size difference between du and PG_CLASS

Hi All,

We have a big difference between du and PG_CLASS:

du -hs ./base/17613

21G ./base/17613

select sum(relpages)*8/1024/1024 from pg_class;

?column?

----------

11

(1 row)

I am sure I run the select under the right database (17613).

I know there are some files under:

du -hs base/17613/pgsql_tmp

1.7G base/17613/pgsql_tmp

But the difference is still around 8G (21G - 11G - 1.7G).

When I check timestamp on files under directory 17613, I found there are
many old relfilenode which do not exist

in the pg_class any more. We had bounced the PG server, those files are
still there.

Does PG remove those files which are not longer used by PG after server
bounce?

Which files can I safely delete?

Thanks,

PS: PG version 7.3.2 and OS version Red Hat Linux release 7.3 (Valhalla)