From 745431fcdaa64a320dffca4081184153e7ab5373 Mon Sep 17 00:00:00 2001
From: Tobias Schottdorf <tobias.schottdorf@gmail.com>
Date: Fri, 28 Jun 2019 18:08:44 +0200
Subject: [PATCH] raft/tracker: pull Voters and Learners into Config struct

This is helpful to quickly print the configuration log messages without
having to specify Voters and Learners separately.

It will also come in handy for joint quorums because it allows holding
on to voters and learners as a unit, which is useful for unit testing.
---
 raft/quorum/joint.go    |  7 +++++++
 raft/quorum/majority.go | 18 ++++++++++++++++++
 raft/quorum/quorum.go   |  1 +
 raft/raft.go            |  1 +
 raft/tracker/tracker.go | 31 +++++++++++++++++++++++++------
 5 files changed, 52 insertions(+), 6 deletions(-)

diff --git a/raft/quorum/joint.go b/raft/quorum/joint.go
index 9f8f484dc571..e3741e0b0a96 100644
--- a/raft/quorum/joint.go
+++ b/raft/quorum/joint.go
@@ -18,6 +18,13 @@ package quorum
 // majority configurations. Decisions require the support of both majorities.
 type JointConfig [2]MajorityConfig
 
+func (c JointConfig) String() string {
+	if len(c[1]) > 0 {
+		return c[0].String() + "&&" + c[1].String()
+	}
+	return c[0].String()
+}
+
 // IDs returns a newly initialized map representing the set of voters present
 // in the joint configuration.
 func (c JointConfig) IDs() map[uint64]struct{} {
diff --git a/raft/quorum/majority.go b/raft/quorum/majority.go
index 3d7bf82335ab..2770e34aec1a 100644
--- a/raft/quorum/majority.go
+++ b/raft/quorum/majority.go
@@ -24,6 +24,24 @@ import (
 // MajorityConfig is a set of IDs that uses majority quorums to make decisions.
 type MajorityConfig map[uint64]struct{}
 
+func (c MajorityConfig) String() string {
+	sl := make([]uint64, 0, len(c))
+	for id := range c {
+		sl = append(sl, id)
+	}
+	sort.Slice(sl, func(i, j int) bool { return sl[i] < sl[j] })
+	var buf strings.Builder
+	buf.WriteByte('(')
+	for i := range sl {
+		if i > 0 {
+			buf.WriteByte(' ')
+		}
+		buf.WriteString(fmt.Sprintf("%d", sl[i]))
+	}
+	buf.WriteByte(')')
+	return buf.String()
+}
+
 // Describe returns a (multi-line) representation of the commit indexes for the
 // given lookuper.
 func (c MajorityConfig) Describe(l AckedIndexer) string {
diff --git a/raft/quorum/quorum.go b/raft/quorum/quorum.go
index ff9c6f48d895..2899e46c96dc 100644
--- a/raft/quorum/quorum.go
+++ b/raft/quorum/quorum.go
@@ -19,6 +19,7 @@ import (
 	"strconv"
 )
 
+// Index is a Raft log position.
 type Index uint64
 
 func (i Index) String() string {
diff --git a/raft/raft.go b/raft/raft.go
index de473a45b744..f01ec0cf4309 100644
--- a/raft/raft.go
+++ b/raft/raft.go
@@ -1460,6 +1460,7 @@ func (r *raft) applyConfChange(cc pb.ConfChange) pb.ConfState {
 		}
 	}
 
+	r.logger.Infof("%x switched to configuration %s", r.id, r.prs.Config)
 	// Now that the configuration is updated, handle any side effects.
 
 	cs := pb.ConfState{Nodes: r.prs.VoterNodes(), Learners: r.prs.LearnerNodes()}
diff --git a/raft/tracker/tracker.go b/raft/tracker/tracker.go
index 2d162c6de05d..9e78010ce8d5 100644
--- a/raft/tracker/tracker.go
+++ b/raft/tracker/tracker.go
@@ -21,12 +21,27 @@ import (
 	"go.etcd.io/etcd/raft/quorum"
 )
 
+// A Config reflects the configuration tracked in a ProgressTracker.
+type Config struct {
+	Voters   quorum.JointConfig
+	Learners map[uint64]struct{}
+}
+
+func (c *Config) String() string {
+	if len(c.Learners) == 0 {
+		return fmt.Sprintf("voters=%s", c.Voters)
+	}
+	return fmt.Sprintf(
+		"voters=%s learners=%s",
+		c.Voters, quorum.MajorityConfig(c.Learners).String(),
+	)
+}
+
 // ProgressTracker tracks the currently active configuration and the information
 // known about the nodes and learners in it. In particular, it tracks the match
 // index for each peer which in turn allows reasoning about the committed index.
 type ProgressTracker struct {
-	Voters   quorum.JointConfig
-	Learners map[uint64]struct{}
+	Config
 
 	Progress map[uint64]*Progress
 
@@ -39,11 +54,15 @@ type ProgressTracker struct {
 func MakeProgressTracker(maxInflight int) ProgressTracker {
 	p := ProgressTracker{
 		MaxInflight: maxInflight,
-		Voters: quorum.JointConfig{
-			quorum.MajorityConfig{},
-			quorum.MajorityConfig{},
+		Config: Config{
+			Voters: quorum.JointConfig{
+				quorum.MajorityConfig{},
+				// TODO(tbg): this will be mostly empty, so make it a nil pointer
+				// in the common case.
+				quorum.MajorityConfig{},
+			},
+			Learners: map[uint64]struct{}{},
 		},
-		Learners: map[uint64]struct{}{},
 		Votes:    map[uint64]bool{},
 		Progress: map[uint64]*Progress{},
 	}