Purge stale object cache entry (#2770)

cmd/xl-v1-object.go

@@ -121,7 +121,7 @@ func (xl xlObjects) GetObject(bucket, object string, startOffset int64, length i
 	if xlMeta.Stat.Size > 0 && xl.objCacheEnabled {
 		// Validate if we have previous cache.
 		var cachedBuffer io.ReadSeeker
-		cachedBuffer, err = xl.objCache.Open(path.Join(bucket, object))
+		cachedBuffer, err = xl.objCache.Open(path.Join(bucket, object), modTime)
 		if err == nil { // Cache hit.
 			// Advance the buffer to offset as if it was read.
 			if _, err = cachedBuffer.Seek(startOffset, 0); err != nil { // Seek to the offset.

pkg/objcache/objcache.go

@@ -163,7 +163,9 @@ func (c *Cache) Create(key string, size int64) (w io.WriteCloser, err error) {
 
 // Open - open the in-memory file, returns an in memory read seeker.
 // returns an error ErrNotFoundInCache, if the key does not exist.
-func (c *Cache) Open(key string) (io.ReadSeeker, error) {
+// Returns ErrKeyNotFoundInCache if entry's lastAccessedTime is older
+// than objModTime.
+func (c *Cache) Open(key string, objModTime time.Time) (io.ReadSeeker, error) {
 	// Entry exists, return the readable buffer.
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
@@ -171,6 +173,11 @@ func (c *Cache) Open(key string) (io.ReadSeeker, error) {
 	if !ok {
 		return nil, ErrKeyNotFoundInCache
 	}
+	// Check if buf is recent copy of the object on disk.
+	if buf.lastAccessed.Before(objModTime) {
+		c.delete(key)
+		return nil, ErrKeyNotFoundInCache
+	}
 	buf.lastAccessed = time.Now().UTC()
 	return bytes.NewReader(buf.value), nil
 }

pkg/objcache/objcache_test.go

@@ -57,7 +57,9 @@ func TestObjExpiry(t *testing.T) {
 	}
 	// Wait for 500 millisecond.
 	time.Sleep(500 * time.Millisecond)
-	_, err = cache.Open("test")
+	// Setting objModTime to the beginning of golang's time.Time to avoid deletion of stale entry.
+	fakeObjModTime := time.Time{}
+	_, err = cache.Open("test", fakeObjModTime)
 	if err != testCase.err {
 		t.Errorf("Test case 1 expected %s, got instead %s", testCase.err, err)
 	}
@@ -65,6 +67,9 @@ func TestObjExpiry(t *testing.T) {
 
 // TestObjCache - tests various cases for object cache behavior.
 func TestObjCache(t *testing.T) {
+	// Setting objModTime to the beginning of golang's time.Time to avoid deletion of stale entry.
+	fakeObjModTime := time.Time{}
+
 	// Non exhaustive list of all object cache behavior cases.
 	testCases := []struct {
 		expiry    time.Duration
@@ -117,7 +122,7 @@ func TestObjCache(t *testing.T) {
 	// Test 1 validating Open failure.
 	testCase := testCases[0]
 	cache := New(testCase.cacheSize, testCase.expiry)
-	_, err := cache.Open("test")
+	_, err := cache.Open("test", fakeObjModTime)
 	if testCase.err != err {
 		t.Errorf("Test case 2 expected to pass, failed instead %s", err)
 	}
@@ -157,7 +162,7 @@ func TestObjCache(t *testing.T) {
 	if err = w.Close(); err != nil {
 		t.Errorf("Test case 4 expected to pass, failed instead %s", err)
 	}
-	r, err := cache.Open("test")
+	r, err := cache.Open("test", fakeObjModTime)
 	if err != nil {
 		t.Errorf("Test case 4 expected to pass, failed instead %s", err)
 	}
@@ -186,7 +191,7 @@ func TestObjCache(t *testing.T) {
 	}
 	// Delete the cache entry.
 	cache.Delete("test")
-	_, err = cache.Open("test")
+	_, err = cache.Open("test", fakeObjModTime)
 	if testCase.err != err {
 		t.Errorf("Test case 5 expected to pass, failed instead %s", err)
 	}
@@ -237,3 +242,23 @@ func TestObjCache(t *testing.T) {
 		t.Errorf("Test case 7 expected to fail, passed instead")
 	}
 }
+
+// TestStateEntryPurge - tests if objCache purges stale entry and returns ErrKeyNotFoundInCache.
+func TestStaleEntryPurge(t *testing.T) {
+	cache := New(1024, NoExpiry)
+	w, err := cache.Create("test", 5)
+	if err != nil {
+		t.Errorf("Test case expected to pass, failed instead %s", err)
+	}
+	// Write '5' bytes.
+	w.Write([]byte("Hello"))
+	// Close to successfully save into cache.
+	if err = w.Close(); err != nil {
+		t.Errorf("Test case expected to pass, failed instead %s", err)
+	}
+
+	_, err = cache.Open("test", time.Now().AddDate(0, 0, 1).UTC())
+	if err != ErrKeyNotFoundInCache {
+		t.Errorf("Test case expected to return ErrKeyNotFoundInCache, instead returned %s", err)
+	}
+}