Re: recovering from "found xmin ... from before relfrozenxid ..."

On Wed, Sep 16, 2020 at 1:25 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> > On Mon, Sep 14, 2020 at 6:26 AM Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com> wrote:
> >> Thanks for reporting. I'm able to reproduce the issue by creating some
> >> delay just before "-- now create an unused line pointer" and use the
> >> delay to start a new session either with repeatable read or
> >> serializable transaction isolation level and run some query on the
> >> test table. To fix this, as you suggested I've converted the test
> >> table to the temp table. Attached is the patch with the changes.
> >> Please have a look and let me know about any concerns.
>
> > Tom, do you have any concerns about this fix?
>
> It seems OK as far as it goes. Two thoughts:
>
> * Do we need a comment in the test pointing out that the table must be
> temp to ensure that we get stable vacuum results? Or will the commit
> log message be enough documentation?
>

I'll add a note for this.

> * Should any of the other tables in the test be converted to temp?
> I see that the other test cases are kluging around related issues
> by dint of never committing their tables at all. It's not clear
> to me how badly those test cases have been distorted by that, or
> whether it means they're testing less-than-typical situations.
>

Are you trying to say that we can achieve the things being done in
test-case 1 and 2 by having a single temp table and we should aim for
it because it will make the test-case more efficient and easy to
maintain? If so, I will try to do the necessary changes and submit a
new patch for it. please confirm.

Thanks,

--
With Regards,
Ashutosh Sharma
EnterpriseDB:http://www.enterprisedb.com