have_query_cache and query_cache_type

[Revathi Rangachari]

Hi

(1)  Under what circumstances the have_query_cache can become 'NO'.

(2)  Is it possible to set it as 'YES'. When I tried to do that I get error message as -
ERROR HY000: Variable 'have_query_cache' is a read only variable

(3) If have_query_cache is 'NO' and if I enable query_cache_type and set query_cache_size
TO 128MB, will the queries be read from the query cache?

Thanks
Revathi R