problem with using O_DIRECT

I tried to use O_DIRECT on Linux (SuSe) Kernel 2.6, but failed to make it run.
For example, if I added the option in the "open" of BasicOpenFile(),
I got the following error after typing "psql -l",

psql: could not connect to server: Connection refused
       Is the server running locally and accepting
       connections on Unix domain socket "/tmp/.s.PGSQL.5432"?

Any advice?

Thanks,

Brian