rocksdb/db/version_set.h
Ari Ekmekji 3c37b3cccd Determine boundaries of subcompactions
Summary:
Up to this point, the subcompactions that make up a compaction
job have been divided based on the key range of the L1 files, and each
subcompaction has handled the key range of only one file. However
DBOption.max_subcompactions allows the user to designate how many
subcompactions at most to perform. This patch updates the
CompactionJob::GetSubcompactionBoundaries() to determine these
divisions accordingly based on that option and other input/system factors.

The current approach orders the starting and/or ending keys of certain
compaction input files and then generates a histogram to approximate the
size covered by the key range between each consecutive pair of keys. Then
it groups these ranges into groups so that the sizes are approximately equal
to one another. The approach has also been adapted to work for universal
compaction as well instead of just for level-based compaction as it was before.

These subcompactions are then executed in parallel by locally spawning
threads, one for each. The results are then aggregated and the compaction
completed.

Test Plan: make all && make check

Reviewers: yhchiang, anthony, igor, noetzli, sdong

Reviewed By: sdong

Subscribers: MarkCallaghan, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D43269
2015-09-10 13:50:00 -07:00

751 lines
28 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.
//
// The representation of a DBImpl consists of a set of Versions. The
// newest version is called "current". Older versions may be kept
// around to provide a consistent view to live iterators.
//
// Each Version keeps track of a set of Table files per level. The
// entire set of versions is maintained in a VersionSet.
//
// Version,VersionSet are thread-compatible, but require external
// synchronization on all accesses.
#pragma once
#include <atomic>
#include <deque>
#include <limits>
#include <map>
#include <memory>
#include <set>
#include <utility>
#include <vector>
#include "db/dbformat.h"
#include "db/version_builder.h"
#include "db/version_edit.h"
#include "port/port.h"
#include "db/table_cache.h"
#include "db/compaction.h"
#include "db/compaction_picker.h"
#include "db/column_family.h"
#include "db/log_reader.h"
#include "db/file_indexer.h"
#include "db/write_controller.h"
#include "rocksdb/env.h"
#include "util/instrumented_mutex.h"
namespace rocksdb {
namespace log {
class Writer;
}
class Compaction;
class Iterator;
class LogBuffer;
class LookupKey;
class MemTable;
class Version;
class VersionSet;
class WriteBuffer;
class MergeContext;
class ColumnFamilyData;
class ColumnFamilySet;
class TableCache;
class MergeIteratorBuilder;
// Return the smallest index i such that file_level.files[i]->largest >= key.
// Return file_level.num_files if there is no such file.
// REQUIRES: "file_level.files" contains a sorted list of
// non-overlapping files.
extern int FindFile(const InternalKeyComparator& icmp,
const LevelFilesBrief& file_level, const Slice& key);
// Returns true iff some file in "files" overlaps the user key range
// [*smallest,*largest].
// smallest==nullptr represents a key smaller than all keys in the DB.
// largest==nullptr represents a key largest than all keys in the DB.
// REQUIRES: If disjoint_sorted_files, file_level.files[]
// contains disjoint ranges in sorted order.
extern bool SomeFileOverlapsRange(const InternalKeyComparator& icmp,
bool disjoint_sorted_files,
const LevelFilesBrief& file_level,
const Slice* smallest_user_key,
const Slice* largest_user_key);
// Generate LevelFilesBrief from vector<FdWithKeyRange*>
// Would copy smallest_key and largest_key data to sequential memory
// arena: Arena used to allocate the memory
extern void DoGenerateLevelFilesBrief(LevelFilesBrief* file_level,
const std::vector<FileMetaData*>& files,
Arena* arena);
class VersionStorageInfo {
public:
VersionStorageInfo(const InternalKeyComparator* internal_comparator,
const Comparator* user_comparator, int num_levels,
CompactionStyle compaction_style,
VersionStorageInfo* src_vstorage);
~VersionStorageInfo();
void Reserve(int level, size_t size) { files_[level].reserve(size); }
void AddFile(int level, FileMetaData* f);
void SetFinalized();
// Update num_non_empty_levels_.
void UpdateNumNonEmptyLevels();
void GenerateFileIndexer() {
file_indexer_.UpdateIndex(&arena_, num_non_empty_levels_, files_);
}
// Update the accumulated stats from a file-meta.
void UpdateAccumulatedStats(FileMetaData* file_meta);
void ComputeCompensatedSizes();
// Updates internal structures that keep track of compaction scores
// We use compaction scores to figure out which compaction to do next
// REQUIRES: db_mutex held!!
// TODO find a better way to pass compaction_options_fifo.
void ComputeCompactionScore(
const MutableCFOptions& mutable_cf_options,
const CompactionOptionsFIFO& compaction_options_fifo);
// Estimate est_comp_needed_bytes_
void EstimateCompactionBytesNeeded(
const MutableCFOptions& mutable_cf_options);
// This computes files_marked_for_compaction_ and is called by
// ComputeCompactionScore()
void ComputeFilesMarkedForCompaction();
// Generate level_files_brief_ from files_
void GenerateLevelFilesBrief();
// Sort all files for this version based on their file size and
// record results in files_by_size_. The largest files are listed first.
void UpdateFilesBySize();
void GenerateLevel0NonOverlapping();
bool level0_non_overlapping() const {
return level0_non_overlapping_;
}
int MaxInputLevel() const;
// Returns the maxmimum compaction score for levels 1 to max
double max_compaction_score() const { return max_compaction_score_; }
// See field declaration
int max_compaction_score_level() const { return max_compaction_score_level_; }
// Return level number that has idx'th highest score
int CompactionScoreLevel(int idx) const { return compaction_level_[idx]; }
// Return idx'th highest score
double CompactionScore(int idx) const { return compaction_score_[idx]; }
void GetOverlappingInputs(
int level, const InternalKey* begin, // nullptr means before all keys
const InternalKey* end, // nullptr means after all keys
std::vector<FileMetaData*>* inputs,
int hint_index = -1, // index of overlap file
int* file_index = nullptr); // return index of overlap file
void GetOverlappingInputsBinarySearch(
int level,
const Slice& begin, // nullptr means before all keys
const Slice& end, // nullptr means after all keys
std::vector<FileMetaData*>* inputs,
int hint_index, // index of overlap file
int* file_index); // return index of overlap file
void ExtendOverlappingInputs(
int level,
const Slice& begin, // nullptr means before all keys
const Slice& end, // nullptr means after all keys
std::vector<FileMetaData*>* inputs,
unsigned int index); // start extending from this index
// Returns true iff some file in the specified level overlaps
// some part of [*smallest_user_key,*largest_user_key].
// smallest_user_key==NULL represents a key smaller than all keys in the DB.
// largest_user_key==NULL represents a key largest than all keys in the DB.
bool OverlapInLevel(int level, const Slice* smallest_user_key,
const Slice* largest_user_key);
// Returns true iff the first or last file in inputs contains
// an overlapping user key to the file "just outside" of it (i.e.
// just after the last file, or just before the first file)
// REQUIRES: "*inputs" is a sorted list of non-overlapping files
bool HasOverlappingUserKey(const std::vector<FileMetaData*>* inputs,
int level);
int num_levels() const { return num_levels_; }
// REQUIRES: This version has been saved (see VersionSet::SaveTo)
int num_non_empty_levels() const {
assert(finalized_);
return num_non_empty_levels_;
}
// REQUIRES: This version has been finalized.
// (CalculateBaseBytes() is called)
// This may or may not return number of level files. It is to keep backward
// compatible behavior in universal compaction.
int l0_delay_trigger_count() const { return l0_delay_trigger_count_; }
void set_l0_delay_trigger_count(int v) { l0_delay_trigger_count_ = v; }
// REQUIRES: This version has been saved (see VersionSet::SaveTo)
int NumLevelFiles(int level) const {
assert(finalized_);
return static_cast<int>(files_[level].size());
}
// Return the combined file size of all files at the specified level.
uint64_t NumLevelBytes(int level) const;
// REQUIRES: This version has been saved (see VersionSet::SaveTo)
const std::vector<FileMetaData*>& LevelFiles(int level) const {
return files_[level];
}
const rocksdb::LevelFilesBrief& LevelFilesBrief(int level) const {
assert(level < static_cast<int>(level_files_brief_.size()));
return level_files_brief_[level];
}
// REQUIRES: This version has been saved (see VersionSet::SaveTo)
const std::vector<int>& FilesBySize(int level) const {
assert(finalized_);
return files_by_size_[level];
}
// REQUIRES: This version has been saved (see VersionSet::SaveTo)
// REQUIRES: DB mutex held during access
const autovector<std::pair<int, FileMetaData*>>& FilesMarkedForCompaction()
const {
assert(finalized_);
return files_marked_for_compaction_;
}
int base_level() const { return base_level_; }
// REQUIRES: lock is held
// Set the index that is used to offset into files_by_size_ to find
// the next compaction candidate file.
void SetNextCompactionIndex(int level, int index) {
next_file_to_compact_by_size_[level] = index;
}
// REQUIRES: lock is held
int NextCompactionIndex(int level) const {
return next_file_to_compact_by_size_[level];
}
// REQUIRES: This version has been saved (see VersionSet::SaveTo)
const FileIndexer& file_indexer() const {
assert(finalized_);
return file_indexer_;
}
// Only the first few entries of files_by_size_ are sorted.
// There is no need to sort all the files because it is likely
// that on a running system, we need to look at only the first
// few largest files because a new version is created every few
// seconds/minutes (because of concurrent compactions).
static const size_t kNumberFilesToSort = 50;
// Return a human-readable short (single-line) summary of the number
// of files per level. Uses *scratch as backing store.
struct LevelSummaryStorage {
char buffer[1000];
};
struct FileSummaryStorage {
char buffer[3000];
};
const char* LevelSummary(LevelSummaryStorage* scratch) const;
// Return a human-readable short (single-line) summary of files
// in a specified level. Uses *scratch as backing store.
const char* LevelFileSummary(FileSummaryStorage* scratch, int level) const;
// Return the maximum overlapping data (in bytes) at next level for any
// file at a level >= 1.
int64_t MaxNextLevelOverlappingBytes();
// Return a human readable string that describes this version's contents.
std::string DebugString(bool hex = false) const;
uint64_t GetAverageValueSize() const {
if (accumulated_num_non_deletions_ == 0) {
return 0;
}
assert(accumulated_raw_key_size_ + accumulated_raw_value_size_ > 0);
assert(accumulated_file_size_ > 0);
return accumulated_raw_value_size_ / accumulated_num_non_deletions_ *
accumulated_file_size_ /
(accumulated_raw_key_size_ + accumulated_raw_value_size_);
}
uint64_t GetEstimatedActiveKeys() const;
// re-initializes the index that is used to offset into files_by_size_
// to find the next compaction candidate file.
void ResetNextCompactionIndex(int level) {
next_file_to_compact_by_size_[level] = 0;
}
const InternalKeyComparator* InternalComparator() {
return internal_comparator_;
}
// Returns maximum total bytes of data on a given level.
uint64_t MaxBytesForLevel(int level) const;
// Must be called after any change to MutableCFOptions.
void CalculateBaseBytes(const ImmutableCFOptions& ioptions,
const MutableCFOptions& options);
// Returns an estimate of the amount of live data in bytes.
uint64_t EstimateLiveDataSize() const;
uint64_t estimated_compaction_needed_bytes() const {
return estimated_compaction_needed_bytes_;
}
private:
const InternalKeyComparator* internal_comparator_;
const Comparator* user_comparator_;
int num_levels_; // Number of levels
int num_non_empty_levels_; // Number of levels. Any level larger than it
// is guaranteed to be empty.
// Per-level max bytes
std::vector<uint64_t> level_max_bytes_;
// A short brief metadata of files per level
autovector<rocksdb::LevelFilesBrief> level_files_brief_;
FileIndexer file_indexer_;
Arena arena_; // Used to allocate space for file_levels_
CompactionStyle compaction_style_;
// List of files per level, files in each level are arranged
// in increasing order of keys
std::vector<FileMetaData*>* files_;
// Level that L0 data should be compacted to. All levels < base_level_ should
// be empty. -1 if it is not level-compaction so it's not applicable.
int base_level_;
// A list for the same set of files that are stored in files_,
// but files in each level are now sorted based on file
// size. The file with the largest size is at the front.
// This vector stores the index of the file from files_.
std::vector<std::vector<int>> files_by_size_;
// If true, means that files in L0 have keys with non overlapping ranges
bool level0_non_overlapping_;
// An index into files_by_size_ that specifies the first
// file that is not yet compacted
std::vector<int> next_file_to_compact_by_size_;
// Only the first few entries of files_by_size_ are sorted.
// There is no need to sort all the files because it is likely
// that on a running system, we need to look at only the first
// few largest files because a new version is created every few
// seconds/minutes (because of concurrent compactions).
static const size_t number_of_files_to_sort_ = 50;
// This vector contains list of files marked for compaction and also not
// currently being compacted. It is protected by DB mutex. It is calculated in
// ComputeCompactionScore()
autovector<std::pair<int, FileMetaData*>> files_marked_for_compaction_;
// Level that should be compacted next and its compaction score.
// Score < 1 means compaction is not strictly needed. These fields
// are initialized by Finalize().
// The most critical level to be compacted is listed first
// These are used to pick the best compaction level
std::vector<double> compaction_score_;
std::vector<int> compaction_level_;
double max_compaction_score_ = 0.0; // max score in l1 to ln-1
int max_compaction_score_level_ = 0; // level on which max score occurs
int l0_delay_trigger_count_ = 0; // Count used to trigger slow down and stop
// for number of L0 files.
// the following are the sampled temporary stats.
// the current accumulated size of sampled files.
uint64_t accumulated_file_size_;
// the current accumulated size of all raw keys based on the sampled files.
uint64_t accumulated_raw_key_size_;
// the current accumulated size of all raw keys based on the sampled files.
uint64_t accumulated_raw_value_size_;
// total number of non-deletion entries
uint64_t accumulated_num_non_deletions_;
// total number of deletion entries
uint64_t accumulated_num_deletions_;
// the number of samples
uint64_t num_samples_;
// Estimated bytes needed to be compacted until all levels' size is down to
// target sizes.
uint64_t estimated_compaction_needed_bytes_;
bool finalized_;
friend class Version;
friend class VersionSet;
// No copying allowed
VersionStorageInfo(const VersionStorageInfo&) = delete;
void operator=(const VersionStorageInfo&) = delete;
};
class Version {
public:
// Append to *iters a sequence of iterators that will
// yield the contents of this Version when merged together.
// REQUIRES: This version has been saved (see VersionSet::SaveTo)
void AddIterators(const ReadOptions&, const EnvOptions& soptions,
MergeIteratorBuilder* merger_iter_builder);
// Lookup the value for key. If found, store it in *val and
// return OK. Else return a non-OK status.
// Uses *operands to store merge_operator operations to apply later
// REQUIRES: lock is not held
void Get(const ReadOptions&, const LookupKey& key, std::string* val,
Status* status, MergeContext* merge_context,
bool* value_found = nullptr);
// Loads some stats information from files. Call without mutex held. It needs
// to be called before applying the version to the version set.
void PrepareApply(const MutableCFOptions& mutable_cf_options,
bool update_stats);
// Reference count management (so Versions do not disappear out from
// under live iterators)
void Ref();
// Decrease reference count. Delete the object if no reference left
// and return true. Otherwise, return false.
bool Unref();
// Add all files listed in the current version to *live.
void AddLiveFiles(std::vector<FileDescriptor>* live);
// Return a human readable string that describes this version's contents.
std::string DebugString(bool hex = false) const;
// Returns the version nuber of this version
uint64_t GetVersionNumber() const { return version_number_; }
// REQUIRES: lock is held
// On success, "tp" will contains the table properties of the file
// specified in "file_meta". If the file name of "file_meta" is
// known ahread, passing it by a non-null "fname" can save a
// file-name conversion.
Status GetTableProperties(std::shared_ptr<const TableProperties>* tp,
const FileMetaData* file_meta,
const std::string* fname = nullptr);
// REQUIRES: lock is held
// On success, *props will be populated with all SSTables' table properties.
// The keys of `props` are the sst file name, the values of `props` are the
// tables' propertis, represented as shared_ptr.
Status GetPropertiesOfAllTables(TablePropertiesCollection* props);
Status GetPropertiesOfAllTables(TablePropertiesCollection* props, int level);
// REQUIRES: lock is held
// On success, "tp" will contains the aggregated table property amoug
// the table properties of all sst files in this version.
Status GetAggregatedTableProperties(
std::shared_ptr<const TableProperties>* tp, int level = -1);
uint64_t GetEstimatedActiveKeys() {
return storage_info_.GetEstimatedActiveKeys();
}
size_t GetMemoryUsageByTableReaders();
ColumnFamilyData* cfd() const { return cfd_; }
// Return the next Version in the linked list. Used for debug only
Version* TEST_Next() const {
return next_;
}
VersionStorageInfo* storage_info() { return &storage_info_; }
VersionSet* version_set() { return vset_; }
void GetColumnFamilyMetaData(ColumnFamilyMetaData* cf_meta);
private:
Env* env_;
friend class VersionSet;
const InternalKeyComparator* internal_comparator() const {
return storage_info_.internal_comparator_;
}
const Comparator* user_comparator() const {
return storage_info_.user_comparator_;
}
bool PrefixMayMatch(const ReadOptions& read_options, Iterator* level_iter,
const Slice& internal_prefix) const;
// The helper function of UpdateAccumulatedStats, which may fill the missing
// fields of file_mata from its associated TableProperties.
// Returns true if it does initialize FileMetaData.
bool MaybeInitializeFileMetaData(FileMetaData* file_meta);
// Update the accumulated stats associated with the current version.
// This accumulated stats will be used in compaction.
void UpdateAccumulatedStats(bool update_stats);
// Sort all files for this version based on their file size and
// record results in files_by_size_. The largest files are listed first.
void UpdateFilesBySize();
ColumnFamilyData* cfd_; // ColumnFamilyData to which this Version belongs
Logger* info_log_;
Statistics* db_statistics_;
TableCache* table_cache_;
const MergeOperator* merge_operator_;
VersionStorageInfo storage_info_;
VersionSet* vset_; // VersionSet to which this Version belongs
Version* next_; // Next version in linked list
Version* prev_; // Previous version in linked list
int refs_; // Number of live refs to this version
// A version number that uniquely represents this version. This is
// used for debugging and logging purposes only.
uint64_t version_number_;
Version(ColumnFamilyData* cfd, VersionSet* vset, uint64_t version_number = 0);
~Version();
// No copying allowed
Version(const Version&);
void operator=(const Version&);
};
class VersionSet {
public:
VersionSet(const std::string& dbname, const DBOptions* db_options,
const EnvOptions& env_options, Cache* table_cache,
WriteBuffer* write_buffer, WriteController* write_controller);
~VersionSet();
// Apply *edit to the current version to form a new descriptor that
// is both saved to persistent state and installed as the new
// current version. Will release *mu while actually writing to the file.
// column_family_options has to be set if edit is column family add
// REQUIRES: *mu is held on entry.
// REQUIRES: no other thread concurrently calls LogAndApply()
Status LogAndApply(
ColumnFamilyData* column_family_data,
const MutableCFOptions& mutable_cf_options, VersionEdit* edit,
InstrumentedMutex* mu, Directory* db_directory = nullptr,
bool new_descriptor_log = false,
const ColumnFamilyOptions* column_family_options = nullptr);
// Recover the last saved descriptor from persistent storage.
// If read_only == true, Recover() will not complain if some column families
// are not opened
Status Recover(const std::vector<ColumnFamilyDescriptor>& column_families,
bool read_only = false);
// Reads a manifest file and returns a list of column families in
// column_families.
static Status ListColumnFamilies(std::vector<std::string>* column_families,
const std::string& dbname, Env* env);
#ifndef ROCKSDB_LITE
// Try to reduce the number of levels. This call is valid when
// only one level from the new max level to the old
// max level containing files.
// The call is static, since number of levels is immutable during
// the lifetime of a RocksDB instance. It reduces number of levels
// in a DB by applying changes to manifest.
// For example, a db currently has 7 levels [0-6], and a call to
// to reduce to 5 [0-4] can only be executed when only one level
// among [4-6] contains files.
static Status ReduceNumberOfLevels(const std::string& dbname,
const Options* options,
const EnvOptions& env_options,
int new_levels);
// printf contents (for debugging)
Status DumpManifest(Options& options, std::string& manifestFileName,
bool verbose, bool hex = false, bool json = false);
#endif // ROCKSDB_LITE
// Return the current manifest file number
uint64_t manifest_file_number() const { return manifest_file_number_; }
uint64_t pending_manifest_file_number() const {
return pending_manifest_file_number_;
}
uint64_t current_next_file_number() const { return next_file_number_.load(); }
// Allocate and return a new file number
uint64_t NewFileNumber() { return next_file_number_.fetch_add(1); }
// Return the last sequence number.
uint64_t LastSequence() const {
return last_sequence_.load(std::memory_order_acquire);
}
// Set the last sequence number to s.
void SetLastSequence(uint64_t s) {
assert(s >= last_sequence_);
last_sequence_.store(s, std::memory_order_release);
}
// Mark the specified file number as used.
// REQUIRED: this is only called during single-threaded recovery
void MarkFileNumberUsedDuringRecovery(uint64_t number);
// Return the log file number for the log file that is currently
// being compacted, or zero if there is no such log file.
uint64_t prev_log_number() const { return prev_log_number_; }
// Returns the minimum log number such that all
// log numbers less than or equal to it can be deleted
uint64_t MinLogNumber() const {
uint64_t min_log_num = std::numeric_limits<uint64_t>::max();
for (auto cfd : *column_family_set_) {
// It's safe to ignore dropped column families here:
// cfd->IsDropped() becomes true after the drop is persisted in MANIFEST.
if (min_log_num > cfd->GetLogNumber() && !cfd->IsDropped()) {
min_log_num = cfd->GetLogNumber();
}
}
return min_log_num;
}
// Create an iterator that reads over the compaction inputs for "*c".
// The caller should delete the iterator when no longer needed.
Iterator* MakeInputIterator(Compaction* c);
// Add all files listed in any live version to *live.
void AddLiveFiles(std::vector<FileDescriptor>* live_list);
// Return the approximate size of data to be scanned for range [start, end)
// in levels [start_level, end_level). If end_level == 0 it will search
// through all non-empty levels
uint64_t ApproximateSize(Version* v, const Slice& start, const Slice& end,
int start_level = 0, int end_level = -1);
// Return the size of the current manifest file
uint64_t manifest_file_size() const { return manifest_file_size_; }
// verify that the files that we started with for a compaction
// still exist in the current version and in the same original level.
// This ensures that a concurrent compaction did not erroneously
// pick the same files to compact.
bool VerifyCompactionFileConsistency(Compaction* c);
Status GetMetadataForFile(uint64_t number, int* filelevel,
FileMetaData** metadata, ColumnFamilyData** cfd);
void GetLiveFilesMetaData(std::vector<LiveFileMetaData> *metadata);
void GetObsoleteFiles(std::vector<FileMetaData*>* files,
uint64_t min_pending_output);
ColumnFamilySet* GetColumnFamilySet() { return column_family_set_.get(); }
const EnvOptions& env_options() { return env_options_; }
static uint64_t GetNumLiveVersions(Version* dummy_versions);
static uint64_t GetTotalSstFilesSize(Version* dummy_versions);
private:
struct ManifestWriter;
friend class Version;
friend class DBImpl;
struct LogReporter : public log::Reader::Reporter {
Status* status;
virtual void Corruption(size_t bytes, const Status& s) override {
if (this->status->ok()) *this->status = s;
}
};
// ApproximateSize helper
uint64_t ApproximateSizeLevel0(Version* v, const LevelFilesBrief& files_brief,
const Slice& start, const Slice& end);
uint64_t ApproximateSize(Version* v, const FdWithKeyRange& f,
const Slice& key);
// Save current contents to *log
Status WriteSnapshot(log::Writer* log);
void AppendVersion(ColumnFamilyData* column_family_data, Version* v);
bool ManifestContains(uint64_t manifest_file_number,
const std::string& record) const;
ColumnFamilyData* CreateColumnFamily(const ColumnFamilyOptions& cf_options,
VersionEdit* edit);
std::unique_ptr<ColumnFamilySet> column_family_set_;
Env* const env_;
const std::string dbname_;
const DBOptions* const db_options_;
std::atomic<uint64_t> next_file_number_;
uint64_t manifest_file_number_;
uint64_t pending_manifest_file_number_;
std::atomic<uint64_t> last_sequence_;
uint64_t prev_log_number_; // 0 or backing store for memtable being compacted
// Opened lazily
unique_ptr<log::Writer> descriptor_log_;
// generates a increasing version number for every new version
uint64_t current_version_number_;
// Queue of writers to the manifest file
std::deque<ManifestWriter*> manifest_writers_;
// Current size of manifest file
uint64_t manifest_file_size_;
std::vector<FileMetaData*> obsolete_files_;
// env options for all reads and writes except compactions
const EnvOptions& env_options_;
// env options used for compactions. This is a copy of
// env_options_ but with readaheads set to readahead_compactions_.
const EnvOptions env_options_compactions_;
// No copying allowed
VersionSet(const VersionSet&);
void operator=(const VersionSet&);
void LogAndApplyCFHelper(VersionEdit* edit);
void LogAndApplyHelper(ColumnFamilyData* cfd, VersionBuilder* b, Version* v,
VersionEdit* edit, InstrumentedMutex* mu);
};
} // namespace rocksdb