On 3 May 2016 at 18:07, Tom Lane <t...@sss.pgh.pa.us> wrote:

> Or at least, it did until Simon decided that ALTER TABLE RESET
> doesn't require AccessExclusiveLock.

On reflection, this still seems like a good idea.

> Now you get a failure.

Failure condition as an exception to that.

> I haven't tried to construct a pre-9.1 database that would trigger
> this, but you can make it happen by applying the attached patch
> to create a toast-table-less table in the regression tests,
> and then doing "make check" in src/bin/pg_upgrade.  You get this:
> ...
> Restoring database schemas in the new cluster
>                                                             ok
> Creating newly-required TOAST tables                        SQL command
> failed
> ALTER TABLE "public"."i_once_had_a_toast_table" RESET
> (binary_upgrade_dummy_option);
> ERROR:  AccessExclusiveLock required to add toast table.
> Failure, exiting

It appears that pg_upgrade is depending upon an undocumented side-effect of

I would say this side-effect should not exist, which IIUC is the same
conclusion on your latest post.

If pg_upgrade needs this, we should implement a specific function that does
what pg_upgrade needs. That way we can isolate the requirement for an
AccessExclusiveLock to the place that needs it: pg_upgrade. That will also
make it less fragile in the future. I don't think that needs a specific
command, just a function.

I accept that it is my bug and should fix it.

Simon Riggs                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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