diff --git a/opensearch/client.go b/opensearch/client.go
index f5e3beb..4a4c041 100644
--- a/opensearch/client.go
+++ b/opensearch/client.go
@@ -154,19 +154,22 @@ func (c *Client) sendLoop(ctx context.Context) {
 			}
 
 			resp, err := c.Do(context.Background(), req, nil)
+			logger.Println("[LogStream] process BulkReq :", err)
+
 			if err != nil {
 				if netoperr, ok := err.(*net.OpError); ok && netoperr.Op == "dial" {
 					// 접속 안됨. 재시도 안함
-					logger.Println("log send bulk failed. no retry :", err)
+					logger.Println("[LogStream] send bulk failed. no retry :", err)
 					reader.printSent()
 				} else {
 					// 재시도
-					logger.Println("log send bulk failed. retry :", err)
+					logger.Println("[LogStream] send bulk failed. retry :", err)
 					failChan <- sending
 				}
 				return
 			}
 			if resp.Body == nil {
+				logger.Println("[LogStream] send bulk failed. empty response")
 				return
 			}
 			defer resp.Body.Close()
@@ -179,12 +182,15 @@ func (c *Client) sendLoop(ctx context.Context) {
 					} `json:"create"`
 				} `json:"items"`
 			}
-			json.NewDecoder(resp.Body).Decode(&respbody)
-			if !respbody.Errors {
+			if err := json.NewDecoder(resp.Body).Decode(&respbody); err != nil {
+				logger.Println("[LogStream] decode response body failed :", err)
 				return
 			}
 
-			logger.Println("log send bulk failed. retry :", respbody.Items)
+			if !respbody.Errors {
+				logger.Println("[LogStream] process BulkReq success", respbody)
+				return
+			}
 
 			var retry [][]byte
 			for i, item := range respbody.Items {
@@ -193,6 +199,8 @@ func (c *Client) sendLoop(ctx context.Context) {
 					retry = append(retry, sending[i])
 				}
 			}
+
+			logger.Println("[LogStream] send bulk failed. retry :", len(retry))
 			if len(retry) > 0 {
 				failChan <- retry
 			}
@@ -330,6 +338,7 @@ func NewClient(ctx context.Context, cfg Config) (Client, error) {
 		indexPrefix = "ds-logs-" + indexPrefix
 	}
 
+	logger.Println("[LogStream] stream indexPrefix :", indexPrefix)
 	bulkHeader := make(http.Header)
 	singleHeader := make(http.Header)
 	if len(cfg.Username) > 0 && len(cfg.Password) > 0 {