Repository: prometheus/tsdb (go)

Issue:
Ability to create db with NopWAL
We create a test db in prometheus for unit-testing and general tests. Ideally we never write anything to disk there but turns out we do because we cannot disable the WAL.

Pull request description:
Added ability to create db with NopWal
Closes #452 

Signed-off-by: Vishnunarayan K I <appukuttancr@gmail.com>

Patch:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index f7dbb7b..51858f3 100644
--- a/CHANGELOG.md
+++ b/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)
@@ -15,7 +16,7 @@
    - Added `MergeOverlappingChunks` function in `chunks/chunks.go` to merge multiple time-overlapping Chunk Metas.
    - Added `MinTime` and `MaxTime` method for `BlockReader`.
  - [FEATURE] New `dump` command to tsdb tool to dump all samples.
- - [FEATURE] New `encoding` package for common binary encoding/decoding helpers. 
+ - [FEATURE] New `encoding` package for common binary encoding/decoding helpers.
     - Added to remove some code duplication.
  - [ENHANCEMENT] When closing the db any running compaction will be cancelled so it doesn't block.
    - `NewLeveledCompactor` takes a context.
@@ -41,7 +42,7 @@
  - [CHANGE] `LastCheckpoint()` used to return just the segment name and now it returns the full relative path.
  - [CHANGE] `NewSegmentsRangeReader()` can now read over miltiple wal ranges by using the new `SegmentRange{}` struct.
  - [CHANGE] `CorruptionErr{}` now also exposes the Segment `Dir` which is added when displaying any errors.
- - [CHANGE] `Head.Init()` is changed to `Head.Init(minValidTime int64)`  
+ - [CHANGE] `Head.Init()` is changed to `Head.Init(minValidTime int64)`
  - [CHANGE] `SymbolTable()` renamed to `SymbolTableSize()` to make the name consistent with the  `Block{ symbolTableSize uint64 }` field.
  - [CHANGE] `wal.Reader{}` now exposes `Segment()` for the current segment being read  and `Offset()` for the current offset.
  - [FEATURE] tsdbutil analyze subcomand to find churn, high cardinality, etc.
diff --git a/db.go b/db.go
index a3230ea..80f8deb 100644
--- a/db.go
+++ b/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
-	if opts.WALSegmentSize > 0 {
-		segmentSize = opts.WALSegmentSize
-	}
-	wlog, err := wal.NewSize(l, r, filepath.Join(dir, "wal"), segmentSize)
-	if err != nil {
-		return nil, err
+	// 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)
+		if err != nil {
+			return nil, err
+		}
 	}
+
 	db.head, err = NewHead(r, l, wlog, opts.BlockRanges[0])
 	if err != nil {
 		return nil, err


Test patch:
diff --git a/db_test.go b/db_test.go
index 26325d5..3d6aa6a 100644
--- a/db_test.go
+++ b/db_test.go
@@ -746,29 +746,53 @@ func TestWALFlushedOnDBClose(t *testing.T) {
 	testutil.Equals(t, []string{"labelvalue"}, values)
 }
 
-func TestWALSegmentSizeOption(t *testing.T) {
-	options := *DefaultOptions
-	options.WALSegmentSize = 2 * 32 * 1024
-	db, delete := openTestDB(t, &options)
-	defer delete()
-	app := db.Appender()
-	for i := int64(0); i < 155; i++ {
-		_, err := app.Add(labels.Labels{labels.Label{Name: "wal", Value: "size"}}, i, rand.Float64())
-		testutil.Ok(t, err)
-		testutil.Ok(t, app.Commit())
+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 = segmentSize
+			db, delete := openTestDB(t, &options)
+			defer delete()
+			app := db.Appender()
+			for i := int64(0); i < 155; i++ {
+				_, err := app.Add(labels.Labels{labels.Label{Name: "wal", Value: "size"}}, i, rand.Float64())
+				testutil.Ok(t, err)
+				testutil.Ok(t, app.Commit())
+			}
 
-	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())
+			dbDir := db.Dir()
+			db.Close()
+			testFunc(dbDir, options.WALSegmentSize)
+		})
 	}
 }
 
@@ -1500,7 +1524,7 @@ func TestNoEmptyBlocks(t *testing.T) {
 		testutil.Assert(t, len(actBlocks) == 1, "No blocks created when compacting with >0 samples")
 	})
 
-	t.Run(`When no new block is created from head, and there are some blocks on disk 
+	t.Run(`When no new block is created from head, and there are some blocks on disk
 	compaction should not run into infinite loop (was seen during development).`, func(t *testing.T) {
 		oldBlocks := db.Blocks()
 		app := db.Appender()