core/rawdb: fsync head data file before closing it (ethereum#26490)

This PR fixes an issue which might result in data lost in freezer.

Whenever mutation happens in freezer, all data will be written into head data file
and it will be rotated with a new one in case the size of file reaches the threshold.

Theoretically, the rotated old data file should be fsync'd to prevent data loss.
In freezer.Sync function, we only fsync: (1) index file (2) meta file and (3) head
data file. So this PR forcibly fsync the head data file if mutation happens in the
boundary of data file.

core/rawdb/chain_freezer.go

@@ -86,14 +86,14 @@ func (f *chainFreezer) Close() error {
 // This functionality is deliberately broken off from block importing to avoid
 // incurring additional data shuffling delays on block propagation.
 func (f *chainFreezer) freeze(db ethdb.KeyValueStore) {
-	nfdb := &nofreezedb{KeyValueStore: db}
-
 	var (
 		backoff   bool
 		triggered chan struct{} // Used in tests
+		nfdb      = &nofreezedb{KeyValueStore: db}
 	)
 	timer := time.NewTimer(freezerRecheckInterval)
 	defer timer.Stop()
+
 	for {
 		select {
 		case <-f.quit:

core/rawdb/freezer_table.go

@@ -852,8 +852,11 @@ func (t *freezerTable) advanceHead() error {
 	if err != nil {
 		return err
 	}
-
-	// Close old file, and reopen in RDONLY mode.
+	// Commit the contents of the old file to stable storage and
+	// tear it down. It will be re-opened in read-only mode.
+	if err := t.head.Sync(); err != nil {
+		return err
+	}
 	t.releaseFile(t.headId)
 	t.openFile(t.headId, openFreezerFileForReadOnly)
 

core/rawdb/freezer_test.go

@@ -190,7 +190,7 @@ func TestFreezerConcurrentModifyTruncate(t *testing.T) {
 
 	var item = make([]byte, 256)
 
-	for i := 0; i < 1000; i++ {
+	for i := 0; i < 10; i++ {
 		// First reset and write 100 items.
 		if err := f.TruncateHead(0); err != nil {
 			t.Fatal("truncate failed:", err)