Kelly Harmon <kelly.harmon@byers.com> wrote in message news:9pr7f7$k0j$1@news.tht.net...
> 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.

Isn't it the WAL who 'remembers' this info?

--
Serguei A. Mokhov
  


Mon, 8 Oct 2001 00:23:18 -0400
"Serguei Mokhov" <sa_mokho@alcor.concordia.ca>
Re: Accessing Database files on a "read-only" medium...like a CD.
"Serguei Mokhov" <sa_mokho@alcor.concordia.ca> writes:
> Kelly Harmon <kelly.harmon@byers.com> wrote in message news:9pr7f7$k0j$1@news.tht.net...
>> 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.

> Isn't it the WAL who 'remembers' this info?

Both WAL and pg_log *must* be on writable media, so there's really no
chance of putting the whole of a $PGDATA tree onto a CD.  However one
could imagine putting individual databases (or even individual tables)
onto CD.  One thing you'd have to watch out for is that Postgres
may try to update on-row commit status bits even during a read-only
operation such as SELECT.  The best way to deal with that would be to
VACUUM the table or database before moving it to read-only storage.
VACUUM would leave the status bits all set correctly.

We've talked repeatedly about implementing a notion of tablespaces
to allow DBAs to exercise more control over where tables are kept.
Maybe it'd make sense to allow tablespaces to be marked read-only, too.

			regards, tom lane

Mon, 08 Oct 2001 12:12:06 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: Accessing Database files on a "read-only" medium...like a CD. 