db

Documentation

Index

• type Batch
• type DB
• type Iterator

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(key []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(key []byte, value []byte) error

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

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

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

	// Compact explicitly
	Compact(start, end []byte) error
}

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.
	// Key returns the key of the current key/value pair, or nil if done.
	// The caller should not modify the contents of the returned slice, and
	// its contents may change on the next call to any 'seeks method'.
	// Instead, the caller should make a copy and work on the copy.
	Key() (key []byte)

	// Value returns the value at the current position. Panics if the iterator is invalid.
	// Value returns the value of the current key/value pair, or nil if done.
	// The caller should not modify the contents of the returned slice, and
	// its contents may change on the next call to any 'seeks method'.
	// Instead, the caller should make a copy and work on the copy.
	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 {
  ...
}