On Wed, Feb 7, 2018 at 11:29 PM, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> Claudio Freire wrote:
>> On Wed, Feb 7, 2018 at 8:52 PM, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>> >> Waiting as you say would be akin to what the patch does by putting
>> >> vacuum on its own parallel group.
>> >
>> > I don't think it's the same. We don't need to wait until all the
>> > concurrent tests are done -- we only need to wait until the transactions
>> > that were current when the delete finished are done, which is very
>> > different since each test runs tons of small transactions rather than
>> > one single big transaction.
>>
>> Um... maybe "lock pg_class" ?
>
> I was thinking in first doing
> SELECT array_agg(DISTINCT virtualtransaction) vxids
> FROM pg_locks \gset
>
> and then in a DO block loop until
>
> SELECT DISTINCT virtualtransaction
> FROM pg_locks
> INTERSECT
> SELECT (unnest(:'vxids'::text[]));
>
> returns empty; something along those lines.
Isn't it the same though?
I can't think how a transaction wouldn't be holding at least an access
share on pg_class.