Added ability to create db with NopWal (#519)

Signed-off-by: Vishnunarayan K I <appukuttancr@gmail.com>

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## master / unreleased
  - [REMOVED] `chunks.NewReader` is removed as it wasn't used anywhere.
  - [REMOVED] `FromData` is considered unused so was removed.
+ - [FEATURE] Added option WALSegmentSize -1 to disable the WAL.
 
 ## 0.6.1
   - [BUGFIX] Update `last` after appending a non-overlapping chunk in `chunks.MergeOverlappingChunks`. [#539](https://github.com/prometheus/tsdb/pull/539)

db.go

@@ -54,7 +54,10 @@ var DefaultOptions = &Options{
 
 // Options of the DB storage.
 type Options struct {
-	// Segments (wal files) max size
+	// Segments (wal files) max size.
+	// WALSegmentSize = 0, segment size is default size.
+	// WALSegmentSize > 0, segment size is WALSegmentSize.
+	// WALSegmentSize < 0, wal is disabled.
 	WALSegmentSize int
 
 	// Duration of persisted data to keep.
@@ -288,14 +291,20 @@ func Open(dir string, l log.Logger, r prometheus.Registerer, opts *Options) (db
 	}
 	db.compactCancel = cancel
 
+	var wlog *wal.WAL
 	segmentSize := wal.DefaultSegmentSize
+	// Wal is enabled.
+	if opts.WALSegmentSize >= 0 {
+		// Wal is set to a custom size.
 		if opts.WALSegmentSize > 0 {
 			segmentSize = opts.WALSegmentSize
 		}
-	wlog, err := wal.NewSize(l, r, filepath.Join(dir, "wal"), segmentSize)
+		wlog, err = wal.NewSize(l, r, filepath.Join(dir, "wal"), segmentSize)
 		if err != nil {
 			return nil, err
 		}
+	}
+
 	db.head, err = NewHead(r, l, wlog, opts.BlockRanges[0])
 	if err != nil {
 		return nil, err

db_test.go

@@ -746,9 +746,40 @@ func TestWALFlushedOnDBClose(t *testing.T) {
 	testutil.Equals(t, []string{"labelvalue"}, values)
 }
 
-func TestWALSegmentSizeOption(t *testing.T) {
+func TestWALSegmentSizeOptions(t *testing.T) {
+	tests := map[int]func(dbdir string, segmentSize int){
+		// Default Wal Size.
+		0: func(dbDir string, segmentSize int) {
+			files, err := ioutil.ReadDir(filepath.Join(dbDir, "wal"))
+			testutil.Ok(t, err)
+			for _, f := range files[:len(files)-1] {
+				testutil.Equals(t, int64(DefaultOptions.WALSegmentSize), f.Size(), "WAL file size doesn't match WALSegmentSize option, filename: %v", f.Name())
+			}
+			lastFile := files[len(files)-1]
+			testutil.Assert(t, int64(DefaultOptions.WALSegmentSize) > lastFile.Size(), "last WAL file size is not smaller than the WALSegmentSize option, filename: %v", lastFile.Name())
+		},
+		// Custom Wal Size.
+		2 * 32 * 1024: func(dbDir string, segmentSize int) {
+			files, err := ioutil.ReadDir(filepath.Join(dbDir, "wal"))
+			testutil.Assert(t, len(files) > 1, "current WALSegmentSize should result in more than a single WAL file.")
+			testutil.Ok(t, err)
+			for _, f := range files[:len(files)-1] {
+				testutil.Equals(t, int64(segmentSize), f.Size(), "WAL file size doesn't match WALSegmentSize option, filename: %v", f.Name())
+			}
+			lastFile := files[len(files)-1]
+			testutil.Assert(t, int64(segmentSize) > lastFile.Size(), "last WAL file size is not smaller than the WALSegmentSize option, filename: %v", lastFile.Name())
+		},
+		// Wal disabled.
+		-1: func(dbDir string, segmentSize int) {
+			if _, err := os.Stat(filepath.Join(dbDir, "wal")); !os.IsNotExist(err) {
+				t.Fatal("wal directory is present when the wal is disabled")
+			}
+		},
+	}
+	for segmentSize, testFunc := range tests {
+		t.Run(fmt.Sprintf("WALSegmentSize %d test", segmentSize), func(t *testing.T) {
 			options := *DefaultOptions
-	options.WALSegmentSize = 2 * 32 * 1024
+			options.WALSegmentSize = segmentSize
 			db, delete := openTestDB(t, &options)
 			defer delete()
 			app := db.Appender()
@@ -760,15 +791,8 @@ func TestWALSegmentSizeOption(t *testing.T) {
 
 			dbDir := db.Dir()
 			db.Close()
-	files, err := ioutil.ReadDir(filepath.Join(dbDir, "wal"))
-	testutil.Assert(t, len(files) > 1, "current WALSegmentSize should result in more than a single WAL file.")
-	testutil.Ok(t, err)
-	for i, f := range files {
-		if len(files)-1 != i {
-			testutil.Equals(t, int64(options.WALSegmentSize), f.Size(), "WAL file size doesn't match WALSegmentSize option, filename: %v", f.Name())
-			continue
-		}
-		testutil.Assert(t, int64(options.WALSegmentSize) > f.Size(), "last WAL file size is not smaller than the WALSegmentSize option, filename: %v", f.Name())
+			testFunc(dbDir, options.WALSegmentSize)
+		})
 	}
 }