-
Notifications
You must be signed in to change notification settings - Fork 8.8k
/
iterator_combiner.go
133 lines (118 loc) · 4.33 KB
/
iterator_combiner.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
/*
Copyright IBM Corp. All Rights Reserved.
SPDX-License-Identifier: Apache-2.0
*/
package queryutil
import (
"fmt"
commonledger "github.com/hyperledger/fabric/common/ledger"
"github.com/hyperledger/fabric/core/ledger/kvledger/txmgmt/statedb"
"github.com/hyperledger/fabric/protos/ledger/queryresult"
)
type itrCombiner struct {
namespace string
holders []*itrHolder
}
func newItrCombiner(namespace string, baseIterators []statedb.ResultsIterator) (*itrCombiner, error) {
var holders []*itrHolder
for _, itr := range baseIterators {
res, err := itr.Next()
if err != nil {
for _, holder := range holders {
holder.itr.Close()
}
return nil, err
}
if res != nil {
holders = append(holders, &itrHolder{itr, res.(*statedb.VersionedKV)})
}
}
return &itrCombiner{namespace, holders}, nil
}
// Next returns the next eligible item from the underlying iterators.
// This function evaluates the underlying iterators, and picks the one which is
// gives the lexicographically smallest key. Then, it saves that value, and advances the chosen iterator.
// If the chosen iterator is out of elements, then that iterator is closed, and removed from the list of iterators.
func (combiner *itrCombiner) Next() (commonledger.QueryResult, error) {
logger.Debugf("Iterators position at beginning: %s", combiner.holders)
if len(combiner.holders) == 0 {
return nil, nil
}
smallestHolderIndex := 0
for i := 1; i < len(combiner.holders); i++ {
smallestKey, holderKey := combiner.keyAt(smallestHolderIndex), combiner.keyAt(i)
switch {
case holderKey == smallestKey: // we found the same key in the lower order iterator (stale value of the key);
// we already have the latest value for this key (in smallestHolder). Ignore this value and move the iterator
// to next item (to a greater key) so that for next round of key selection, we do not consider this key again
removed, err := combiner.moveItrAndRemoveIfExhausted(i)
if err != nil {
return nil, err
}
if removed { // if the current iterator is exhaused and hence removed, decrement the index
// because indexes of the remaining iterators are decremented by one
i--
}
case holderKey < smallestKey:
smallestHolderIndex = i
default:
// the current key under evaluation is greater than the smallestKey - do nothing
}
}
kv := combiner.kvAt(smallestHolderIndex)
combiner.moveItrAndRemoveIfExhausted(smallestHolderIndex)
if kv.IsDelete() {
return combiner.Next()
}
logger.Debugf("Key [%s] selected from iterator at index [%d]", kv.Key, smallestHolderIndex)
logger.Debugf("Iterators position at end: %s", combiner.holders)
return &queryresult.KV{Namespace: combiner.namespace, Key: kv.Key, Value: kv.Value}, nil
}
// moveItrAndRemoveIfExhausted moves the iterator at index i to the next item. If the iterator gets exhausted
// then the iterator is removed from the underlying slice
func (combiner *itrCombiner) moveItrAndRemoveIfExhausted(i int) (removed bool, err error) {
holder := combiner.holders[i]
exhausted, err := holder.moveToNext()
if err != nil {
return false, err
}
if exhausted {
combiner.holders[i].itr.Close()
combiner.holders = append(combiner.holders[:i], combiner.holders[i+1:]...)
}
return exhausted, nil
}
// kvAt returns the kv available from iterator at index i
func (combiner *itrCombiner) kvAt(i int) *statedb.VersionedKV {
return combiner.holders[i].kv
}
// keyAt returns the key available from iterator at index i
func (combiner *itrCombiner) keyAt(i int) string {
return combiner.kvAt(i).Key
}
// Close closes all the underlying iterators
func (combiner *itrCombiner) Close() {
for _, holder := range combiner.holders {
holder.itr.Close()
}
}
// itrHolder encloses an iterator and keeps the next item available from the iterator in the buffer
type itrHolder struct {
itr statedb.ResultsIterator
kv *statedb.VersionedKV
}
// moveToNext fetches the next item to keep in buffer and returns true if the iterator is exhausted
func (holder *itrHolder) moveToNext() (exhausted bool, err error) {
var res statedb.QueryResult
if res, err = holder.itr.Next(); err != nil {
return false, err
}
if res != nil {
holder.kv = res.(*statedb.VersionedKV)
}
return res == nil, nil
}
// String returns the key that the holder has in the buffer for serving as a next key
func (holder *itrHolder) String() string {
return fmt.Sprintf("{%s}", holder.kv.Key)
}