add comment for overflow

src/query/src/qExecutor.c

@@ -8914,6 +8914,7 @@ static void doSetTagValueToResultBuf(char* output, const char* val, int16_t type
 
   if (IS_VAR_DATA_TYPE(type)) {
     // Binary data overflows for sort of unknown reasons. Let trim the overflow data
+    // overflow one reason is client tag length is less than server tag length
     if (varDataTLen(val) > bytes) {
       int32_t maxLen = bytes - VARSTR_HEADER_SIZE;
       int32_t len = (varDataLen(val) > maxLen)? maxLen:varDataLen(val);