On Mon, Nov 30, 2015 at 12:58 PM, Bruce Momjian <bruce@momjian.us> wrote: > On Mon, Nov 30, 2015 at 10:48:04PM +0530, Masahiko Sawada wrote: >> On Sun, Nov 29, 2015 at 2:21 AM, Jeff Janes <jeff.janes@gmail.com> wrote: >> > On Tue, Nov 24, 2015 at 3:13 PM, Masahiko Sawada <sawada.mshk@gmail.com> wrote: >> >> >> >> Yeah, we need to consider to compute checksum if enabled. >> >> I've changed the patch, and attached. >> >> Please review it. >> > >> > Thanks for the update. This now conflicts with the updates doesn to >> > fix pg_upgrade out-of-space issue on Windows. I've fixed (I think) the >> > conflict in order to do some testing, but I'd like to get an updated >> > patch from the author in case I did it wrong. I don't want to find >> > bugs that I just introduced myself. >> > >> >> Thank you for having a look. > > I would not bother mentioning this detail in the pg_upgrade manual page: > > + Since the format of visibility map has been changed in version 9.6, > + <application>pg_upgrade</> creates and rewrite new <literal>'_vm'</literal> > + file even if upgrading from 9.5 or before to 9.6 or later with link mode (-k).
Really? I know we don't always document things like this, but it seems like a good idea to me that we do so.
Agreed.
For me, rewriting the visibility map is a new data loss bug waiting to happen. I am worried that the group is not taking seriously the potential for catastrophe here. I think we can do it, but I think it needs these things
* Clear notice that it is happening unconditionally and unavoidably
* Log files showing it has happened, action by action
* Very clear mechanism for resolving an incomplete or interrupted upgrade process. Which VMs got upgraded? Which didn't?
* Ability to undo an upgrade attempt, somehow, ideally automatically by default
* Ability to restart a failed upgrade attempt without doing a "double upgrade", i.e. ensure transformation is immutable
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Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services