DB represents a collection of buckets persisted to a file on disk. All data access is performed through transactions which can be obtained through the DB. All the functions on DB will return a ErrDatabaseNotOpen if accessed before Open() is called.

DB is referenced in 338 repositories



type DB struct {
	// When enabled, the database will perform a Check() after every commit.
	// A panic is issued if the database is in an inconsistent state. This
	// flag has a large performance impact so it should only be used for
	// debugging purposes.
	StrictMode bool

	// Setting the NoSync flag will cause the database to skip fsync()
	// calls after each commit. This can be useful when bulk loading data
	// into a database and you can restart the bulk load in the event of
	// a system failure or database corruption. Do not set this flag for
	// normal use.
	// If the package global IgnoreNoSync constant is true, this value is
	// ignored.  See the comment on that constant for more details.
	NoSync bool

	// When true, skips the truncate call when growing the database.
	// Setting this to true is only safe on non-ext3/ext4 systems.
	// Skipping truncation avoids preallocation of hard drive space and
	// bypasses a truncate() and fsync() syscall on remapping.
	NoGrowSync bool

	// If you want to read the entire database fast, you can set MmapFlag to
	// syscall.MAP_POPULATE on Linux 2.6.23+ for sequential read-ahead.
	MmapFlags int

	// MaxBatchSize is the maximum size of a batch. Default value is
	// copied from DefaultMaxBatchSize in Open.
	// If <=0, disables batching.
	// Do not change concurrently with calls to Batch.
	MaxBatchSize int

	// MaxBatchDelay is the maximum delay before a batch starts.
	// Default value is copied from DefaultMaxBatchDelay in Open.
	// If <=0, effectively disables batching.
	// Do not change concurrently with calls to Batch.
	MaxBatchDelay time.Duration

	// AllocSize is the amount of space allocated when the database
	// needs to create new pages. This is done to amortize the cost
	// of truncate() and fsync() when growing the data file.
	AllocSize int

	path     string
	file     *os.File
	lockfile *os.File // windows only
	dataref  []byte   // mmap'ed readonly, write throws SEGV
	data     *[maxMapSize]byte
	datasz   int
	filesz   int // current on disk file size
	meta0    *meta
	meta1    *meta
	pageSize int
	opened   bool
	rwtx     *Tx
	txs      []*Tx
	freelist *freelist
	stats    Stats

	pagePool sync.Pool

	batchMu sync.Mutex
	batch   *batch

	rwlock   sync.Mutex   // Allows only one writer at a time.
	metalock sync.Mutex   // Protects meta page access.
	mmaplock sync.RWMutex // Protects mmap access during remapping.
	statlock sync.RWMutex // Protects stats access.

	ops struct {
		writeAt func(b []byte, off int64) (n int, err error)

	// Read only mode.
	// When true, Update() and Begin(true) return ErrDatabaseReadOnly immediately.
	readOnly bool