Include snapshot size in the total cache size

This was causing a shard to appear idle when in fact a snapshot compaction
was running.  If the time was write, the compactions would be disabled and
the snapshot compaction would be aborted.

tsdb/engine/tsm1/cache.go

@@ -260,7 +260,7 @@ func (c *Cache) Write(key string, values []Value) error {
 
 	// Enough room in the cache?
 	limit := c.maxSize
-	n := c.Size() + atomic.LoadUint64(&c.snapshotSize) + addedSize
+	n := c.Size() + addedSize
 
 	if limit > 0 && n > limit {
 		atomic.AddInt64(&c.stats.WriteErr, 1)
@@ -293,7 +293,7 @@ func (c *Cache) WriteMulti(values map[string][]Value) error {
 
 	// Enough room in the cache?
 	limit := c.maxSize // maxSize is safe for reading without a lock.
-	n := c.Size() + atomic.LoadUint64(&c.snapshotSize) + addedSize
+	n := c.Size() + addedSize
 	if limit > 0 && n > limit {
 		atomic.AddInt64(&c.stats.WriteErr, 1)
 		return ErrCacheMemorySizeLimitExceeded(n, limit)
@@ -416,7 +416,7 @@ func (c *Cache) ClearSnapshot(success bool) {
 
 // Size returns the number of point-calcuated bytes the cache currently uses.
 func (c *Cache) Size() uint64 {
-	return atomic.LoadUint64(&c.size)
+	return atomic.LoadUint64(&c.size) + atomic.LoadUint64(&c.snapshotSize)
 }
 
 // increaseSize increases size by delta.

tsdb/engine/tsm1/cache_test.go

@@ -448,7 +448,7 @@ func TestCache_Snapshot_Stats(t *testing.T) {
 	}
 
 	// Store size should have been reset.
-	if got, exp := c.Size(), uint64(0); got != exp {
+	if got, exp := c.Size(), uint64(16); got != exp {
 		t.Fatalf("got %v, expected %v", got, exp)
 	}