Add comment for index interface (#8712)

Signed-off-by: Ncai.zhang <cai.zhang@zilliz.com>

internal/types/types.go

@@ -86,7 +86,10 @@ type IndexNode interface {
 	Component
 	TimeTickProvider
 
+	// CreateIndex receives request from IndexCoordinator to build an index.
+	// Index building is asynchronous, so when an index building request comes, IndexNode records the task and returns.
 	CreateIndex(ctx context.Context, req *indexpb.CreateIndexRequest) (*commonpb.Status, error)
+	// GetMetrics gets the metrics about IndexNode.
 	GetMetrics(ctx context.Context, req *milvuspb.GetMetricsRequest) (*milvuspb.GetMetricsResponse, error)
 }
 
@@ -94,10 +97,20 @@ type IndexCoord interface {
 	Component
 	TimeTickProvider
 
+	// BuildIndex receives request from RootCoordinator to build an index.
+	// Index building is asynchronous, so when an index building request comes, an IndexBuildID is assigned to the task and
+	// the task is recorded in Meta. The background process assignTaskLoop will find this task and assign it to IndexNode for
+	// execution.
 	BuildIndex(ctx context.Context, req *indexpb.BuildIndexRequest) (*indexpb.BuildIndexResponse, error)
+	// DropIndex deletes indexes based on IndexID. One IndexID corresponds to the index of an entire column. A column is
+	// divided into many segments, and each segment corresponds to an IndexBuildID. IndexCoord uses IndexBuildID to record
+	// index tasks. Therefore, when DropIndex is called, delete all tasks corresponding to IndexBuildID corresponding to IndexID.
 	DropIndex(ctx context.Context, req *indexpb.DropIndexRequest) (*commonpb.Status, error)
+	// GetIndexStates gets the index states of the IndexBuildIDs in the request from RootCoordinator.
 	GetIndexStates(ctx context.Context, req *indexpb.GetIndexStatesRequest) (*indexpb.GetIndexStatesResponse, error)
+	// GetIndexFilePaths gets the index files of the IndexBuildIDs in the request from RootCoordinator.
 	GetIndexFilePaths(ctx context.Context, req *indexpb.GetIndexFilePathsRequest) (*indexpb.GetIndexFilePathsResponse, error)
+	// GetMetrics gets the metrics about IndexCoord.
 	GetMetrics(ctx context.Context, req *milvuspb.GetMetricsRequest) (*milvuspb.GetMetricsResponse, error)
 }