Re: do only critical work during single-user vacuum?

On Thu, Feb 3, 2022 at 5:08 PM John Naylor <john.naylor@enterprisedb.com> wrote:
> Looking closer, there is a function defined by an extension. I'd have
> to dig further to see if writes happen. The error is exactly what
> we've been talking about:
>
> 2022-01-03 22:03:23 PST ERROR: database is not accepting commands to
> avoid wraparound data loss in database "<redacted>"
> 2022-01-03 22:03:23 PST HINT: Stop the postmaster and vacuum that
> database in single-user mode. You might also need to commit or roll
> back old prepared transactions.

That error comes from GetNewTransactionId(), so that function must
either try to execute DML or do something else which causes an XID to
be assigned. I think a plain SELECT should work just fine.

-- 
Robert Haas
EDB: http://www.enterprisedb.com