leveldb

package
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 Go to latest Published: Aug 23, 2014 License: MIT Imports: 23 Imported by: 0

Documentation

Overview

Package leveldb provides implementation of LevelDB key/value database.

Create or open a database: 

db, err := leveldb.OpenFile("path/to/db", nil)
...
defer db.Close()
...

Read or modify the database content: 

// Remember that the contents of the returned slice should not be modified.
data, err := db.Get([]byte("key"), nil)
...
err = db.Put([]byte("key"), []byte("value"), nil)
...
err = db.Delete([]byte("key"), nil)
...

Iterate over database content: 

iter := db.NewIterator(nil, nil)
for iter.Next() {
	// Remember that the contents of the returned slice should not be modified, and
	// only valid until the next call to Next.
	key := iter.Key()
	value := iter.Value()
	...
}
iter.Release()
err = iter.Error()
...

Seek-then-Iterate: 

iter := db.NewIterator(nil, nil)
for ok := iter.Seek(key); ok; ok = iter.Next() {
	// Use key/value.
	...
}
iter.Release()
err = iter.Error()
...

Iterate over subset of database content: 

iter := db.NewIterator(&util.Range{Start: []byte("foo"), Limit: []byte("xoo")}, nil)
for iter.Next() {
	// Use key/value.
	...
}
iter.Release()
err = iter.Error()
...

Batch writes: 

batch := new(leveldb.Batch)
batch.Put([]byte("foo"), []byte("value"))
batch.Put([]byte("bar"), []byte("another value"))
batch.Delete([]byte("baz"))
err = db.Write(batch, nil)
...

Use bloom filter: 

o := &opt.Options{
	Filter: filter.NewBloomFilter(10),
}
db, err := leveldb.OpenFile("path/to/db", o)
...
defer db.Close()
...

Index

Constants

This section is empty.

Variables

View Source 
var (
	ErrNotFound         = util.ErrNotFound
	ErrSnapshotReleased = errors.New("leveldb: snapshot released")
	ErrIterReleased     = errors.New("leveldb: iterator released")
	ErrClosed           = errors.New("leveldb: closed")
)

Functions

This section is empty.

Types

type Batch 

type Batch struct {
	// contains filtered or unexported fields
}

Batch is a write batch.

func (*Batch) Delete 

func (b *Batch) Delete(key []byte)

Delete appends 'delete operation' of the given key to the batch. It is safe to modify the contents of the argument after Delete returns.

func (*Batch) Put 

func (b *Batch) Put(key, value []byte)

Put appends 'put operation' of the given key/value pair to the batch. It is safe to modify the contents of the argument after Put returns.

func (*Batch) Reset 

func (b *Batch) Reset()

Reset resets the batch.

type CorruptionType 

type CorruptionType int
const (
	CorruptedManifest CorruptionType = iota
	MissingFiles
)

type DB 

type DB struct {
	// contains filtered or unexported fields
}

DB is a LevelDB database.

func Open 

func Open(stor storage.Storage, o *opt.Options) (db *DB, err error)

Open opens or creates a DB for the given storage. The DB will be created if not exist, unless ErrorIfMissing is true. Also, if ErrorIfExist is true and the DB exist Open will returns os.ErrExist error.

Open will return an error with type of ErrCorrupted if corruption detected in the DB. Corrupted DB can be recovered with Recover function.

The returned DB instance is goroutine-safe. The DB must be closed after use, by calling Close method.

func OpenFile 

func OpenFile(path string, o *opt.Options) (db *DB, err error)

OpenFile opens or creates a DB for the given path. The DB will be created if not exist, unless ErrorIfMissing is true. Also, if ErrorIfExist is true and the DB exist OpenFile will returns os.ErrExist error.

OpenFile uses standard file-system backed storage implementation as desribed in the leveldb/storage package.

OpenFile will return an error with type of ErrCorrupted if corruption detected in the DB. Corrupted DB can be recovered with Recover function.

The returned DB instance is goroutine-safe. The DB must be closed after use, by calling Close method.

func Recover 

func Recover(stor storage.Storage, o *opt.Options) (db *DB, err error)

Recover recovers and opens a DB with missing or corrupted manifest files for the given storage. It will ignore any manifest files, valid or not. The DB must already exist or it will returns an error. Also, Recover will ignore ErrorIfMissing and ErrorIfExist options.

The returned DB instance is goroutine-safe. The DB must be closed after use, by calling Close method.

func RecoverFile 

func RecoverFile(path string, o *opt.Options) (db *DB, err error)

RecoverFile recovers and opens a DB with missing or corrupted manifest files for the given path. It will ignore any manifest files, valid or not. The DB must already exist or it will returns an error. Also, Recover will ignore ErrorIfMissing and ErrorIfExist options.

RecoverFile uses standard file-system backed storage implementation as desribed in the leveldb/storage package.

The returned DB instance is goroutine-safe. The DB must be closed after use, by calling Close method.

func (*DB) Close 

func (db *DB) Close() error

Close closes the DB. This will also releases any outstanding snapshot and abort any in-flight compaction.

It is not safe to close a DB until all outstanding iterators are released. It is valid to call Close multiple times. Other methods should not be called after the DB has been closed.

func (*DB) CompactRange 

func (db *DB) CompactRange(r util.Range) error

CompactRange compacts the underlying DB for the given key range. In particular, deleted and overwritten versions are discarded, and the data is rearranged to reduce the cost of operations needed to access the data. This operation should typically only be invoked by users who understand the underlying implementation.

A nil Range.Start is treated as a key before all keys in the DB. And a nil Range.Limit is treated as a key after all keys in the DB. Therefore if both is nil then it will compact entire DB.

func (*DB) Delete 

func (db *DB) Delete(key []byte, wo *opt.WriteOptions) error

Delete deletes the value for the given key. It returns ErrNotFound if the DB does not contain the key.

It is safe to modify the contents of the arguments after Delete returns.

func (*DB) Get 

func (db *DB) Get(key []byte, ro *opt.ReadOptions) (value []byte, err error)

Get gets the value for the given key. It returns ErrNotFound if the DB does not contain the key.

The returned slice is its own copy, it is safe to modify the contents of the returned slice. It is safe to modify the contents of the argument after Get returns.

func (*DB) GetProperty 

func (db *DB) GetProperty(name string) (value string, err error)

GetProperty returns value of the given property name.

Property names: 

leveldb.num-files-at-level{n}
	Returns the number of filer at level 'n'.
leveldb.stats
	Returns statistics of the underlying DB.
leveldb.sstables
	Returns sstables list for each level.

func (*DB) GetSnapshot 

func (db *DB) GetSnapshot() (*Snapshot, error)

GetSnapshot returns a latest snapshot of the underlying DB. A snapshot is a frozen snapshot of a DB state at a particular point in time. The content of snapshot are guaranteed to be consistent.

The snapshot must be released after use, by calling Release method.

func (*DB) NewIterator 

func (db *DB) NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator

NewIterator returns an iterator for the latest snapshot of the uderlying DB. The returned iterator is not goroutine-safe, but it is safe to use multiple iterators concurrently, with each in a dedicated goroutine. It is also safe to use an iterator concurrently with modifying its underlying DB. The resultant key/value pairs are guaranteed to be consistent.

Slice allows slicing the iterator to only contains keys in the given range. A nil Range.Start is treated as a key before all keys in the DB. And a nil Range.Limit is treated as a key after all keys in the DB.

The iterator must be released after use, by calling Release method.

Also read Iterator documentation of the leveldb/iterator package.

func (*DB) Put 

func (db *DB) Put(key, value []byte, wo *opt.WriteOptions) error

Put sets the value for the given key. It overwrites any previous value for that key; a DB is not a multi-map.

It is safe to modify the contents of the arguments after Put returns.

func (*DB) SizeOf 

func (db *DB) SizeOf(ranges []util.Range) (Sizes, error)

SizeOf calculates approximate sizes of the given key ranges. The length of the returned sizes are equal with the length of the given ranges. The returned sizes measure storage space usage, so if the user data compresses by a factor of ten, the returned sizes will be one-tenth the size of the corresponding user data size. The results may not include the sizes of recently written data.

func (*DB) Write 

func (db *DB) Write(b *Batch, wo *opt.WriteOptions) (err error)

Write apply the given batch to the DB. The batch will be applied sequentially.

It is safe to modify the contents of the arguments after Write returns.

type ErrCorrupted 

type ErrCorrupted struct {
	Type CorruptionType
	Err  error
}

ErrCorrupted is the type that wraps errors that indicate corruption in the database.

func (ErrCorrupted) Error 

func (e ErrCorrupted) Error() string

type Reader 

type Reader interface {
	Get(key []byte, ro *opt.ReadOptions) (value []byte, err error)
	NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator
}

Reader is the interface that wraps basic Get and NewIterator methods. This interface implemented by both DB and Snapshot.

type Sizes 

type Sizes []uint64

func (Sizes) Sum 

func (p Sizes) Sum() (n uint64)

Sum returns sum of the sizes.

type Snapshot 

type Snapshot struct {
	// contains filtered or unexported fields
}

Snapshot is a DB snapshot.

func (*Snapshot) Get 

func (snap *Snapshot) Get(key []byte, ro *opt.ReadOptions) (value []byte, err error)

Get gets the value for the given key. It returns ErrNotFound if the DB does not contain the key.

The caller should not modify the contents of the returned slice, but it is safe to modify the contents of the argument after Get returns.

func (*Snapshot) NewIterator 

func (snap *Snapshot) NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator

NewIterator returns an iterator for the snapshot of the uderlying DB. The returned iterator is not goroutine-safe, but it is safe to use multiple iterators concurrently, with each in a dedicated goroutine. It is also safe to use an iterator concurrently with modifying its underlying DB. The resultant key/value pairs are guaranteed to be consistent.

Slice allows slicing the iterator to only contains keys in the given range. A nil Range.Start is treated as a key before all keys in the DB. And a nil Range.Limit is treated as a key after all keys in the DB.

The iterator must be released after use, by calling Release method. Releasing the snapshot doesn't mean releasing the iterator too, the iterator would be still valid until released.

Also read Iterator documentation of the leveldb/iterator package.

func (*Snapshot) Release 

func (snap *Snapshot) Release()

Release releases the snapshot. This will not release any returned iterators, the iterators would still be valid until released or the underlying DB is closed.

Other methods should not be called after the snapshot has been released.

Source Files

View all Source files

Directories

Path Synopsis
Package cache provides interface and implementation of a cache algorithms.
 Package cache provides interface and implementation of a cache algorithms.
Package comparer provides interface and implementation for ordering sets of data.
 Package comparer provides interface and implementation for ordering sets of data.
Package filter provides interface and implementation of probabilistic data structure.
 Package filter provides interface and implementation of probabilistic data structure.
Package iterator provides interface and implementation to traverse over contents of a database.
 Package iterator provides interface and implementation to traverse over contents of a database.
Package journal reads and writes sequences of journals.
 Package journal reads and writes sequences of journals.
Package memdb provides in-memory key/value database implementation.
 Package memdb provides in-memory key/value database implementation.
Package opt provides sets of options used by LevelDB.
 Package opt provides sets of options used by LevelDB.
Package storage provides storage abstraction for LevelDB.
 Package storage provides storage abstraction for LevelDB.
Package table allows read and write sorted key/value.
 Package table allows read and write sorted key/value.
Package util provides utilities used throughout leveldb.
 Package util provides utilities used throughout leveldb.

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