Merge pull request #7573 from codesome/mmap-empty-files

Avoid empty mmap files by using .tmp files to write headers

tsdb/chunks/chunks.go

@@ -217,22 +217,35 @@ func (w *Writer) cut() error {
 	return nil
 }
 
-func cutSegmentFile(dirFile *os.File, magicNumber uint32, chunksFormat byte, allocSize int64) (headerSize int, newFile *os.File, seq int, err error) {
+func cutSegmentFile(dirFile *os.File, magicNumber uint32, chunksFormat byte, allocSize int64) (headerSize int, newFile *os.File, seq int, returnErr error) {
 	p, seq, err := nextSequenceFile(dirFile.Name())
 	if err != nil {
-		return 0, nil, 0, err
+		return 0, nil, 0, errors.Wrap(err, "next sequence file")
 	}
-	f, err := os.OpenFile(p, os.O_WRONLY|os.O_CREATE, 0666)
+	ptmp := p + ".tmp"
+	f, err := os.OpenFile(ptmp, os.O_WRONLY|os.O_CREATE, 0666)
 	if err != nil {
-		return 0, nil, 0, err
+		return 0, nil, 0, errors.Wrap(err, "open temp file")
 	}
+	defer func() {
+		if returnErr != nil {
+			var merr tsdb_errors.MultiError
+			merr.Add(returnErr)
+			if f != nil {
+				merr.Add(f.Close())
+			}
+			// Calling RemoveAll on a non-existent file does not return error.
+			merr.Add(os.RemoveAll(ptmp))
+			returnErr = merr.Err()
+		}
+	}()
 	if allocSize > 0 {
 		if err = fileutil.Preallocate(f, allocSize, true); err != nil {
-			return 0, nil, 0, err
+			return 0, nil, 0, errors.Wrap(err, "preallocate")
 		}
 	}
 	if err = dirFile.Sync(); err != nil {
-		return 0, nil, 0, err
+		return 0, nil, 0, errors.Wrap(err, "sync directory")
 	}
 
 	// Write header metadata for new file.
@@ -242,7 +255,24 @@ func cutSegmentFile(dirFile *os.File, magicNumber uint32, chunksFormat byte, all
 
 	n, err := f.Write(metab)
 	if err != nil {
-		return 0, nil, 0, err
+		return 0, nil, 0, errors.Wrap(err, "write header")
+	}
+	if err := f.Close(); err != nil {
+		return 0, nil, 0, errors.Wrap(err, "close temp file")
+	}
+	f = nil
+
+	if err := fileutil.Rename(ptmp, p); err != nil {
+		return 0, nil, 0, errors.Wrap(err, "replace file")
+	}
+
+	f, err = os.OpenFile(p, os.O_WRONLY, 0666)
+	if err != nil {
+		return 0, nil, 0, errors.Wrap(err, "open final file")
+	}
+	// Skip header for further writes.
+	if _, err := f.Seek(int64(n), 0); err != nil {
+		return 0, nil, 0, errors.Wrap(err, "seek in final file")
 	}
 	return n, f, seq, nil
 }

tsdb/fileutil/fileutil.go

@@ -125,19 +125,5 @@ func Replace(from, to string) error {
 		}
 	}
 
-	if err := os.Rename(from, to); err != nil {
-		return err
-	}
-
-	// Directory was renamed; sync parent dir to persist rename.
-	pdir, err := OpenDir(filepath.Dir(to))
-	if err != nil {
-		return err
-	}
-
-	if err = pdir.Sync(); err != nil {
-		pdir.Close()
-		return err
-	}
-	return pdir.Close()
+	return Rename(from, to)
 }