implement nopcache

cache.go

@@ -54,7 +54,7 @@ type Cache interface {
 	SetStats(s StatsClient)
 }
 
-// LRUCache represents a least recently used Cache implemenation.
+// LRUCache represents a least recently used Cache implementation.
 type LRUCache struct {
 	cache  *lru.Cache
 	counts map[uint64]uint64
@@ -483,3 +483,35 @@ func (s *SimpleCache) Fetch(id uint64) (*Bitmap, bool) {
 func (s *SimpleCache) Add(id uint64, b *Bitmap) {
 	s.cache[id] = b
 }
+
+type NopCache struct {
+	stats StatsClient
+}
+
+// NopCache implement Cache interface, returns no cache for cache type None
+var _ Cache = &NopCache{}
+
+// NewNopeCache returns a new instance of NopCache.
+func NewNopCache() *NopCache {
+	c := &NopCache{
+		stats: NopStatsClient,
+	}
+	return c
+}
+
+func (c *NopCache) Add(id uint64, n uint64)     {}
+func (c *NopCache) BulkAdd(id uint64, n uint64) {}
+func (c *NopCache) Get(id uint64) uint64 { return 0 }
+func (c *NopCache) IDs() []uint64 { return make([]uint64, 0, 0) }
+
+func (c *NopCache) Invalidate() {}
+func (c *NopCache) Len() int { return 0 }
+func (c *NopCache) Recalculate() {
+}
+func (c *NopCache) SetStats(s StatsClient) {
+	c.stats = s
+}
+
+func (c *NopCache) Top() []BitmapPair {
+	return []BitmapPair{}
+}

fragment.go

@@ -249,6 +249,8 @@ func (f *Fragment) openCache() error {
 		f.cache = NewRankCache(f.CacheSize)
 	case CacheTypeLRU:
 		f.cache = NewLRUCache(f.CacheSize)
+	case CacheTypeNone:
+		f.cache = NewNopCache()
 	default:
 		return ErrInvalidCacheType
 	}

frame.go

@@ -905,12 +905,13 @@ func (p importBitSet) Less(i, j int) bool { return p.rowIDs[i] < p.rowIDs[j] }
 const (
 	CacheTypeLRU    = "lru"
 	CacheTypeRanked = "ranked"
+	CacheTypeNone   = "none"
 )
 
 // IsValidCacheType returns true if v is a valid cache type.
 func IsValidCacheType(v string) bool {
 	switch v {
-	case CacheTypeLRU, CacheTypeRanked:
+	case CacheTypeLRU, CacheTypeRanked, CacheTypeNone:
 		return true
 	default:
 		return false