I'm curious as to whether anybody has gotten PostgreSQL to work with a
database that lives on some sort of read-only medium...like a CD.

I've looked around in the newsgroups and I've seen a comment by Bruce
Momjian that it can't currently be done...and I've seen a different comment
by Tom Lane that he thought that it probably could...So...I dunno.

I've taken a database and set the read-only attributes on its files and
tried to access it via psql...and couldn't...it complained about not being
able to open pg_class.

SO...I dug around through the code a little and found where the error was
coming from and changed the code so that if the open attempt with O_RDWR
fails, the code tries again with O_RDONLY.  This was in md.c...in the mdopen
function.

This did work....I was then able to open the database and do queries and
whatnot.  Trying to insert into the table didn't give any errors...until I
tried to select the record back out, at which time it started giving me
errors such as:

ERROR:  cannot write block 7548 of pole: Permission denied

At that point, it seems that your screwed...in that even if you shut down
postgres and restart it, somewhere it knows that that database has data that
needs to be written to disk, and it refuses to continue until it does so.

OTHER than that one problem...Is anyone aware of any other problems that my
change might cause?  To be really useful, it would be necessary to go
through and make additional changes so that it can recover from a failed
write to the "read-only" database.  But it seems like it would be okay as
long as you carefully avoid changing the database.





Sun, 7 Oct 2001 23:46:14 -0400
"Kelly Harmon" <kelly.harmon@byers.com>
Accessing Database files on a "read-only" medium...like a CD.