Thread: Re: "could not read block 0... " error followed by "database does not exist"

Hi.  What I see when I do ls on the current (corrupt)
$PGDATA/global is

...
- rw------- 1 jsjacobs deepsky     0 Feb  8 18:51 1262
...
-rw------- 1 jsjacobs deepsky   602 Feb 12 17:42 pg_auth
-rw------- 1 jsjacobs deepsky  8192 Feb 12 17:42 pg_control
-rw------- 1 jsjacobs deepsky     0 Feb 12 17:42 pg_database
-rw------- 1 jsjacobs deepsky 10927 Feb 12 21:57 pgstat.stat

I have a pgdump from a month ago.  Are you saying to restore
that to a different location and then copy over
$PGDATA/global/1262?  Do I also need to copy over
$PGDATA/global/pg_database?

Thanks,
Janet


Tom Lane wrote:
> Janet S Jacobsen <JSJacobsen@lbl.gov> writes:
>> Hi.  I am running Postgres 8.2.7 on a Linux system for over
>> a year now with no problems.
>
>> Today one of the database users reported the following error:
>
>>    psql: FATAL:  could not read block 0 of relation 1664/0/1262: read
>>    only 0 of 8192 bytes
>
> Ugh.  1262 is pg_database --- apparently something has truncated your
> pg_database table to zero bytes :-(.  Which certainly explains the
> "no such database" errors.
>
> Have you got any chance of pulling that physical file from a backup?
> The one bright spot here is that pg_database is pretty static in most
> installations, so you could probably use even a not-very-current copy.
> The file you want is $PGDATA/global/1262.
>
> I don't offhand know of any bugs in 8.2.7 that could cause this,
> though that is rather an old version ... you might want to think
> about an update to 8.2.something-recent.
>
>             regards, tom lane

Janet S Jacobsen <JSJacobsen@lbl.gov> writes:
> Hi.  What I see when I do ls on the current (corrupt)
> $PGDATA/global is

> ...
> - rw------- 1 jsjacobs deepsky     0 Feb  8 18:51 1262
> ...
> -rw------- 1 jsjacobs deepsky   602 Feb 12 17:42 pg_auth
> -rw------- 1 jsjacobs deepsky  8192 Feb 12 17:42 pg_control
> -rw------- 1 jsjacobs deepsky     0 Feb 12 17:42 pg_database
> -rw------- 1 jsjacobs deepsky 10927 Feb 12 21:57 pgstat.stat

Looks about as I'd expect from your description.  Something clobbered
1262, and then the "flat" file pg_database got updated from that.
You might want to look around at what was happening Feb 8 18:51.

> I have a pgdump from a month ago.  Are you saying to restore
> that to a different location and then copy over
> $PGDATA/global/1262?  Do I also need to copy over
> $PGDATA/global/pg_database?

Right on both.  Of course, it'd be a good idea to first make a backup of
what you have in $PGDATA now (all of it) --- you want to be able to get
back to where you are if this makes things worse.

            regards, tom lane