Example #1
0
// Open opens a LevelDB whose files live in the given directory.
func Open(dirname string, opts *db.Options) (*DB, error) {
	d := &DB{
		dirname:        dirname,
		opts:           opts,
		icmp:           internalKeyComparer{opts.GetComparer()},
		pendingOutputs: make(map[uint64]struct{}),
	}
	if opts != nil {
		d.icmpOpts = *opts
	}
	d.icmpOpts.Comparer = d.icmp
	tableCacheSize := opts.GetMaxOpenFiles() - numNonTableCacheFiles
	if tableCacheSize < minTableCacheSize {
		tableCacheSize = minTableCacheSize
	}
	// tableCache初始化
	d.tableCache.init(dirname, opts.GetFileSystem(), &d.icmpOpts, tableCacheSize)
	// 初始化一个MemDB
	d.mem = memdb.New(&d.icmpOpts)

	// sync.Cond在Locker的基础上增加的一个消息通知的功能。
	// Cond有三个方法:Wait,Signal,Broadcast。
	// Wait添加一个计数,也就是添加一个阻塞的goroutine。
	// Signal解除一个goroutine的阻塞,计数减一。
	// Broadcast接触所有wait goroutine的阻塞。
	d.compactionCond = sync.Cond{L: &d.mu}
	fs := opts.GetFileSystem()

	d.mu.Lock()
	defer d.mu.Unlock()

	// Lock the database directory.
	// If the directory already exists, MkdirAll does nothing and returns nil.
	// 如果目录已经存在,则MkdirAll啥都不干
	err := fs.MkdirAll(dirname, 0755)
	if err != nil {
		return nil, err
	}
	// 创建LOCK文件,并加文件锁
	fileLock, err := fs.Lock(dbFilename(dirname, fileTypeLock, 0))
	if err != nil {
		return nil, err
	}
	defer func() {
		if fileLock != nil {
			fileLock.Close()
		}
	}()

	// 若CURRENT文件不存在,则调用createDB
	if _, err := fs.Stat(dbFilename(dirname, fileTypeCurrent, 0)); os.IsNotExist(err) {
		// Create the DB if it did not already exist.
		if err := createDB(dirname, opts); err != nil {
			return nil, err
		}
	} else if err != nil {
		return nil, fmt.Errorf("leveldb: database %q: %v", dirname, err)
	} else if opts.GetErrorIfDBExists() {
		return nil, fmt.Errorf("leveldb: database %q already exists", dirname)
	}

	// Load the version set.
	// 先读取CURRENT文件内容,获取manifest文件名,然后逐条记录读取manifest文件的内容,根据内容生成一个新version,放入d.versions中
	err = d.versions.load(dirname, opts)
	if err != nil {
		return nil, err
	}

	// Replay any newer log files than the ones named in the manifest.
	var ve versionEdit
	ls, err := fs.List(dirname)
	if err != nil {
		return nil, err
	}
	var logFiles fileNumAndNameSlice
	for _, filename := range ls {
		ft, fn, ok := parseDBFilename(filename)
		if ok && ft == fileTypeLog && (fn >= d.versions.logNumber || fn == d.versions.prevLogNumber) {
			logFiles = append(logFiles, fileNumAndName{fn, filename})
		}
	}
	sort.Sort(logFiles)
	for _, lf := range logFiles {
		// 根据日志文件重做日志中记录的操作,先将这些操作记录存入一个临时的memtable中,然后转存入磁盘上level0存储文件中
		maxSeqNum, err := d.replayLogFile(&ve, fs, filepath.Join(dirname, lf.name))
		if err != nil {
			return nil, err
		}
		d.versions.markFileNumUsed(lf.num)
		// 设置最新的操作序列号
		if d.versions.lastSequence < maxSeqNum {
			d.versions.lastSequence = maxSeqNum
		}
	}

	// Create an empty .log file.
	// 创建一个新的空log文件
	ve.logNumber = d.versions.nextFileNum()
	d.logNumber = ve.logNumber
	logFile, err := fs.Create(dbFilename(dirname, fileTypeLog, ve.logNumber))
	if err != nil {
		return nil, err
	}
	defer func() {
		if logFile != nil {
			logFile.Close()
		}
	}()
	d.log = record.NewWriter(logFile)

	// Write a new manifest to disk.
	// 根据前面重做日志得到的ve的信息创建一个新的manifest文件
	// 并在CURRENT文件中指向这个新manifest文件
	if err := d.versions.logAndApply(dirname, &ve); err != nil {
		return nil, err
	}

	d.deleteObsoleteFiles()
	// 尝试调度compaction
	d.maybeScheduleCompaction()

	d.logFile, logFile = logFile, nil
	d.fileLock, fileLock = fileLock, nil
	return d, nil
}
Example #2
0
// Open opens a LevelDB whose files live in the given directory.
func Open(dirname string, opts *db.Options) (*DB, error) {
	d := &DB{
		dirname:        dirname,
		opts:           opts,
		icmp:           internalKeyComparer{opts.GetComparer()},
		pendingOutputs: make(map[uint64]struct{}),
	}
	if opts != nil {
		d.icmpOpts = *opts
	}
	d.icmpOpts.Comparer = d.icmp
	tableCacheSize := opts.GetMaxOpenFiles() - numNonTableCacheFiles
	if tableCacheSize < minTableCacheSize {
		tableCacheSize = minTableCacheSize
	}
	d.tableCache.init(dirname, opts.GetFileSystem(), &d.icmpOpts, tableCacheSize)
	d.mem = memdb.New(&d.icmpOpts)
	d.compactionCond = sync.Cond{L: &d.mu}
	fs := opts.GetFileSystem()

	d.mu.Lock()
	defer d.mu.Unlock()

	// Lock the database directory.
	err := fs.MkdirAll(dirname, 0755)
	if err != nil {
		return nil, err
	}
	fileLock, err := fs.Lock(dbFilename(dirname, fileTypeLock, 0))
	if err != nil {
		return nil, err
	}
	defer func() {
		if fileLock != nil {
			fileLock.Close()
		}
	}()

	if _, err := fs.Stat(dbFilename(dirname, fileTypeCurrent, 0)); os.IsNotExist(err) {
		// Create the DB if it did not already exist.
		if err := createDB(dirname, opts); err != nil {
			return nil, err
		}
	} else if err != nil {
		return nil, fmt.Errorf("leveldb: database %q: %v", dirname, err)
	} else if opts.GetErrorIfDBExists() {
		return nil, fmt.Errorf("leveldb: database %q already exists", dirname)
	}

	// Load the version set.
	err = d.versions.load(dirname, opts)
	if err != nil {
		return nil, err
	}

	// Replay any newer log files than the ones named in the manifest.
	var ve versionEdit
	ls, err := fs.List(dirname)
	if err != nil {
		return nil, err
	}
	var logFiles fileNumAndNameSlice
	for _, filename := range ls {
		ft, fn, ok := parseDBFilename(filename)
		if ok && ft == fileTypeLog && (fn >= d.versions.logNumber || fn == d.versions.prevLogNumber) {
			logFiles = append(logFiles, fileNumAndName{fn, filename})
		}
	}
	sort.Sort(logFiles)
	for _, lf := range logFiles {
		maxSeqNum, err := d.replayLogFile(&ve, fs, filepath.Join(dirname, lf.name))
		if err != nil {
			return nil, err
		}
		d.versions.markFileNumUsed(lf.num)
		if d.versions.lastSequence < maxSeqNum {
			d.versions.lastSequence = maxSeqNum
		}
	}

	// Create an empty .log file.
	ve.logNumber = d.versions.nextFileNum()
	d.logNumber = ve.logNumber
	logFile, err := fs.Create(dbFilename(dirname, fileTypeLog, ve.logNumber))
	if err != nil {
		return nil, err
	}
	defer func() {
		if logFile != nil {
			logFile.Close()
		}
	}()
	d.log = record.NewWriter(logFile)

	// Write a new manifest to disk.
	if err := d.versions.logAndApply(dirname, &ve); err != nil {
		return nil, err
	}

	d.deleteObsoleteFiles()
	d.maybeScheduleCompaction()

	d.logFile, logFile = logFile, nil
	d.fileLock, fileLock = fileLock, nil
	return d, nil
}