error updating a very large table

ts_defect_meta_values has 460M rows. The following query, in retrospect
not too surprisingly, runs out of memory on a 32 bit postgres:

update ts_defect_meta_values set ts_defect_date=(select ts_occur_date
from ts_defects where ts_id=ts_defect_id)

I changed the logic to update the table in 1M row batches. However,
after 159M rows, I get:

ERROR: could not extend relation 1663/16385/19505: wrote only 4096 of
8192 bytes at block 7621407

A df run on this machine shows plenty of space:

[root(at)rql32xeoall03 tmp]# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda2 276860796 152777744 110019352 59% /
/dev/sda1 101086 11283 84584 12% /boot
none 4155276 0 4155276 0% /dev/shm

The updates are done inside of a single transaction. postgres 8.3.5.

Ideas on what is going on appreciated.

Thanks,
Brian