Re: Accessing Database files on a "read-only" medium...like

I wonder if you shut down the postmaster and restart if that would make
it work again.  I can't imagine where it would store table size
information if the area is read-only.  Adding data, full vacuum, restart
postmaster should allow read-only databases.

---------------------------------------------------------------------------

> 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.
> 
> 
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 6: Have you searched our list archives?
> 
> http://archives.postgresql.org
> 

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
853-3000+  If your life is a hard drive,     |  830 Blythe Avenue +  Christ can be your backup.        |  Drexel Hill,
Pennsylvania19026