cs: sync WAL more frequently (#3300)

As per #3043, this adds a ticker to sync the WAL every 2s while the WAL is running.

* Flush WAL every 2s

This adds a ticker that flushes the WAL every 2s while the WAL is
running. This is related to #3043.

* Fix spelling

* Increase timeout to 2mins for slower build environments

* Make WAL sync interval configurable

* Add TODO to replace testChan with more comprehensive testBus

* Remove extraneous debug statement

* Remove testChan in favour of using system time

As per
https://github.com/tendermint/tendermint/pull/3300#discussion_r255886586,
this removes the `testChan` WAL member and replaces the approach with a
system time-oriented one. In this new approach, we keep track of the
system time at which each flush and periodic flush successfully
occurred.

The naming of the various functions is also updated here to be more
consistent with "flushing" as opposed to "sync'ing".

* Update naming convention and ensure lock for timestamp update

* Add Flush method as part of WAL interface

Adds a `Flush` method as part of the WAL interface to enforce the idea
that we can manually trigger a WAL flush from outside of the WAL. This
is employed in the consensus state management to flush the WAL prior to
signing votes/proposals, as per https://github.com/tendermint/tendermint/issues/3043#issuecomment-453853630

* Update CHANGELOG_PENDING

* Remove mutex approach and replace with DI

The dependency injection approach to dealing with testing concerns could
allow similar effects to some kind of "testing bus"-based approach. This
commit introduces an example of this, where instead of relying on
(potentially fragile) timing of things between the code and the test, we
inject code into the function under test that can signal the test
through a channel.

This allows us to avoid the `time.Sleep()`-based approach previously
employed.

* Update comment on WAL flushing during vote signing

Co-Authored-By: thanethomson <connect@thanethomson.com>

* Simplify flush interval definition

Co-Authored-By: thanethomson <connect@thanethomson.com>

* Expand commentary on WAL disk flushing

Co-Authored-By: thanethomson <connect@thanethomson.com>

* Add broken test to illustrate WAL sync test problem

Removes test-related state (dependency injection code) from the WAL data
structure and adds test code to illustrate the problem with using
`WALGenerateNBlocks` and `wal.SearchForEndHeight` to test periodic
sync'ing.

* Fix test error messages

* Use WAL group buffer size to check for flush

A function is added to `libs/autofile/group.go#Group` in order to return
the size of the buffered data (i.e. data that has not yet been flushed
to disk). The test now checks that, prior to a `time.Sleep`, the group
buffer has data in it. After the `time.Sleep` (during which time the
periodic flush should have been called), the buffer should be empty.

* Remove config root dir removal from #3291

* Add godoc for NewWAL mentioning periodic sync

consensus/replay_test.go

@@ -83,7 +83,7 @@ func startNewConsensusStateAndWaitForBlock(t *testing.T, consensusReplayConfig *
 	require.NoError(t, err)
 	select {
 	case <-newBlockCh:
-	case <-time.After(60 * time.Second):
+	case <-time.After(120 * time.Second):
 		t.Fatalf("Timed out waiting for new block (see trace above)")
 	}
 }
@@ -128,8 +128,8 @@ func TestWALCrash(t *testing.T) {
 
 func crashWALandCheckLiveness(t *testing.T, consensusReplayConfig *cfg.Config,
 	initFn func(dbm.DB, *ConsensusState, context.Context), heightToStop int64) {
-	walPaniced := make(chan error)
-	crashingWal := &crashingWAL{panicCh: walPaniced, heightToStop: heightToStop}
+	walPanicked := make(chan error)
+	crashingWal := &crashingWAL{panicCh: walPanicked, heightToStop: heightToStop}
 
 	i := 1
 LOOP:
@@ -168,8 +168,8 @@ LOOP:
 		i++
 
 		select {
-		case err := <-walPaniced:
-			t.Logf("WAL paniced: %v", err)
+		case err := <-walPanicked:
+			t.Logf("WAL panicked: %v", err)
 
 			// make sure we can make blocks after a crash
 			startNewConsensusStateAndWaitForBlock(t, consensusReplayConfig, cs.Height, blockDB, stateDB)
@@ -190,14 +190,14 @@ LOOP:
 
 // crashingWAL is a WAL which crashes or rather simulates a crash during Save
 // (before and after). It remembers a message for which we last panicked
-// (lastPanicedForMsgIndex), so we don't panic for it in subsequent iterations.
+// (lastPanickedForMsgIndex), so we don't panic for it in subsequent iterations.
 type crashingWAL struct {
 	next         WAL
 	panicCh      chan error
 	heightToStop int64
 
-	msgIndex               int // current message index
-	lastPanicedForMsgIndex int // last message for which we panicked
+	msgIndex                int // current message index
+	lastPanickedForMsgIndex int // last message for which we panicked
 }
 
 // WALWriteError indicates a WAL crash.
@@ -232,8 +232,8 @@ func (w *crashingWAL) Write(m WALMessage) {
 		return
 	}
 
-	if w.msgIndex > w.lastPanicedForMsgIndex {
-		w.lastPanicedForMsgIndex = w.msgIndex
+	if w.msgIndex > w.lastPanickedForMsgIndex {
+		w.lastPanickedForMsgIndex = w.msgIndex
 		_, file, line, _ := runtime.Caller(1)
 		w.panicCh <- WALWriteError{fmt.Sprintf("failed to write %T to WAL (fileline: %s:%d)", m, file, line)}
 		runtime.Goexit()
@@ -255,6 +255,7 @@ func (w *crashingWAL) SearchForEndHeight(height int64, options *WALSearchOptions
 func (w *crashingWAL) Start() error { return w.next.Start() }
 func (w *crashingWAL) Stop() error  { return w.next.Stop() }
 func (w *crashingWAL) Wait()        { w.next.Wait() }
+func (w *crashingWAL) Flush() error { return w.Group().Flush() }
 
 //------------------------------------------------------------------------------------------
 // Handshake Tests

consensus/state.go

@@ -909,6 +909,9 @@ func (cs *ConsensusState) defaultDecideProposal(height int64, round int) {
 		}
 	}
 
+	// Flush the WAL. Otherwise, we may not recompute the same proposal to sign, and the privValidator will refuse to sign anything.
+	cs.wal.Flush()
+
 	// Make proposal
 	propBlockId := types.BlockID{Hash: block.Hash(), PartsHeader: blockParts.Header()}
 	proposal := types.NewProposal(height, round, cs.ValidRound, propBlockId)
@@ -1674,6 +1677,9 @@ func (cs *ConsensusState) addVote(vote *types.Vote, peerID p2p.ID) (added bool,
 }
 
 func (cs *ConsensusState) signVote(type_ types.SignedMsgType, hash []byte, header types.PartSetHeader) (*types.Vote, error) {
+	// Flush the WAL. Otherwise, we may not recompute the same vote to sign, and the privValidator will refuse to sign anything.
+	cs.wal.Flush()
+
 	addr := cs.privValidator.GetPubKey().Address()
 	valIndex, _ := cs.Validators.GetByAddress(addr)
 

consensus/wal.go

@@ -21,6 +21,9 @@ import (
 const (
 	// must be greater than types.BlockPartSizeBytes + a few bytes
 	maxMsgSizeBytes = 1024 * 1024 // 1MB
+
+	// how often the WAL should be sync'd during period sync'ing
+	walDefaultFlushInterval = 2 * time.Second
 )
 
 //--------------------------------------------------------
@@ -56,6 +59,7 @@ type WAL interface {
 	WriteSync(WALMessage)
 	Group() *auto.Group
 	SearchForEndHeight(height int64, options *WALSearchOptions) (gr *auto.GroupReader, found bool, err error)
+	Flush() error
 
 	Start() error
 	Stop() error
@@ -72,8 +76,14 @@ type baseWAL struct {
 	group *auto.Group
 
 	enc *WALEncoder
+
+	flushTicker   *time.Ticker
+	flushInterval time.Duration
 }
 
+// NewWAL attempts to create a new write-ahead logger based on `baseWAL`, which
+// implements all of the required WAL functionality. This base WAL also flushes
+// data to disk every 2s.
 func NewWAL(walFile string, groupOptions ...func(*auto.Group)) (*baseWAL, error) {
 	err := cmn.EnsureDir(filepath.Dir(walFile), 0700)
 	if err != nil {
@@ -85,13 +95,19 @@ func NewWAL(walFile string, groupOptions ...func(*auto.Group)) (*baseWAL, error)
 		return nil, err
 	}
 	wal := &baseWAL{
-		group: group,
-		enc:   NewWALEncoder(group),
+		group:         group,
+		enc:           NewWALEncoder(group),
+		flushInterval: walDefaultFlushInterval,
 	}
 	wal.BaseService = *cmn.NewBaseService(nil, "baseWAL", wal)
 	return wal, nil
 }
 
+// SetFlushInterval allows us to override the periodic flush interval for the WAL.
+func (wal *baseWAL) SetFlushInterval(i time.Duration) {
+	wal.flushInterval = i
+}
+
 func (wal *baseWAL) Group() *auto.Group {
 	return wal.group
 }
@@ -109,14 +125,37 @@ func (wal *baseWAL) OnStart() error {
 		wal.WriteSync(EndHeightMessage{0})
 	}
 	err = wal.group.Start()
+	wal.flushTicker = time.NewTicker(wal.flushInterval)
+	go wal.processFlushTicks()
 	return err
 }
 
+// processFlushTicks allows us to periodically attempt to sync the WAL to disk.
+func (wal *baseWAL) processFlushTicks() {
+	for {
+		select {
+		case <-wal.flushTicker.C:
+			err := wal.Flush()
+			if err != nil {
+				wal.Logger.Error("Periodic WAL flush failed", "err", err)
+			}
+		case <-wal.Quit():
+			return
+		}
+	}
+}
+
+// Flush will attempt to flush the underlying group's data to disk.
+func (wal *baseWAL) Flush() error {
+	return wal.group.Flush()
+}
+
 // Stop the underlying autofile group.
 // Use Wait() to ensure it's finished shutting down
 // before cleaning up files.
 func (wal *baseWAL) OnStop() {
-	wal.group.Flush()
+	wal.flushTicker.Stop()
+	wal.Flush()
 	wal.group.Stop()
 	wal.group.Close()
 }
@@ -150,7 +189,7 @@ func (wal *baseWAL) WriteSync(msg WALMessage) {
 	}
 
 	wal.Write(msg)
-	if err := wal.group.Flush(); err != nil {
+	if err := wal.Flush(); err != nil {
 		panic(fmt.Sprintf("Error flushing consensus wal buf to file. Error: %v \n", err))
 	}
 }
@@ -343,3 +382,4 @@ func (nilWAL) SearchForEndHeight(height int64, options *WALSearchOptions) (gr *a
 func (nilWAL) Start() error { return nil }
 func (nilWAL) Stop() error  { return nil }
 func (nilWAL) Wait()        {}
+func (nilWAL) Flush() error { return nil }

consensus/wal_generator.go

@@ -5,7 +5,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"os"
 	"path/filepath"
 	"testing"
 	"time"
@@ -24,13 +23,12 @@ import (
 	"github.com/tendermint/tendermint/types"
 )
 
-// WALGenerateNBlocks generates a consensus WAL. It does this by spining up a
+// WALGenerateNBlocks generates a consensus WAL. It does this by spinning up a
 // stripped down version of node (proxy app, event bus, consensus state) with a
 // persistent kvstore application and special consensus wal instance
 // (byteBufferWAL) and waits until numBlocks are created. If the node fails to produce given numBlocks, it returns an error.
 func WALGenerateNBlocks(t *testing.T, wr io.Writer, numBlocks int) (err error) {
 	config := getConfig(t)
-	defer os.RemoveAll(config.RootDir)
 
 	app := kvstore.NewPersistentKVStoreApplication(filepath.Join(config.DBDir(), "wal_generator"))
 
@@ -204,3 +202,4 @@ func (w *byteBufferWAL) SearchForEndHeight(height int64, options *WALSearchOptio
 func (w *byteBufferWAL) Start() error { return nil }
 func (w *byteBufferWAL) Stop() error  { return nil }
 func (w *byteBufferWAL) Wait()        {}
+func (w *byteBufferWAL) Flush() error { return nil }

consensus/wal_test.go

@@ -3,7 +3,6 @@ package consensus
 import (
 	"bytes"
 	"crypto/rand"
-	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -22,6 +21,10 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+const (
+	walTestFlushInterval = time.Duration(100) * time.Millisecond
+)
+
 func TestWALTruncate(t *testing.T) {
 	walDir, err := ioutil.TempDir("", "wal")
 	require.NoError(t, err)
@@ -57,9 +60,9 @@ func TestWALTruncate(t *testing.T) {
 
 	h := int64(50)
 	gr, found, err := wal.SearchForEndHeight(h, &WALSearchOptions{})
-	assert.NoError(t, err, fmt.Sprintf("expected not to err on height %d", h))
-	assert.True(t, found, fmt.Sprintf("expected to find end height for %d", h))
-	assert.NotNil(t, gr, "expected group not to be nil")
+	assert.NoError(t, err, "expected not to err on height %d", h)
+	assert.True(t, found, "expected to find end height for %d", h)
+	assert.NotNil(t, gr)
 	defer gr.Close()
 
 	dec := NewWALDecoder(gr)
@@ -67,7 +70,7 @@ func TestWALTruncate(t *testing.T) {
 	assert.NoError(t, err, "expected to decode a message")
 	rs, ok := msg.Msg.(tmtypes.EventDataRoundState)
 	assert.True(t, ok, "expected message of type EventDataRoundState")
-	assert.Equal(t, rs.Height, h+1, fmt.Sprintf("wrong height"))
+	assert.Equal(t, rs.Height, h+1, "wrong height")
 }
 
 func TestWALEncoderDecoder(t *testing.T) {
@@ -128,9 +131,9 @@ func TestWALSearchForEndHeight(t *testing.T) {
 
 	h := int64(3)
 	gr, found, err := wal.SearchForEndHeight(h, &WALSearchOptions{})
-	assert.NoError(t, err, fmt.Sprintf("expected not to err on height %d", h))
-	assert.True(t, found, fmt.Sprintf("expected to find end height for %d", h))
-	assert.NotNil(t, gr, "expected group not to be nil")
+	assert.NoError(t, err, "expected not to err on height %d", h)
+	assert.True(t, found, "expected to find end height for %d", h)
+	assert.NotNil(t, gr)
 	defer gr.Close()
 
 	dec := NewWALDecoder(gr)
@@ -138,7 +141,46 @@ func TestWALSearchForEndHeight(t *testing.T) {
 	assert.NoError(t, err, "expected to decode a message")
 	rs, ok := msg.Msg.(tmtypes.EventDataRoundState)
 	assert.True(t, ok, "expected message of type EventDataRoundState")
-	assert.Equal(t, rs.Height, h+1, fmt.Sprintf("wrong height"))
+	assert.Equal(t, rs.Height, h+1, "wrong height")
+}
+
+func TestWALPeriodicSync(t *testing.T) {
+	walDir, err := ioutil.TempDir("", "wal")
+	require.NoError(t, err)
+	defer os.RemoveAll(walDir)
+
+	walFile := filepath.Join(walDir, "wal")
+	wal, err := NewWAL(walFile, autofile.GroupCheckDuration(1*time.Millisecond))
+	require.NoError(t, err)
+
+	wal.SetFlushInterval(walTestFlushInterval)
+	wal.SetLogger(log.TestingLogger())
+
+	require.NoError(t, wal.Start())
+	defer func() {
+		wal.Stop()
+		wal.Wait()
+	}()
+
+	err = WALGenerateNBlocks(t, wal.Group(), 5)
+	require.NoError(t, err)
+
+	// We should have data in the buffer now
+	assert.NotZero(t, wal.Group().Buffered())
+
+	time.Sleep(walTestFlushInterval + (10 * time.Millisecond))
+
+	// The data should have been flushed by the periodic sync
+	assert.Zero(t, wal.Group().Buffered())
+
+	h := int64(4)
+	gr, found, err := wal.SearchForEndHeight(h, &WALSearchOptions{})
+	assert.NoError(t, err, "expected not to err on height %d", h)
+	assert.True(t, found, "expected to find end height for %d", h)
+	assert.NotNil(t, gr)
+	if gr != nil {
+		gr.Close()
+	}
 }
 
 /*

libs/autofile/group.go

@@ -209,6 +209,13 @@ func (g *Group) WriteLine(line string) error {
 	return err
 }
 
+// Buffered returns the size of the currently buffered data.
+func (g *Group) Buffered() int {
+	g.mtx.Lock()
+	defer g.mtx.Unlock()
+	return g.headBuf.Buffered()
+}
+
 // Flush writes any buffered data to the underlying file and commits the
 // current content of the file to stable storage.
 func (g *Group) Flush() error {