db

README

Tendermint DB

Common database interface for various database backends. Primarily meant for applications built on Tendermint, such as the Cosmos SDK, but can be used independently of these as well.

Minimum Go Version

Go 1.13+

Supported Database Backends

• GoLevelDB [stable]: A pure Go implementation of LevelDB (see below). Currently the default on-disk database used in the Cosmos SDK.

• MemDB [stable]: An in-memory database using Google's B-tree package. Has very high performance both for reads, writes, and range scans, but is not durable and will lose all data on process exit. Does not support transactions. Suitable for e.g. caches, working sets, and tests. Used for IAVL working sets when the pruning strategy allows it.

• LevelDB [experimental]: A Go wrapper around LevelDB. Uses LSM-trees for on-disk storage, which have good performance for write-heavy workloads, particularly on spinning disks, but requires periodic compaction to maintain decent read performance and reclaim disk space. Does not support transactions.

• BoltDB [experimental]: A fork of BoltDB. Uses B+trees for on-disk storage, which have good performance for read-heavy workloads and range scans. Supports serializable ACID transactions.

• RocksDB [experimental]: A Go wrapper around RocksDB. Similarly to LevelDB (above) it uses LSM-trees for on-disk storage, but is optimized for fast storage media such as SSDs and memory. Supports atomic transactions, but not full ACID transactions.

• BadgerDB [experimental]: A key-value database written as a pure-Go alternative to e.g. LevelDB and RocksDB, with LSM-tree storage. Makes use of multiple goroutines for performance, and includes advanced features such as serializable ACID transactions, write batches, compression, and more.

Meta-databases

• PrefixDB [stable]: A database which wraps another database and uses a static prefix for all keys. This allows multiple logical databases to be stored in a common underlying databases by using different namespaces. Used by the Cosmos SDK to give different modules their own namespaced database in a single application database.

• RemoteDB [experimental]: A database that connects to distributed Tendermint db instances via gRPC. This can help with detaching difficult deployments such as LevelDB, and can also ease dependency management for Tendermint developers.

Tests

To test common databases, run make test. If all databases are available on the local machine, use make test-all to test them all.

Documentation

Index

• Variables
• func FileExists(filePath string) bool
• func IsKeyInDomain(key, start, end []byte) bool
• type Batch
• type DB
• type Iterator
  • func IteratePrefix(db DB, prefix []byte) (Iterator, error)
• type PrefixDB
  • func NewPrefixDB(db DB, prefix []byte) *PrefixDB
  • func (pdb *PrefixDB) Close() error
  • func (pdb *PrefixDB) Delete(key []byte) error
  • func (pdb *PrefixDB) DeleteSync(key []byte) error
  • func (pdb *PrefixDB) Get(key []byte) ([]byte, error)
  • func (pdb *PrefixDB) Has(key []byte) (bool, error)
  • func (pdb *PrefixDB) Iterator(start, end []byte) (Iterator, error)
  • func (pdb *PrefixDB) NewBatch() Batch
  • func (pdb *PrefixDB) Print() error
  • func (pdb *PrefixDB) ReverseIterator(start, end []byte) (Iterator, error)
  • func (pdb *PrefixDB) Set(key []byte, value []byte) error
  • func (pdb *PrefixDB) SetSync(key []byte, value []byte) error
  • func (pdb *PrefixDB) Stats() map[string]string

Variables

var (
	// ErrBatchClosed is returned when a closed or written batch is used.
	ErrBatchClosed = errors.New("batch has been written or closed")

	// ErrKeyEmpty is returned when attempting to use an empty or nil key.
	ErrKeyEmpty = errors.New("key cannot be empty")

	// ErrValueNil is returned when attempting to set a nil value.
	ErrValueNil = errors.New("value cannot be nil")
)

Functions

func FileExists

func FileExists(filePath string) bool

func IsKeyInDomain

func IsKeyInDomain(key, start, end []byte) bool

See DB interface documentation for more information.

Types

type Batch

type Batch interface {
	// Set sets a key/value pair.
	// CONTRACT: key, value readonly []byte
	Set(key, value []byte) error

	// Delete deletes a key/value pair.
	// CONTRACT: key readonly []byte
	Delete(key []byte) error

	// Write writes the batch, possibly without flushing to disk. Only Close() can be called after,
	// other methods will error.
	Write() error

	// WriteSync writes the batch and flushes it to disk. Only Close() can be called after, other
	// methods will error.
	WriteSync() error

	// Close closes the batch. It is idempotent, but calls to other methods afterwards will error.
	Close() error
}

Batch represents a group of writes. They may or may not be written atomically depending on the backend. Callers must call Close on the batch when done.

As with DB, given keys and values should be considered read-only, and must not be modified after passing them to the batch.

type DB

type DB interface {
	// Get fetches the value of the given key, or nil if it does not exist.
	// CONTRACT: key, value readonly []byte
	Get([]byte) ([]byte, error)

	// Has checks if a key exists.
	// CONTRACT: key, value readonly []byte
	Has(key []byte) (bool, error)

	// Set sets the value for the given key, replacing it if it already exists.
	// CONTRACT: key, value readonly []byte
	Set([]byte, []byte) error

	// SetSync sets the value for the given key, and flushes it to storage before returning.
	SetSync([]byte, []byte) error

	// Delete deletes the key, or does nothing if the key does not exist.
	// CONTRACT: key readonly []byte
	Delete([]byte) error

	// DeleteSync deletes the key, and flushes the delete to storage before returning.
	DeleteSync([]byte) error

	// Iterator returns an iterator over a domain of keys, in ascending order. The caller must call
	// Close when done. End is exclusive, and start must be less than end. A nil start iterates
	// from the first key, and a nil end iterates to the last key (inclusive). Empty keys are not
	// valid.
	// CONTRACT: No writes may happen within a domain while an iterator exists over it.
	// CONTRACT: start, end readonly []byte
	Iterator(start, end []byte) (Iterator, error)

	// ReverseIterator returns an iterator over a domain of keys, in descending order. The caller
	// must call Close when done. End is exclusive, and start must be less than end. A nil end
	// iterates from the last key (inclusive), and a nil start iterates to the first key (inclusive).
	// Empty keys are not valid.
	// CONTRACT: No writes may happen within a domain while an iterator exists over it.
	// CONTRACT: start, end readonly []byte
	ReverseIterator(start, end []byte) (Iterator, error)

	// Close closes the database connection.
	Close() error

	// NewBatch creates a batch for atomic updates. The caller must call Batch.Close.
	NewBatch() Batch

	// Print is used for debugging.
	Print() error

	// Stats returns a map of property values for all keys and the size of the cache.
	Stats() map[string]string
}

DB is the main interface for all database backends. DBs are concurrency-safe. Callers must call Close on the database when done.

Keys cannot be nil or empty, while values cannot be nil. Keys and values should be considered read-only, both when returned and when given, and must be copied before they are modified.

type Iterator

type Iterator interface {
	// Domain returns the start (inclusive) and end (exclusive) limits of the iterator.
	// CONTRACT: start, end readonly []byte
	Domain() (start []byte, end []byte)

	// Valid returns whether the current iterator is valid. Once invalid, the Iterator remains
	// invalid forever.
	Valid() bool

	// Next moves the iterator to the next key in the database, as defined by order of iteration.
	// If Valid returns false, this method will panic.
	Next()

	// Key returns the key at the current position. Panics if the iterator is invalid.
	// CONTRACT: key readonly []byte
	Key() (key []byte)

	// Value returns the value at the current position. Panics if the iterator is invalid.
	// CONTRACT: value readonly []byte
	Value() (value []byte)

	// Error returns the last error encountered by the iterator, if any.
	Error() error

	// Close closes the iterator, relasing any allocated resources.
	Close() error
}

Iterator represents an iterator over a domain of keys. Callers must call Close when done. No writes can happen to a domain while there exists an iterator over it, some backends may take out database locks to ensure this will not happen.

Callers must make sure the iterator is valid before calling any methods on it, otherwise these methods will panic. This is in part caused by most backend databases using this convention.

As with DB, keys and values should be considered read-only, and must be copied before they are modified.

Typical usage:

var itr Iterator = ... defer itr.Close()

for ; itr.Valid(); itr.Next() {
  k, v := itr.Key(); itr.Value()
  ...
}

if err := itr.Error(); err != nil {
  ...
}

func IteratePrefix

func IteratePrefix(db DB, prefix []byte) (Iterator, error)

IteratePrefix is a convenience function for iterating over a key domain restricted by prefix.

type PrefixDB

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

PrefixDB wraps a namespace of another database as a logical database.

func NewPrefixDB

func NewPrefixDB(db DB, prefix []byte) *PrefixDB

NewPrefixDB lets you namespace multiple DBs within a single DB.

func (*PrefixDB) Close

func (pdb *PrefixDB) Close() error

Close implements DB.

func (*PrefixDB) Delete

func (pdb *PrefixDB) Delete(key []byte) error

Delete implements DB.

func (*PrefixDB) DeleteSync

func (pdb *PrefixDB) DeleteSync(key []byte) error

DeleteSync implements DB.

func (*PrefixDB) Get

func (pdb *PrefixDB) Get(key []byte) ([]byte, error)

Get implements DB.

func (*PrefixDB) Has

func (pdb *PrefixDB) Has(key []byte) (bool, error)

Has implements DB.

func (*PrefixDB) Iterator

func (pdb *PrefixDB) Iterator(start, end []byte) (Iterator, error)

Iterator implements DB.

func (*PrefixDB) NewBatch

func (pdb *PrefixDB) NewBatch() Batch

NewBatch implements DB.

func (*PrefixDB) Print

func (pdb *PrefixDB) Print() error

Print implements DB.

func (*PrefixDB) ReverseIterator

func (pdb *PrefixDB) ReverseIterator(start, end []byte) (Iterator, error)

ReverseIterator implements DB.

func (*PrefixDB) Set

func (pdb *PrefixDB) Set(key []byte, value []byte) error

Set implements DB.

func (*PrefixDB) SetSync

func (pdb *PrefixDB) SetSync(key []byte, value []byte) error

SetSync implements DB.

func (*PrefixDB) Stats

func (pdb *PrefixDB) Stats() map[string]string

Stats implements DB.