diff --git a/docs/developer_guides/chap07_query_coordinator.md b/docs/developer_guides/chap07_query_coordinator.md
index 8f05dcacf8..f02096caa3 100644
--- a/docs/developer_guides/chap07_query_coordinator.md
+++ b/docs/developer_guides/chap07_query_coordinator.md
@@ -247,6 +247,7 @@ type QueryNode interface {
 	// LoadSegments notifies QueryNode to load the sealed segments from storage. The load tasks are sync to this
 	// rpc, QueryNode will return after all the sealed segments are loaded.
 	LoadSegments(ctx context.Context, req *querypb.LoadSegmentsRequest) (*commonpb.Status, error)
+	// ReleaseCollection notifies Proxy to release a collection's data
 	ReleaseCollection(ctx context.Context, req *querypb.ReleaseCollectionRequest) (*commonpb.Status, error)
 	ReleasePartitions(ctx context.Context, req *querypb.ReleasePartitionsRequest) (*commonpb.Status, error)
 	ReleaseSegments(ctx context.Context, req *querypb.ReleaseSegmentsRequest) (*commonpb.Status, error)