BLOCKCACHE not work in console

I'm testing the speed. At the time of the request, I know part of the key.
```
scan 'id_bank',

{STARTROW=>"24168557"+"\137",STOPROW=>"24168557"+"\177",COLUMNS => ['high', 'low'], BLOCKCACHE => 'true'}

```
When I run the scan, the response returns a short time, and if I make a second request, the answer is already returned quickly, why?