Update cache to address PR comments

tsdb/engine/tsm1/cache.go

@@ -58,8 +58,8 @@ type Cache struct {
 	// flushingCaches are the cache objects that are currently being written to tsm files
 	// they're kept in memory while flushing so they can be queried along with the cache.
 	// they are read only and should never be modified
-	flushingCaches     []*Cache
-	flushingCachesSize uint64
+	snapshotCaches     []*Cache
+	snapshotCachesSize uint64
 }
 
 // NewCache returns an instance of a cache which will use a maximum of maxSize bytes of memory.
@@ -78,7 +78,7 @@ func (c *Cache) Write(key string, values []Value) error {
 
 	// Enough room in the cache?
 	newSize := c.size + uint64(Values(values).Size())
-	if c.maxSize > 0 && newSize+c.flushingCachesSize > c.maxSize {
+	if c.maxSize > 0 && newSize+c.snapshotCachesSize > c.maxSize {
 		return ErrCacheMemoryExceeded
 	}
 
@@ -101,7 +101,7 @@ func (c *Cache) WriteMulti(values map[string][]Value) error {
 
 	// Enough room in the cache?
 	newSize := c.size + uint64(totalSz)
-	if c.maxSize > 0 && newSize+c.flushingCachesSize > c.maxSize {
+	if c.maxSize > 0 && newSize+c.snapshotCachesSize > c.maxSize {
 		return ErrCacheMemoryExceeded
 	}
 
@@ -126,8 +126,8 @@ func (c *Cache) Snapshot() *Cache {
 	c.store = make(map[string]*entry)
 	c.size = 0
 
-	c.flushingCaches = append(c.flushingCaches, snapshot)
-	c.flushingCachesSize += snapshot.size
+	c.snapshotCaches = append(c.snapshotCaches, snapshot)
+	c.snapshotCachesSize += snapshot.size
 
 	// sort the snapshot before returning it. The compactor and any queries
 	// coming in while it writes will need the values sorted
@@ -147,22 +147,13 @@ func (c *Cache) ClearSnapshot(snapshot *Cache) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
-	caches := make([]*Cache, 0)
-	cleared := false
-	for _, cache := range c.flushingCaches {
-		if cache != snapshot {
-			caches = append(caches, cache)
-		} else {
-			cleared = true
+	for i, cache := range c.snapshotCaches {
+		if cache == snapshot {
+			c.snapshotCaches = append(c.snapshotCaches[:i], c.snapshotCaches[i+1:]...)
+			c.snapshotCachesSize -= snapshot.size
+			break
 		}
 	}
-
-	c.flushingCaches = caches
-
-	// update the size if the snapshot was cleared from the flushing caches
-	if cleared {
-		c.flushingCachesSize -= snapshot.size
-	}
 }
 
 // Size returns the number of point-calcuated bytes the cache currently uses.