Counting the occurences of a substring within a very large text

Hello,

I'd like to count the number linebreaks within a string,
but I get a memory allocation error when using regexp_matches or regexp_split_to_table.

Any idea for an alternative to this problem ?

select count(*)-1 from
( select regexp_split_to_table(full_message,'(\n)', 'g')
from mytable
where id =-2146999703
)foo;

ERROR: invalid memory alloc request size 1447215584

regards,

Marc Mamin