db: use Peek in TestVersionSetSeqNums

Adapt TestVersionSetSeqNums to use pebble.Peek to identify the current active
MANIFEST. Previously this unit test would use the last MANIFEST file returned
by the List call.

Additionally, on failure this test now logs the filesystem operations executed
during the test.

Author: jbowens

version_set_test.go

@@ -296,61 +296,70 @@ func TestVersionSetCheckpoint(t *testing.T) {
 }
 
 func TestVersionSetSeqNums(t *testing.T) {
-	mem := vfs.NewMem()
-	require.NoError(t, mem.MkdirAll("ext", 0755))
+	var buf struct {
+		sync.Mutex
+		bytes.Buffer
+	}
+	fs := vfs.WithLogging(vfs.NewMem(), func(format string, args ...interface{}) {
+		buf.Mutex.Lock()
+		defer buf.Mutex.Unlock()
+		fmt.Fprintf(&buf.Buffer, format, args...)
+		fmt.Fprintln(&buf)
+	})
+	defer func() {
+		if t.Failed() {
+			t.Logf("fs log:\n%s", buf.String())
+		}
+	}()
+	require.NoError(t, fs.MkdirAll("ext", 0755))
 
 	opts := &Options{
-		FS:                  mem,
+		FS:                  fs,
 		MaxManifestFileSize: 1,
 		Logger:              testutils.Logger{T: t},
 	}
 	d, err := Open("", opts)
 	require.NoError(t, err)
 
 	// Snapshot has no files, so first edit will cause manifest rotation.
-	writeAndIngest(t, mem, d, base.MakeInternalKey([]byte("a"), 0, InternalKeyKindSet), []byte("b"), "a")
+	writeAndIngest(t, fs, d, base.MakeInternalKey([]byte("a"), 0, InternalKeyKindSet), []byte("b"), "a")
 	// Snapshot has no files, and manifest has an edit from the previous ingest,
 	// so this second ingest will cause manifest rotation.
-	writeAndIngest(t, mem, d, base.MakeInternalKey([]byte("c"), 0, InternalKeyKindSet), []byte("d"), "c")
+	writeAndIngest(t, fs, d, base.MakeInternalKey([]byte("c"), 0, InternalKeyKindSet), []byte("d"), "c")
 	require.NoError(t, d.Close())
 	d, err = Open("", opts)
 	require.NoError(t, err)
 	defer d.Close()
 	d.TestOnlyWaitForCleaning()
 
-	// Check that the manifest has the correct LastSeqNum, equalling the highest
-	// observed SeqNum.
-	filenames, err := mem.List("")
+	// Check that the current manifest has the correct LastSeqNum, equalling the
+	// highest observed SeqNum.
+	desc, err := Peek("", fs)
 	require.NoError(t, err)
-	var manifestFile vfs.File
-	for _, filename := range filenames {
-		fileType, _, ok := base.ParseFilename(mem, filename)
-		if ok && fileType == base.FileTypeManifest {
-			manifestFile, err = mem.Open(filename)
-			require.NoError(t, err)
-		}
-	}
-	require.NotNil(t, manifestFile)
-	defer manifestFile.Close()
-	rr := record.NewReader(manifestFile, 0 /* logNum */)
-	var lastSeqNum base.SeqNum
-	for {
-		r, err := rr.Next()
-		if err == io.EOF {
-			break
-		}
-		require.NoError(t, err)
-		var ve manifest.VersionEdit
-		err = ve.Decode(r)
+	require.True(t, desc.Exists)
+	func() {
+		manifestFile, err := fs.Open(desc.ManifestFilename)
 		require.NoError(t, err)
-		if ve.LastSeqNum != 0 {
-			lastSeqNum = ve.LastSeqNum
+		defer manifestFile.Close()
+		rr := record.NewReader(manifestFile, 0 /* logNum */)
+		var lastSeqNum base.SeqNum
+		for {
+			r, err := rr.Next()
+			if err == io.EOF {
+				break
+			}
+			require.NoError(t, err)
+			var ve manifest.VersionEdit
+			require.NoError(t, ve.Decode(r))
+			if ve.LastSeqNum != 0 {
+				lastSeqNum = ve.LastSeqNum
+			}
 		}
-	}
-	// 2 ingestions happened, so LastSeqNum should equal base.SeqNumStart + 1.
-	require.Equal(t, base.SeqNum(11), lastSeqNum)
-	// logSeqNum is always one greater than the last assigned sequence number.
-	require.Equal(t, d.mu.versions.logSeqNum.Load(), lastSeqNum+1)
+		// 2 ingestions happened, so LastSeqNum should equal base.SeqNumStart + 1.
+		require.Equal(t, base.SeqNum(11), lastSeqNum)
+		// logSeqNum is always one greater than the last assigned sequence number.
+		require.Equal(t, d.mu.versions.logSeqNum.Load(), lastSeqNum+1)
+	}()
 }
 
 // TestLargeKeys is a datadriven test that exercises large keys with shared