hash table out of memory

Hello:
I have two tables: tenk1 and tenk2. I start postmaster with command
"postmaster -o'-fm -fn' -S" to ensure that the backend will produce
hash join planner. Then I enter psql and execute the statement:
select count(*)
from tenk1,tenk2
where tenk1.unique1=tenk2.unique2;
It reports:
ERROR: hash table out of memory. Use -B parameter to increase buffers.

Then I start postmaster with command
"postmaster -B1024 -o'-fm -fn' -S" to increase the buffer. But it still
reports the error.

The tables I used each has 16 fields and each contains 100000 tuples.

How can I overcome this problem?

Thanks in advances.
email address: sqyang(at)nudt(dot)edu(dot)cn