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_);