On Sat, Jan 19, 2013 at 11:27:28AM -0500, Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > Why is a clean shutdown important? If the server crashed, we would have
> > committed transactions in the WAL files which are not transfered to the
> > new server, and would be lost.
>
> > I am hesistant to even start such an old server because pg_upgrade never
> > modifies the old server. Even starting it in that case would be
> > modifying it.
>
> I'm not really following this logic. If the old cluster was in a
> crashed state, why would we not expect that starting a postmaster would
> be the best (only) way to repair the damage and make everything good
> again? Isn't that exactly what the user would have to do anyway? What
> other action would you expect him to take instead?
>
> (But, at least with the type of packaging I'm using in Fedora, he would
> first have to go through a package downgrade/reinstallation process,
> because the packaging provides no simple scripted way of manually
> starting the old postgres executable, only the new one. Moreover, what
> pg_upgrade is printing provides no help in figuring out whether that's
> the next step.)
>
> I do sympathize with taking a paranoid attitude here, but I'm failing
> to see what advantage there is in not attempting to start the old
> postmaster. In the *only* case that pg_upgrade is successfully
> protecting against with this logic, namely there's-an-active-postmaster-
> already, the postmaster is equally able to protect itself. In other
> cases it would be more helpful not less to let the postmaster analyze
> the situation.
>
> > The other problem is that if the server start fails, how do we know if
> > the failure was due to a running postmaster?
>
> Because we read the postmaster's log file, or at least tell the user to
> do so. That report would be unambiguous, unlike pg_upgrade's.
Attached is a WIP patch to give you an idea of how I am going to solve
this problem. This comment says it all:
! /*
! * If we have a postmaster.pid file, try to start the server. If
! * it starts, the pid file was stale, so stop the server. If it
! * doesn't start, assume the server is running.
! */
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +
