Re: COPY, lock release and MVCC

On Tue, 2020-05-12 at 11:50 -0400, Tom Lane wrote:
> Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> writes:
> > On Mon, 2020-05-11 at 15:43 -0400, Robert Haas wrote:
> > > On Fri, May 8, 2020 at 4:58 AM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> wrote:
> > > > I happened to notice that COPY TO releases the ACCESS SHARE lock
> > > > on the table right when the command ends rather than holding it
> > > > until the end of the transaction:
> > > That seems inconsistent with what an INSERT statement would do, and thus bad.
> > Well, should we fix the code or the documentation?
>
> I'd agree with fixing the code. Early lock release is something we do on
> system catalog accesses, and while it hasn't bitten us yet, I've been
> kind of expecting that someday it will. We should not do it on SQL-driven
> accesses to user tables.
>
> Having said that, I'd vote for just changing it in HEAD, not
> back-patching. It's not clear that there are consequences bad enough
> to merit a back-patched behavior change.

Agreed.

Here is a patch.

Yours,
Laurenz Albe