printing results of query to file in different times

I'm trying to understand what postgresql doing in an issue that I'm having.
Our app team wrote a function that runs with a cursor over the results of a
query and via the utl_file func they write some columns to a file. I dont
understand why, but postgresql write the data into the file in the fs in
parts. I mean that it runs the query and it takes time to get back results
and when I see that the results back postgresql write to file the data and
then suddenly stops for X minutes. After those x minutes it starts again to
write the data and it continues that way until its done. The query returns
total *100* rows. I want to understand why it stops suddenly. There arent
any locks in the database during this operation.

my function looks like that :

func(a,b,c...)

cursor cr for

select ab,c,d,e.....

begin

raise notice - 'starting loop time - %',timeofday();

for cr_record in cr

Raise notice 'print to file - '%',timeofday();

utl_file.write(file,cr_record)

end loop

end

I see the log of the running the next output :

starting loop 16:00

print to file : 16:03

print to file : 16:03

print to file : 16:07

print to file : 16:07

print to file : 16:07

print to file : 16:010

......

Can somebody explain to me this kind of behavior ? Why is it taking some
much time to write and in different minutes after the query already been
executed and finished ? Mybe I'm getting from the cursor only part of the
rows ?