Use JSON format in the exec_filter Output plugin,output isn't instantaneous

HI 

      Use JSON format in the exec_filter Output plugin,output isn't instantaneous.
 
After viewing the FAQ document, check out the following NOTO:
`
NOTE: When using the json format, this plugin uses the Yajl library to parse the program output. Yajl buffers data internally so the output isn't always instantaneous.`

Is this a bug?
Will it be solved in the future?