Re: Need help with error

On Wed, Jul 05, 2000 at 04:29:16PM -0400, Tom Lane wrote:
> Steven Saner <ssaner(at)pantheranet(dot)com> writes:
> > Using Postgres 7.0 on BSDI 4.1
> > For the last several days we are getting errors that look like this:
>
> > Error: cannot write block 0 of krftmp4 [adm] blind.
>
> > An interesting thing is that in this example, krftmp4 is a table that
> > the user that got this error message would not have accessed in any
> > way.
>
> Right --- that's implicit in the blind-write logic. A blind write
> means trying to dump out a dirty page from the shared buffer pool
> that belongs to a relation your own backend hasn't touched.
>
> Since the write fails, the dirty block remains in the shared buffer
> pool, waiting for some other backend to try to dump it again and fail
> again :-(
>
> The simplest recovery method is to restart the postmaster, causing a new
> buffer pool to be set up.
>
> However, from a developer's perspective, I'm more interested in finding
> out how you got into this state in the first place. We thought we'd
> fixed all the bugs that could give rise to orphaned dirty blocks, which
> was the cause of this type of error in all the cases we'd seen so far.
> Perhaps there is still a remaining bug of that kind, or maybe you've
> found a new way to cause this problem. Do you have time to do some
> investigation before you restart the postmaster?
>
> One thing I'd like to know is why the write is failing in the first
> place. Have you deleted or renamed the krftmp4 table, or its containing
> database adm, probably not too long before these errors started
> appearing?

Well, we have had this database version/configuration in operation for
a month or so. We rebooted the server July 1 as part of our normal
maintenance procedure. It has been after that that we have begun
seeing these problems. The adm database has been around for a long
time. The krftmp4 table is not the only table that I have seen listed
in these error messages.

> > When this happens, it seems that the backend dies, which
> > ends up causing the backend connections for all users to die.
>
> That shouldn't be happening either; blind write failure is classed as
> a simple ERROR, not a FATAL error. Does any message appear in the
> postmaster log? Is a corefile dumped, and if so what do you get from
> a backtrace?

Unfortunatly, I don't believe that there is any postmaster log. I will
probably have to restart the postmaster and redirect the stdout to a
file or something. As far as I can tell there are no core files being
created.

I will probably restart the postmaster tonight and make sure that
logging is being done. Then if it happens again we might have more to
go on.

Steve