d ]",
int(current_->files_[0].size()), int(current_->files_[1].size()),
int(current_->files_[2].size()), int(current_->files_[3].size()),
int(current_->files_[4].size()), int(current_->files_[5].size()),
int(current_->files_[6].size()));
return scratch->buffer;
}
uint64_t VersionSet::ApproximateOffsetOf(Version* v, const InternalKey& ikey) {
uint64_t result = 0;
for (int level = 0; level < config::kNumLevels; level++) {
const std::vector<FileMetaData*>& files = v->files_[level];
for (size_t i = 0; i < files.size(); i++) {
if (icmp_.Compare(files[i]->largest, ikey) <= 0) {
// Entire file is before "ikey", so just add the file size
result += files[i]->file_size;
} else if (icmp_.Compare(files[i]->smallest, ikey) > 0) {
// Entire file is after "ikey", so ignore
if (level > 0) {
// Files other than level 0 are sorted by meta->smallest, so
// no further files in this level will contain data for
// "ikey".
break;
}
} else {
// "ikey" falls in the range for this table. Add the
// approximate offset of "ikey" within the table.
Table* tableptr;
Iterator* iter = table_cache_->NewIterator(
ReadOptions(), files[i]->number, files[i]->file_size, &tableptr);
if (tableptr != nullptr) {
result += tableptr->ApproximateOffsetOf(ikey.Encode());
}
delete iter;
}
}
}
return result;
}
void VersionSet::AddLiveFiles(std::set<uint64_t>* live) {
for (Version* v = dummy_versions_.next_; v != &dummy_versions_;
v = v->next_) {
for (int level = 0; level < config::kNumLevels; level++) {
const std::vector<FileMetaData*>& files = v->files_[level];
for (size_t i = 0; i < files.size(); i++) {
live->insert(files[i]->number);
}
}
}
}
int64_t VersionSet::NumLevelBytes(int level) const {
assert(level >= 0);
assert(level < config::kNumLevels);
return TotalFileSize(current_->files_[level]);
}
int64_t VersionSet::MaxNextLevelOverlappingBytes() {
int64_t result = 0;
std::vector<FileMetaData*> overlaps;
for (int level = 1; level < config::kNumLevels - 1; level++) {
for (size_t i = 0; i < current_->files_[level].size(); i++) {
const FileMetaData* f = current_->files_[level][i];
current_->GetOverlappingInputs(level + 1, &f->smallest, &f->largest,
&overlaps);
const int64_t sum = TotalFileSize(overlaps);
if (sum > result) {
result = sum;
}
}
}
return result;
}
// Stores the minimal range that covers all entries in inputs in
// *smallest, *largest.
// REQUIRES: inputs is not empty
void VersionSet::GetRange(const std::vector<FileMetaData*>& inputs,
InternalKey* smallest, InternalKey* largest) {
assert(!inputs.empty());
smallest->Clear();
largest->Clear();
for (size_t i = 0; i < inputs.size(); i++) {
FileMetaData* f = inputs[i];
if (i == 0) {
*smallest = f->smallest;
*largest = f->largest;
} else {
if (icmp_.Compare(f->smallest, *smallest) < 0) {
*smallest = f->smallest;
}
if (icmp_.Compare(f->largest, *largest) > 0) {
*largest = f->largest;
}
}
}
}
// Stores the minimal range that covers all entries in inputs1 and inputs2
// in *smallest, *largest.
// REQUIRES: inputs is not empty
void VersionSet::GetRange2(const std::vector<FileMetaData*>& inputs1,
const std::vector<FileMetaData*>& inputs2,
InternalKey* smallest, InternalKey* largest) {
std::vector<FileMetaData*> all = inputs1;
all.insert(all.end(), inputs2.begin(), inputs2.end());
GetRange(all, smallest, largest);
}
Iterator* VersionSet::MakeInputIterator(Compaction* c) {
ReadOptions options;
options.verify_checksums = options_->paranoid_checks;
options.fill_cache = false;
// Level-0 files have to be merged together. For other levels,
// we will make a concatenating iterator per level.
// TODO(opt): use concatenating iterator for level-0 if there is no overlap
const int space = (c->level() == 0 ? c->inputs_[0].size() + 1 : 2);
Iterator** list = new Iterator*[space];
int num = 0;
for (int which = 0; which < 2; which++) {
if (!c->inputs_[which].empty()) {
if (c->level() + which == 0) {
const std::vector<FileMetaData*>& files = c->inputs_[which];
for (size_t i = 0; i < files.size(); i++) {
list[num++] = table_cache_->NewIterator(options, files[i]->number,
files[i]->file_size);
}
} else {
// Create concatenating iterator for the files from this level
list[num++] = NewTwoLevelIterator(
new Version::LevelFileNumIterator(icmp_, &c->inputs_[which]),
&GetFileIterator, table_cache_, options);
}
}
}
assert(num <= space);
Iterator* result = NewMergingIterator(&icmp_, list, num);
delete[] list;
return result;
}
Compaction* VersionSet::PickCompaction() {
Compaction* c;
int level;
// We prefer compactions triggered by too much data in a level over
// the compactions triggered by seeks.
const bool size_compaction = (current_->compaction_score_ >= 1);
const bool seek_compaction = (current_->file_to_compact_ != nullptr);
if (size_compaction) {
level = current_->compaction_level_;
assert(level >= 0);
assert(level + 1 < config::kNumLevels);
c = new Compaction(options_, level);
// Pick the first file that comes after compact_pointer_[level]
for (size_t i = 0; i < current_->files_[level].size(); i++) {
FileMetaData* f = current_->files_[level][i];
if (compact_pointer_[level].empty() ||
icmp_.Compare(f->largest.Encode(), compact_pointer_[level]) > 0) {
c->inputs_[0].push_back(f);
break;
}
}
if (c->inputs_[0].empty()) {
// Wrap-around to the beginning of the key space
c->inputs_[0].push_back(current_->files_[level][0]);
}
} else if (seek_compaction) {
level = current_->file_to_compact_level_;
c = new Compaction(options_, level);
c->inputs_[0].push_back(current_->file_to_compact_);
} else {
return nullptr;
}
c->input_version_ = current_;
c->input_version_->Ref();
// Files in level 0 may overlap each other, so pick up all overlapping ones
if (level == 0) {
InternalKey smallest, largest;
GetRange(c->inputs_[0], &smallest, &largest);
// Note that the next call will discard the file we placed in
// c->inputs_[0] earlier and replace it with an overlapping set
// which will include the picked file.
current_->GetOverlappingInputs(0, &smallest, &largest, &c->inputs_[0]);
assert(!c->inputs_[0].empty());
}
SetupOtherInputs(c);
return c;
}
// Finds the largest key in a vector of files. Returns true if files is not
// empty.
bool FindLargestKey(const InternalKeyComparator& icmp,
const std::vector<FileMetaData*>& files,
InternalKey* largest_key) {
if (files.empty()) {
return false;
}
*largest_key = files[0]->largest;
for (size_t i = 1; i < files.size(); ++i) {
FileMetaData* f = files[i];
if (icmp.Compare(f->largest, *largest_key) > 0) {
*largest_key = f->largest;
}
}
return true;
}
// Finds minimum file b2=(l2, u2) in level file for which l2 > u1 and
// user_key(l2) = user_key(u1)
FileMetaData* FindSmallestBoundaryFile(
const InternalKeyComparator& icmp,
const std::vector<FileMetaData*>& level_files,
const InternalKey& largest_key) {
const Comparator* user_cmp = icmp.user_comparator();
FileMetaData* smallest_boundary_file = nullptr;
for (size_t i = 0; i < level_files.size(); ++i) {
FileMetaData* f = level_files[i];
if (icmp.Compare(f->smallest, largest_key) > 0 &&
user_cmp->Compare(f->smallest.user_key(), largest_key.user_key()) ==
0) {
if (smallest_boundary_file == nullptr ||
icmp.Compare(f->smallest, smallest_boundary_file->smallest) < 0) {
smallest_boundary_file = f;
}
}
}
return smallest_boundary_file;
}
// Extracts the largest file b1 from |compaction_files| and then searches for a
// b2 in |level_files| for which user_key(u1) = user_key(l2). If it finds such a
// file b2 (known as a boundary file) it adds it to |compaction_files| and then
// searches again using this new upper bound.
//
// If there are two blocks, b1=(l1, u1) and b2=(l2, u2) and
// user_key(u1) = user_key(l2), and if we compact b1 but not b2 then a
// subsequent get operation will yield an incorrect result because it will
// return the record from b2 in level i rather than from b1 because it searches
// level by level for records matching the supplied user key.
//
// parameters:
// in level_files: List of files to search for boundary files.
// in/out compaction_files: List of files to extend by adding boundary files.
void AddBoundaryInputs(const InternalKeyComparator& icmp,
const std::vector<FileMetaData*>& level_files,
std::vector<FileMetaData*>* compaction_files) {
InternalKey largest_key;
// Quick return if compaction_files is empty.
if (!FindLargestKey(icmp, *compaction_files, &largest_key)) {
return;
}
bool continue_searching = true;
while (continue_searching) {
FileMetaData* smallest_boundary_file =
FindSmallestBoundaryFile(icmp, level_files, largest_key);
// If a boundary file was found advance largest_key, otherwise we're done.
if (smallest_boundary_file != NULL) {
compaction_files->push_back(smallest_boundary_file);
largest_key = smallest_boundary_file->largest;
} else {
continue_searching = false;
}
}
}
void VersionSet::SetupOtherInputs(Compaction* c) {
const int level = c->level();
InternalKey smallest, largest;
AddBoundaryInputs(icmp_, current_->files_[level], &c->inputs_[0]);
GetRange(c->inputs_[0], &smallest, &largest);
current_->GetOverlappingInputs(level + 1, &smallest, &largest,
&c->inputs_[1]);
AddBoundaryInputs(icmp_, current_->files_[level + 1], &c->inputs_[1]);
// Get entire range covered by compaction
InternalKey all_start, all_limit;
GetRange2(c->inputs_[0], c->inputs_[1], &all_start, &all_limit);
// See if we can grow the number of inputs in "level" without
// changing the number of "level+1" files we pick up.
if (!c->inputs_[1].empty()) {
std::vector<FileMetaData*> expanded0;
current_->GetOverlappingInputs(level, &all_start, &all_limit, &expanded0);
AddBoundaryInputs(icmp_, current_->files_[level], &expanded0);
const int64_t inputs0_size = TotalFileSize(c->inputs_[0]);
const int64_t inputs1_size = TotalFileSize(c->inputs_[1]);
const int64_t expanded0_size = TotalFileSize(expanded0);
if (expanded0.size() > c->inputs_[0].size() &&
inputs1_size + expanded0_size <
ExpandedCompactionByteSizeLimit(options_)) {
InternalKey new_start, new_limit;
GetRange(expanded0, &new_start, &new_limit);
std::vector<FileMetaData*> expanded1;
current_->GetOverlappingInputs(level + 1, &new_start, &new_limit,
&expanded1);
AddBoundaryInputs(icmp_, current_->files_[level + 1], &expanded1);
if (expanded1.size() == c->inputs_[1].size()) {
Log(options_->info_log,
"Expanding@%d %d+%d (%ld+%ld bytes) to %d+%d (%ld+%ld bytes)\n",
level, int(c->inputs_[0].size()), int(c->inputs_[1].size()),
long(inputs0_size), long(inputs1_size), int(expanded0.size()),
int(expanded1.size()), long(expanded0_size), long(inputs1_size));
smallest = new_start;
largest = new_limit;
c->inputs_[0] = expanded0;
c->inputs_[1] = expanded1;
GetRange2(c->inputs_[0], c->inputs_[1], &all_start, &all_limit);
}
}
}
// Compute the set of grandparent files that overlap this compaction
// (parent == level+1; grandparent == level+2)
if (level + 2 < config::kNumLevels) {
current_->GetOverlappingInputs(level + 2, &all_start, &all_limit,
&c->grandparents_);
}
// Update the place where we will do the next compaction for this level.
// We update this immediately instead of waiting for the VersionEdit
// to be applied so that if the compaction fails, we will try a different
// key range next time.
compact_pointer_[level] = largest.Encode().ToString();
c->edit_.SetCompactPointer(level, largest);
}
Compaction* VersionSet::CompactRange(int level, const InternalKey* begin,
const InternalKey* end) {
std::vector<FileMetaData*> inputs;
current_->GetOverlappingInputs(level, begin, end, &inputs);
if (inputs.empty()) {
return nullptr;
}
// Avoid compacting too much in one shot in case the range is large.
// But we cannot do this for level-0 since level-0 files can overlap
// and we must not pick one file and drop another older file if the
// two files overlap.
if (level > 0) {
const uint64_t limit = MaxFileSizeForLevel(options_, level);
uint64_t total = 0;
for (size_t i = 0; i < inputs.size(); i++) {
uint64_t s = inputs[i]->file_size;
total += s;
if (total >= limit) {
inputs.resize(i + 1);
break;
}
}
}
Compaction* c = new Compaction(options_, level);
c->input_version_ = current_;
c->input_version_->Ref();
c->inputs_[0] = inputs;
SetupOtherInputs(c);
return c;
}
Compaction::Compaction(const Options* options, int level)
: level_(level),
max_output_file_size_(MaxFileSizeForLevel(options, level)),
input_version_(nullptr),
grandparent_index_(0),
seen_key_(false),
overlapped_bytes_(0) {
for (int i = 0; i < config::kNumLevels; i++) {
level_ptrs_[i] = 0;
}
}
Compaction::~Compaction() {
if (input_version_ != nullptr) {
input_version_->Unref();
}
}
bool Compaction::IsTrivialMove() const {
const VersionSet* vset = input_version_->vset_;
// Avoid a move if there is lots of overlapping grandparent data.
// Otherwise, the move could create a parent file that will require
// a very expensive merge later on.
return (num_input_files(0) == 1 && num_input_files(1) == 0 &&
TotalFileSize(grandparents_) <=
MaxGrandParentOverlapBytes(vset->options_));
}
void Compaction::AddInputDeletions(VersionEdit* edit) {
for (int which = 0; which < 2; which++) {
for (size_t i = 0; i < inputs_[which].size(); i++) {
edit->RemoveFile(level_ + which, inputs_[which][i]->number);
}
}
}
bool Compaction::IsBaseLevelForKey(const Slice& user_key) {
// Maybe use binary search to find right entry instead of linear search?
const Comparator* user_cmp = input_version_->vset_->icmp_.user_comparator();
for (int lvl = level_ + 2; lvl < config::kNumLevels; lvl++) {
const std::vector<FileMetaData*>& files = input_version_->files_[lvl];
while (level_ptrs_[lvl] < files.size()) {
FileMetaData* f = files[level_ptrs_[lvl]];
if (user_cmp->Compare(user_key, f->largest.user_key()) <= 0) {
// We've advanced far enough
if (user_cmp->Compare(user_key, f->smallest.user_key()) >= 0) {
// Key falls in this file's range, so definitely not base level
return false;
}
break;
}
level_ptrs_[lvl]++;
}
}
return true;
}
bool Compaction::ShouldStopBefore(const Slice& internal_key) {
const VersionSet* vset = input_version_->vset_;
// Scan to find earliest grandparent file that contains key.
const InternalKeyComparator* icmp = &vset->icmp_;
while (grandparent_index_ < grandparents_.size() &&
icmp->Compare(internal_key,
grandparents_[grandparent_index_]->largest.Encode()) >
0) {
if (seen_key_) {
overlapped_bytes_ += grandparents_[grandparent_index_]->file_size;
}
grandparent_index_++;
}
seen_key_ = true;
if (overlapped_bytes_ > MaxGrandParentOverlapBytes(vset->options_)) {
// Too much overlap for current output; start new output
overlapped_bytes_ = 0;
return true;
} else {
return false;
}
}
void Compaction::ReleaseInputs() {
if (input_version_ != nullptr) {
input_version_->Unref();
input_version_ = nullptr;
}
}
} // namespace leveldb