raft: Garbage collect WAL files

We currently garbage collect snapshot files (keeping only
KeepOldSnapshot outdated snapshots, which defaults to 0). However, we
don't garbage collect the WAL files that the snapshots replace.

Delete any WALs which are so old that they only contain information that
predates the oldest of the snapshots we have retained. This means that
by default, we will remove old WALs once they are supplanted by a
snapshot. However, if KeepOldSnapshots is set above 0, we will keep
whichever WALs are necessary to catch up from the oldest of the retained
snapshots. This makes sure that the old snapshots we retain are actually
useful, and avoids adding an independent knob for WAL retention that
might end up with an inconsistent setting.

Also, fix serious brokenness in the the deletion of old snapshots (it
was deleting the most recent outdated snapshots, instead of the oldest).

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

Author: Aaron Lehmann

manager/state/raft/storage.go

@@ -10,6 +10,7 @@ import (
 	"sort"
 	"strings"
 
+	"github.com/coreos/etcd/pkg/fileutil"
 	"github.com/coreos/etcd/raft"
 	"github.com/coreos/etcd/raft/raftpb"
 	"github.com/coreos/etcd/snap"
@@ -80,7 +81,7 @@ func (n *Node) createWAL(nodeID string) (raft.Peer, error) {
 	}
 	n.wal, err = wal.Create(n.walDir(), metadata)
 	if err != nil {
-		return raft.Peer{}, fmt.Errorf("create wal error: %v", err)
+		return raft.Peer{}, fmt.Errorf("create WAL error: %v", err)
 	}
 
 	n.cluster.AddMember(&membership.Member{RaftMember: raftNode})
@@ -127,15 +128,15 @@ func (n *Node) readWAL(ctx context.Context, snapshot *raftpb.Snapshot, forceNewC
 	repaired := false
 	for {
 		if n.wal, err = wal.Open(n.walDir(), walsnap); err != nil {
-			return fmt.Errorf("open wal error: %v", err)
+			return fmt.Errorf("open WAL error: %v", err)
 		}
 		if metadata, st, ents, err = n.wal.ReadAll(); err != nil {
 			if err := n.wal.Close(); err != nil {
 				return err
 			}
 			// we can only repair ErrUnexpectedEOF and we never repair twice.
 			if repaired || err != io.ErrUnexpectedEOF {
-				return fmt.Errorf("read wal error (%v) and cannot be repaired", err)
+				return fmt.Errorf("read WAL error (%v) and cannot be repaired", err)
 			}
 			if !wal.Repair(n.walDir()) {
 				return fmt.Errorf("WAL error (%v) cannot be repaired", err)
@@ -157,7 +158,7 @@ func (n *Node) readWAL(ctx context.Context, snapshot *raftpb.Snapshot, forceNewC
 
 	var raftNode api.RaftMember
 	if err := raftNode.Unmarshal(metadata); err != nil {
-		return fmt.Errorf("error unmarshalling wal metadata: %v", err)
+		return fmt.Errorf("error unmarshalling WAL metadata: %v", err)
 	}
 	n.Config.ID = raftNode.RaftID
 
@@ -274,25 +275,106 @@ func (n *Node) saveSnapshot(snapshot raftpb.Snapshot, keepOldSnapshots uint64) e
 	// This means that if the current snapshot doesn't appear in the
 	// directory for some strange reason, we won't delete anything, which
 	// is the safe behavior.
+	curSnapshotIdx := -1
 	var (
-		afterCurSnapshot bool
-		removeErr        error
+		removeErr          error
+		remainingSnapshots []string
 	)
+
 	for i, snapFile := range snapshots {
-		if afterCurSnapshot {
-			if uint64(len(snapshots)-i) <= keepOldSnapshots {
-				return removeErr
-			}
-			err := os.Remove(filepath.Join(n.snapDir(), snapFile))
-			if err != nil && removeErr == nil {
-				removeErr = err
+		if curSnapshotIdx >= 0 && i > curSnapshotIdx {
+			if uint64(i-curSnapshotIdx) > keepOldSnapshots {
+				err := os.Remove(filepath.Join(n.snapDir(), snapFile))
+				if err != nil && removeErr == nil {
+					removeErr = err
+				}
+				continue
 			}
 		} else if snapFile == curSnapshot {
-			afterCurSnapshot = true
+			curSnapshotIdx = i
+		}
+		remainingSnapshots = append(remainingSnapshots, snapFile)
+	}
+
+	if removeErr != nil {
+		return removeErr
+	}
+
+	// Remove any WAL files that only contain data from before the oldest
+	// remaining snapshot.
+
+	if len(remainingSnapshots) == 0 {
+		return nil
+	}
+
+	// Sort snapshot filenames in lexical order
+	sort.Sort(sort.StringSlice(remainingSnapshots))
+
+	// Parse index out of snapshot filename
+	var snapTerm, snapIndex uint64
+	_, err = fmt.Sscanf(remainingSnapshots[0], "%016x-%016x.snap", &snapTerm, &snapIndex)
+	if err != nil {
+		return fmt.Errorf("malformed snapshot filename %s: %v", remainingSnapshots[0], err)
+	}
+
+	// List the WALs
+	dirents, err = ioutil.ReadDir(n.walDir())
+	if err != nil {
+		return err
+	}
+
+	var wals []string
+	for _, dirent := range dirents {
+		if strings.HasSuffix(dirent.Name(), ".wal") {
+			wals = append(wals, dirent.Name())
 		}
 	}
 
-	return removeErr
+	// Sort WAL filenames in lexical order
+	sort.Sort(sort.StringSlice(wals))
+
+	found := false
+	deleteUntil := -1
+
+	for i, walName := range wals {
+		var walSeq, walIndex uint64
+		_, err = fmt.Sscanf(walName, "%016x-%016x.wal", &walSeq, &walIndex)
+		if err != nil {
+			return fmt.Errorf("could not parse WAL name %s: %v", walName, err)
+		}
+
+		if walIndex >= snapIndex {
+			deleteUntil = i - 1
+			found = true
+			break
+		}
+	}
+
+	// If all WAL files started with indices below the oldest snapshot's
+	// index, we can delete all but the newest WAL file.
+	if !found && len(wals) != 0 {
+		deleteUntil = len(wals) - 1
+	}
+
+	for i := 0; i < deleteUntil; i++ {
+		walPath := filepath.Join(n.walDir(), wals[i])
+		l, err := fileutil.NewLock(walPath)
+		if err != nil {
+			continue
+		}
+		err = l.TryLock()
+		if err != nil {
+			return fmt.Errorf("could not lock old WAL file %s for removal: %v", wals[i], err)
+		}
+		err = os.Remove(walPath)
+		l.Unlock()
+		l.Destroy()
+		if err != nil {
+			return fmt.Errorf("error removing old WAL file %s: %v", wals[i], err)
+		}
+	}
+
+	return nil
 }
 
 func (n *Node) doSnapshot(raftConfig *api.RaftConfig) {

manager/state/raft/storage_test.go

@@ -5,11 +5,14 @@ import (
 	"io/ioutil"
 	"path/filepath"
 	"testing"
+	"time"
 
 	"github.com/docker/swarmkit/api"
 	raftutils "github.com/docker/swarmkit/manager/state/raft/testutils"
+	"github.com/docker/swarmkit/manager/state/store"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"golang.org/x/net/context"
 )
 
 func TestRaftSnapshot(t *testing.T) {
@@ -243,3 +246,180 @@ func TestRaftSnapshotRestart(t *testing.T) {
 	require.NoError(t, err)
 	raftutils.CheckValuesOnNodes(t, clockSource, nodes, nodeIDs, values)
 }
+
+func TestGCWAL(t *testing.T) {
+	if testing.Short() {
+		t.Skip("TestGCWAL skipped with -short because it's resource-intensive")
+	}
+	t.Parallel()
+
+	// Additional log entries from cluster setup, leader election
+	extraLogEntries := 5
+	// Number of large entries to propose
+	proposals := 47
+
+	// Bring up a 3 node cluster
+	nodes, clockSource := raftutils.NewRaftCluster(t, tc, &api.RaftConfig{SnapshotInterval: uint64(proposals + extraLogEntries), LogEntriesForSlowFollowers: 0})
+
+	for i := 0; i != proposals; i++ {
+		_, err := proposeHugeValue(t, nodes[1], DefaultProposalTime, fmt.Sprintf("id%d", i))
+		assert.NoError(t, err, "failed to propose value")
+	}
+
+	time.Sleep(250 * time.Millisecond)
+
+	// Snapshot should have been triggered just before the WAL rotated, so
+	// both WAL files should be preserved
+	assert.NoError(t, raftutils.PollFunc(clockSource, func() error {
+		dirents, err := ioutil.ReadDir(filepath.Join(nodes[1].StateDir, "snap"))
+		if err != nil {
+			return err
+		}
+		if len(dirents) != 1 {
+			return fmt.Errorf("expected 1 snapshot, found %d", len(dirents))
+		}
+
+		dirents, err = ioutil.ReadDir(filepath.Join(nodes[1].StateDir, "wal"))
+		if err != nil {
+			return err
+		}
+		if len(dirents) != 2 {
+			return fmt.Errorf("expected 2 WAL files, found %d", len(dirents))
+		}
+		return nil
+	}))
+
+	raftutils.TeardownCluster(t, nodes)
+
+	// Repeat this test, but trigger the snapshot after the WAL has rotated
+	proposals++
+	nodes, clockSource = raftutils.NewRaftCluster(t, tc, &api.RaftConfig{SnapshotInterval: uint64(proposals + extraLogEntries), LogEntriesForSlowFollowers: 0})
+	defer raftutils.TeardownCluster(t, nodes)
+
+	for i := 0; i != proposals; i++ {
+		_, err := proposeHugeValue(t, nodes[1], DefaultProposalTime, fmt.Sprintf("id%d", i))
+		assert.NoError(t, err, "failed to propose value")
+	}
+
+	time.Sleep(250 * time.Millisecond)
+
+	// This time only one WAL file should be saved.
+	assert.NoError(t, raftutils.PollFunc(clockSource, func() error {
+		dirents, err := ioutil.ReadDir(filepath.Join(nodes[1].StateDir, "snap"))
+		if err != nil {
+			return err
+		}
+		if len(dirents) != 1 {
+			return fmt.Errorf("expected 1 snapshot, found %d", len(dirents))
+		}
+
+		dirents, err = ioutil.ReadDir(filepath.Join(nodes[1].StateDir, "wal"))
+		if err != nil {
+			return err
+		}
+		if len(dirents) != 1 {
+			return fmt.Errorf("expected 1 WAL file, found %d", len(dirents))
+		}
+		return nil
+	}))
+
+	// Restart the whole cluster
+	for _, node := range nodes {
+		node.Server.Stop()
+		node.Shutdown()
+	}
+
+	raftutils.AdvanceTicks(clockSource, 5)
+
+	i := 0
+	for k, node := range nodes {
+		nodes[k] = raftutils.RestartNode(t, clockSource, node, false)
+		i++
+	}
+	raftutils.WaitForCluster(t, clockSource, nodes)
+
+	// Is the data intact after restart?
+	for _, node := range nodes {
+		assert.NoError(t, raftutils.PollFunc(clockSource, func() error {
+			var err error
+			node.MemoryStore().View(func(tx store.ReadTx) {
+				var allNodes []*api.Node
+				allNodes, err = store.FindNodes(tx, store.All)
+				if err != nil {
+					return
+				}
+				if len(allNodes) != proposals {
+					err = fmt.Errorf("expected %d nodes, got %d", proposals, len(allNodes))
+					return
+				}
+			})
+			return err
+		}))
+	}
+
+	// It should still be possible to propose values
+	_, err := raftutils.ProposeValue(t, raftutils.Leader(nodes), DefaultProposalTime, "newnode")
+	assert.NoError(t, err, "failed to propose value")
+
+	for _, node := range nodes {
+		assert.NoError(t, raftutils.PollFunc(clockSource, func() error {
+			var err error
+			node.MemoryStore().View(func(tx store.ReadTx) {
+				var allNodes []*api.Node
+				allNodes, err = store.FindNodes(tx, store.All)
+				if err != nil {
+					return
+				}
+				if len(allNodes) != proposals+1 {
+					err = fmt.Errorf("expected %d nodes, got %d", proposals, len(allNodes))
+					return
+				}
+			})
+			return err
+		}))
+	}
+}
+
+// proposeHugeValue proposes a 1.4MB value to a raft test cluster
+func proposeHugeValue(t *testing.T, raftNode *raftutils.TestNode, time time.Duration, nodeID ...string) (*api.Node, error) {
+	nodeIDStr := "id1"
+	if len(nodeID) != 0 {
+		nodeIDStr = nodeID[0]
+	}
+	a := make([]byte, 1400000)
+	for i := 0; i != len(a); i++ {
+		a[i] = 'a'
+	}
+	node := &api.Node{
+		ID: nodeIDStr,
+		Spec: api.NodeSpec{
+			Annotations: api.Annotations{
+				Name: nodeIDStr,
+				Labels: map[string]string{
+					"largestring": string(a),
+				},
+			},
+		},
+	}
+
+	storeActions := []*api.StoreAction{
+		{
+			Action: api.StoreActionKindCreate,
+			Target: &api.StoreAction_Node{
+				Node: node,
+			},
+		},
+	}
+
+	ctx, _ := context.WithTimeout(context.Background(), time)
+
+	err := raftNode.ProposeValue(ctx, storeActions, func() {
+		err := raftNode.MemoryStore().ApplyStoreActions(storeActions)
+		assert.NoError(t, err, "error applying actions")
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return node, nil
+}