LevelDB场景分析1--整体结构分析

基本用法

数据结构

class DBImpl : public DB

{

private:

struct CompactionState;

struct Writer;// Information kept for every waiting writer

Env* const env_; // 文件，目录，日志，Schedule线程

const InternalKeyComparator internal_comparator_;

const InternalFilterPolicy internal_filter_policy_; // 提高随机读的性能

const Options options_; // Options to control the behavior of a database (passed to DB::Open)

bool owns_info_log_;

bool owns_cache_;

const std::string dbname_;

// table_cache_ provides its own synchronization

TableCache* table_cache_;

// Lock over the persistent DB state. Non-NULL iff successfully acquired.

FileLock* db_lock_;

// State below is protected by mutex_

port::Mutex mutex_;

port::AtomicPointer shutting_down_;

port::CondVar bg_cv_; // Signalled when background work finishes

MemTable* mem_;

MemTable* imm_; // Memtable being compacted

port::AtomicPointer has_imm_; // So bg thread can detect non-NULL imm_

WritableFile* logfile_;

uint64_t logfile_number_;

log::Writer* log_;

uint32_t seed_; // For sampling.

// Queue of writers.

std::deque<Writer*> writers_;

WriteBatch* tmp_batch_;

SnapshotList snapshots_;

// Set of table files to protect from deletion because they are

// part of ongoing compactions.

std::set<uint64_t> pending_outputs_;

// Has a background compaction been scheduled or is running?

bool bg_compaction_scheduled_;

ManualCompaction* manual_compaction_;

VersionSet* versions_;

// Have we encountered a background error in paranoid mode?

Status bg_error_;

CompactionStats stats_[config::kNumLevels];

};

红色部分成员是需要重点关注的。

主要场景

public:

Status DB::Open(const Options& options, const std::string& dbname, DB** dbptr)
// Implementations of the DB interface

virtual Status Put(const WriteOptions&, const Slice& key, const Slice& value);

virtual Status Delete(const WriteOptions&, const Slice& key);

virtual Status Write(const WriteOptions& options, WriteBatch* updates);

virtual Status Get(const ReadOptions& options,

const Slice& key,

std::string* value);

virtual Iterator* NewIterator(const ReadOptions&);

virtual const Snapshot* GetSnapshot();

virtual void ReleaseSnapshot(const Snapshot* snapshot);

virtual bool GetProperty(const Slice& property, std::string* value);

virtual void GetApproximateSizes(const Range* range, int n, uint64_t* sizes);

virtual void CompactRange(const Slice* begin, const Slice* end);

// Extra methods (for testing) that are not in the public DB interface

// Record a sample of bytes read at the specified internal key.

// Samples are taken approximately once every config::kReadBytesPeriod

// bytes.

void RecordReadSample(Slice key);

private:

Iterator* NewInternalIterator(const ReadOptions&,

SequenceNumber* latest_snapshot,

uint32_t* seed);

Status NewDB();

// Recover the descriptor from persistent storage. May do a significant

// amount of work to recover recently logged updates. Any changes to

// be made to the descriptor are added to *edit.

Status Recover(VersionEdit* edit) EXCLUSIVE_LOCKS_REQUIRED(mutex_);

void MaybeIgnoreError(Status* s) const;

// Delete any unneeded files and stale in-memory entries.

void DeleteObsoleteFiles();

// Compact the in-memory write buffer to disk. Switches to a new

// log-file/memtable and writes a new descriptor iff successful.

// Errors are recorded in bg_error_.

void CompactMemTable() EXCLUSIVE_LOCKS_REQUIRED(mutex_);

Status RecoverLogFile(uint64_t log_number,

VersionEdit* edit,

SequenceNumber* max_sequence)

EXCLUSIVE_LOCKS_REQUIRED(mutex_);

Status WriteLevel0Table(MemTable* mem, VersionEdit* edit, Version* base)

EXCLUSIVE_LOCKS_REQUIRED(mutex_);

Status MakeRoomForWrite(bool force /* compact even if there is room? */)

EXCLUSIVE_LOCKS_REQUIRED(mutex_);

WriteBatch* BuildBatchGroup(Writer** last_writer);

void RecordBackgroundError(const Status& s);

void MaybeScheduleCompaction() EXCLUSIVE_LOCKS_REQUIRED(mutex_);

static void BGWork(void* db);

void BackgroundCall();

void BackgroundCompaction() EXCLUSIVE_LOCKS_REQUIRED(mutex_);

void CleanupCompaction(CompactionState* compact)

EXCLUSIVE_LOCKS_REQUIRED(mutex_);

Status DoCompactionWork(CompactionState* compact)

EXCLUSIVE_LOCKS_REQUIRED(mutex_);

Status OpenCompactionOutputFile(CompactionState* compact);

Status FinishCompactionOutputFile(CompactionState* compact, Iterator* input);

Status InstallCompactionResults(CompactionState* compact)

EXCLUSIVE_LOCKS_REQUIRED(mutex_);

综合介绍

LevelDB主要有以下几个部分的内存开销：memtable,immutable table,table cache,block cache

memtable和immutable table的大小由 options_.write_buffer_size决定。

table cache由max_open_files决定数量。

block cache最大可以传入 size_t的大小。

由于使用了mmap，因此需要尽量使内存大于数据规模。否则可能造成随机读爆慢。

巴特西

LevelDB场景分析1--整体结构分析

基本用法

数据结构

主要场景

综合介绍

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