1// Copyright 2016 The etcd Authors
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//     http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15package raft
16
17import pb "go.etcd.io/etcd/raft/raftpb"
18
19// ReadState provides state for read only query.
20// It's caller's responsibility to call ReadIndex first before getting
21// this state from ready, it's also caller's duty to differentiate if this
22// state is what it requests through RequestCtx, eg. given a unique id as
23// RequestCtx
24type ReadState struct {
25	Index      uint64
26	RequestCtx []byte
27}
28
29type readIndexStatus struct {
30	req   pb.Message
31	index uint64
32	// NB: this never records 'false', but it's more convenient to use this
33	// instead of a map[uint64]struct{} due to the API of quorum.VoteResult. If
34	// this becomes performance sensitive enough (doubtful), quorum.VoteResult
35	// can change to an API that is closer to that of CommittedIndex.
36	acks map[uint64]bool
37}
38
39type readOnly struct {
40	option           ReadOnlyOption
41	pendingReadIndex map[string]*readIndexStatus
42	readIndexQueue   []string
43}
44
45func newReadOnly(option ReadOnlyOption) *readOnly {
46	return &readOnly{
47		option:           option,
48		pendingReadIndex: make(map[string]*readIndexStatus),
49	}
50}
51
52// addRequest adds a read only reuqest into readonly struct.
53// `index` is the commit index of the raft state machine when it received
54// the read only request.
55// `m` is the original read only request message from the local or remote node.
56func (ro *readOnly) addRequest(index uint64, m pb.Message) {
57	s := string(m.Entries[0].Data)
58	if _, ok := ro.pendingReadIndex[s]; ok {
59		return
60	}
61	ro.pendingReadIndex[s] = &readIndexStatus{index: index, req: m, acks: make(map[uint64]bool)}
62	ro.readIndexQueue = append(ro.readIndexQueue, s)
63}
64
65// recvAck notifies the readonly struct that the raft state machine received
66// an acknowledgment of the heartbeat that attached with the read only request
67// context.
68func (ro *readOnly) recvAck(id uint64, context []byte) map[uint64]bool {
69	rs, ok := ro.pendingReadIndex[string(context)]
70	if !ok {
71		return nil
72	}
73
74	rs.acks[id] = true
75	return rs.acks
76}
77
78// advance advances the read only request queue kept by the readonly struct.
79// It dequeues the requests until it finds the read only request that has
80// the same context as the given `m`.
81func (ro *readOnly) advance(m pb.Message) []*readIndexStatus {
82	var (
83		i     int
84		found bool
85	)
86
87	ctx := string(m.Context)
88	rss := []*readIndexStatus{}
89
90	for _, okctx := range ro.readIndexQueue {
91		i++
92		rs, ok := ro.pendingReadIndex[okctx]
93		if !ok {
94			panic("cannot find corresponding read state from pending map")
95		}
96		rss = append(rss, rs)
97		if okctx == ctx {
98			found = true
99			break
100		}
101	}
102
103	if found {
104		ro.readIndexQueue = ro.readIndexQueue[i:]
105		for _, rs := range rss {
106			delete(ro.pendingReadIndex, string(rs.req.Entries[0].Data))
107		}
108		return rss
109	}
110
111	return nil
112}
113
114// lastPendingRequestCtx returns the context of the last pending read only
115// request in readonly struct.
116func (ro *readOnly) lastPendingRequestCtx() string {
117	if len(ro.readIndexQueue) == 0 {
118		return ""
119	}
120	return ro.readIndexQueue[len(ro.readIndexQueue)-1]
121}
122