pgsql-bugs@postgresql.org writes:
> FATAL 2: open of /usr/share/postgresql/data/pg_clog/0C81 failed: No such file or directory
This indicates corrupted data --- specifically, a trashed transaction ID
in a row header. In all the cases I've been able to examine, this was
just the first symptom of more widespread corruption (usually, a whole
disk page is trashed). I recommend checking for hardware problems;
you may have bad RAM or a flaky disk drive or cable.
regards, tom lane