iterator

Documentation

Overview

Package iterator provides interface and implementation to traverse over contents of a database.

Index

• Variables
• type CommonIterator
• type Iterator
  • func NewEmptyIterator(err error) Iterator
  • func NewIndexedIterator(index IteratorIndexer, strict bool) Iterator
  • func NewMergedIterator(iters []Iterator, cmp comparer.Comparer, strict bool) Iterator
• type IteratorIndexer
• type IteratorSeeker

Variables

var (
	ErrIterReleased = errors.New("leveldb/iterator: iterator released")
)

Types

type CommonIterator

type CommonIterator interface {
	IteratorSeeker

	// util.Releaser is the interface that wraps basic Release method.
	// When called Release will releases any resources associated with the
	// iterator.
	util.Releaser

	// util.ReleaseSetter is the interface that wraps the basic SetReleaser
	// method.
	util.ReleaseSetter

	// TODO: Remove this when ready.
	Valid() bool

	// Error returns any accumulated error. Exhausting all the key/value pairs
	// is not considered to be an error.
	Error() error
}

CommonIterator is the interface that wraps common interator methods.

type Iterator

type Iterator interface {
	CommonIterator

	// 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'.
	Key() []byte

	// Value 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'.
	Value() []byte
}

Iterator iterates over a DB's key/value pairs in key order.

When encouter an error any 'seeks method' will return false and will yield no key/value pairs. The error can be queried by calling the Error method. Calling Release is still necessary.

An iterator must be released after use, but it is not necessary to read an iterator until exhaustion. Also, an iterator is not necessarily goroutine-safe, but it is safe to use multiple iterators concurrently, with each in a dedicated goroutine.

func NewEmptyIterator

func NewEmptyIterator(err error) Iterator

NewEmptyIterator creates an empty iterator. The err parameter can be nil, but if not nil the given err will be returned by Error method.

func NewIndexedIterator

func NewIndexedIterator(index IteratorIndexer, strict bool) Iterator

NewIndexedIterator returns an indexed iterator. An index is iterator that returns another iterator, a data iterator. A data iterator is the iterator that contains actual key/value pairs.

If strict is true then error yield by data iterator will halt the indexed iterator, on contrary if strict is false then the indexed iterator will ignore those error and move on to the next index.

func NewMergedIterator

func NewMergedIterator(iters []Iterator, cmp comparer.Comparer, strict bool) Iterator

NewMergedIterator returns an iterator that merges its input. Walking the resultant iterator will return all key/value pairs of all input iterators in strictly increasing key order, as defined by cmp. The input's key ranges may overlap, but there are assumed to be no duplicate keys: if iters[i] contains a key k then iters[j] will not contain that key k. None of the iters may be nil.

If strict is true then error yield by any iterators will halt the merged iterator, on contrary if strict is false then the merged iterator will ignore those error and move on to the next iterator.

type IteratorIndexer

type IteratorIndexer interface {
	CommonIterator

	// Get returns a new data iterator for the current position, or nil if
	// done.
	Get() Iterator
}

IteratorIndexer is the interface that wraps CommonIterator and basic Get method. IteratorIndexer provides index for indexed iterator.

type IteratorSeeker

type IteratorSeeker interface {
	// First moves the iterator to the first key/value pair. If the iterator
	// only contains one key/value pair then First and Last whould moves
	// to the same key/value pair.
	// It returns whether such pair exist.
	First() bool

	// Last moves the iterator to the last key/value pair. If the iterator
	// only contains one key/value pair then First and Last whould moves
	// to the same key/value pair.
	// It returns whether such pair exist.
	Last() bool

	// Seek moves the iterator to the first key/value pair whose key is greater
	// than or equal to the given key.
	// It returns whether such pair exist.
	//
	// It is safe to modify the contents of the argument after Seek returns.
	Seek(key []byte) bool

	// Next moves the iterator to the next key/value pair.
	// It returns whether the iterator is exhausted.
	Next() bool

	// Prev moves the iterator to the previous key/value pair.
	// It returns whether the iterator is exhausted.
	Prev() bool
}

IteratorSeeker is the interface that wraps the 'seeks method'.