cs: update wal comments (#3334)

* cs: update wal comments

Follow-up to https://github.com/tendermint/tendermint/pull/3300

* Update consensus/wal.go

Co-Authored-By: melekes <anton.kalyaev@gmail.com>

consensus/wal.go

@@ -67,9 +67,10 @@ type WAL interface {
 }
 
 // Write ahead logger writes msgs to disk before they are processed.
-// Can be used for crash-recovery and deterministic replay
-// TODO: currently the wal is overwritten during replay catchup
-//   give it a mode so it's either reading or appending - must read to end to start appending again
+// Can be used for crash-recovery and deterministic replay.
+// TODO: currently the wal is overwritten during replay catchup, give it a mode
+// so it's either reading or appending - must read to end to start appending
+// again.
 type baseWAL struct {
 	cmn.BaseService
 
@@ -81,9 +82,8 @@ type baseWAL struct {
 	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.
+// NewWAL returns a new write-ahead logger based on `baseWAL`, which implements
+// WAL. It's flushed and synced to disk every 2s and once when stopped.
 func NewWAL(walFile string, groupOptions ...func(*auto.Group)) (*baseWAL, error) {
 	err := cmn.EnsureDir(filepath.Dir(walFile), 0700)
 	if err != nil {
@@ -130,13 +130,11 @@ func (wal *baseWAL) OnStart() error {
 	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 {
+			if err := wal.Flush(); err != nil {
 				wal.Logger.Error("Periodic WAL flush failed", "err", err)
 			}
 		case <-wal.Quit():
@@ -145,7 +143,7 @@ func (wal *baseWAL) processFlushTicks() {
 	}
 }
 
-// Flush will attempt to flush the underlying group's data to disk.
+// Flush will attempt to flush and fsync the underlying group's data to disk.
 func (wal *baseWAL) Flush() error {
 	return wal.group.Flush()
 }