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