forked from cayleygraph/cayley
/
iterator.go
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/
iterator.go
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// Copyright 2014 The Cayley Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package leveldb
import (
"bytes"
"encoding/json"
"github.com/barakmich/glog"
ldbit "github.com/syndtr/goleveldb/leveldb/iterator"
"github.com/syndtr/goleveldb/leveldb/opt"
"github.com/google/cayley/graph"
"github.com/google/cayley/graph/iterator"
"github.com/google/cayley/quad"
)
type Iterator struct {
uid uint64
tags graph.Tagger
nextPrefix []byte
checkID []byte
dir quad.Direction
open bool
iter ldbit.Iterator
qs *QuadStore
ro *opt.ReadOptions
originalPrefix string
result graph.Value
}
func NewIterator(prefix string, d quad.Direction, value graph.Value, qs *QuadStore) *Iterator {
vb := value.(Token)
p := make([]byte, 0, 2+hashSize)
p = append(p, []byte(prefix)...)
p = append(p, []byte(vb[1:])...)
opts := &opt.ReadOptions{
DontFillCache: true,
}
it := Iterator{
uid: iterator.NextUID(),
nextPrefix: p,
checkID: vb,
dir: d,
originalPrefix: prefix,
ro: opts,
iter: qs.db.NewIterator(nil, opts),
open: true,
qs: qs,
}
ok := it.iter.Seek(it.nextPrefix)
if !ok {
it.open = false
it.iter.Release()
glog.Error("Opening LevelDB iterator couldn't seek to location ", it.nextPrefix)
}
return &it
}
func (it *Iterator) UID() uint64 {
return it.uid
}
func (it *Iterator) Reset() {
if !it.open {
it.iter = it.qs.db.NewIterator(nil, it.ro)
it.open = true
}
ok := it.iter.Seek(it.nextPrefix)
if !ok {
it.open = false
it.iter.Release()
}
}
func (it *Iterator) Tagger() *graph.Tagger {
return &it.tags
}
func (it *Iterator) TagResults(dst map[string]graph.Value) {
for _, tag := range it.tags.Tags() {
dst[tag] = it.Result()
}
for tag, value := range it.tags.Fixed() {
dst[tag] = value
}
}
func (it *Iterator) Clone() graph.Iterator {
out := NewIterator(it.originalPrefix, it.dir, Token(it.checkID), it.qs)
out.tags.CopyFrom(it)
return out
}
func (it *Iterator) Close() error {
if it.open {
it.iter.Release()
it.open = false
}
return nil
}
func (it *Iterator) isLiveValue(val []byte) bool {
var entry IndexEntry
json.Unmarshal(val, &entry)
return len(entry.History)%2 != 0
}
func (it *Iterator) Next() bool {
if it.iter == nil {
it.result = nil
return false
}
if !it.open {
it.result = nil
return false
}
if !it.iter.Valid() {
it.result = nil
it.Close()
return false
}
if bytes.HasPrefix(it.iter.Key(), it.nextPrefix) {
if !it.isLiveValue(it.iter.Value()) {
return it.Next()
}
out := make([]byte, len(it.iter.Key()))
copy(out, it.iter.Key())
it.result = Token(out)
ok := it.iter.Next()
if !ok {
it.Close()
}
return true
}
it.Close()
it.result = nil
return false
}
func (it *Iterator) Err() error {
return it.iter.Error()
}
func (it *Iterator) ResultTree() *graph.ResultTree {
return graph.NewResultTree(it.Result())
}
func (it *Iterator) Result() graph.Value {
return it.result
}
func (it *Iterator) NextPath() bool {
return false
}
// No subiterators.
func (it *Iterator) SubIterators() []graph.Iterator {
return nil
}
func PositionOf(prefix []byte, d quad.Direction, qs *QuadStore) int {
if bytes.Equal(prefix, []byte("sp")) {
switch d {
case quad.Subject:
return 2
case quad.Predicate:
return hashSize + 2
case quad.Object:
return 2*hashSize + 2
case quad.Label:
return 3*hashSize + 2
}
}
if bytes.Equal(prefix, []byte("po")) {
switch d {
case quad.Subject:
return 2*hashSize + 2
case quad.Predicate:
return 2
case quad.Object:
return hashSize + 2
case quad.Label:
return hashSize + 2
}
}
if bytes.Equal(prefix, []byte("os")) {
switch d {
case quad.Subject:
return hashSize + 2
case quad.Predicate:
return 2*hashSize + 2
case quad.Object:
return 2
case quad.Label:
return 3*hashSize + 2
}
}
if bytes.Equal(prefix, []byte("cp")) {
switch d {
case quad.Subject:
return 2*hashSize + 2
case quad.Predicate:
return hashSize + 2
case quad.Object:
return 3*hashSize + 2
case quad.Label:
return 2
}
}
panic("unreachable")
}
func (it *Iterator) Contains(v graph.Value) bool {
val := v.(Token)
if val[0] == 'z' {
return false
}
offset := PositionOf(val[0:2], it.dir, it.qs)
if bytes.HasPrefix(val[offset:], it.checkID[1:]) {
// You may ask, why don't we check to see if it's a valid (not deleted) quad
// again?
//
// We've already done that -- in order to get the graph.Value token in the
// first place, we had to have done the check already; it came from a Next().
//
// However, if it ever starts coming from somewhere else, it'll be more
// efficient to change the interface of the graph.Value for LevelDB to a
// struct with a flag for isValid, to save another random read.
return true
}
return false
}
func (it *Iterator) Size() (int64, bool) {
return it.qs.SizeOf(Token(it.checkID)), true
}
func (it *Iterator) Describe() graph.Description {
size, _ := it.Size()
return graph.Description{
UID: it.UID(),
Name: it.qs.NameOf(Token(it.checkID)),
Type: it.Type(),
Tags: it.tags.Tags(),
Size: size,
Direction: it.dir,
}
}
var levelDBType graph.Type
func init() {
levelDBType = graph.RegisterIterator("leveldb")
}
func Type() graph.Type { return levelDBType }
func (it *Iterator) Type() graph.Type { return levelDBType }
func (it *Iterator) Sorted() bool { return false }
func (it *Iterator) Optimize() (graph.Iterator, bool) {
return it, false
}
func (it *Iterator) Stats() graph.IteratorStats {
s, _ := it.Size()
return graph.IteratorStats{
ContainsCost: 1,
NextCost: 2,
Size: s,
}
}
var _ graph.Nexter = &Iterator{}