pg_dump, custom format and changes in the dump file

Hello,

We have a system where we take periodic dumps from PgSQL 8.0.1
database and put those dumps under version control (Subversion).

Now the problem is that when we take a custom format dump with:

pg_dump --format=c --compress=0 --column-inserts \
--use-set-session-authorization \
db_name > db_dump_file

The dump file has been changed when at the same time taken ASCII dump
(--format=p) is identical to the previous one.

So, Is there any way to stabilize pg_dump with custom format so that
the dump file won't change without real db changes?

Thank you for your help,
Jani

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Jani Averbach