Re: Online enabling of checksums

> 5 апр. 2018 г., в 19:58, Magnus Hagander <magnus@hagander.net> написал(а):
> 
> 
> 
> On Thu, Apr 5, 2018 at 4:55 PM, Andrey Borodin <x4mmm@yandex-team.ru> wrote:
> 
> 
> > 5 апр. 2018 г., в 14:33, Tomas Vondra <tomas.vondra@2ndquadrant.com> написал(а):
> >
> > This patch version seems fine to me. I'm inclined to mark it RFC.
> +1
> The patch works fine for me. I've tried different combinations of backend cancelation and the only suspicious thing I found is that you can start multiple workers by cancelling launcher and not cancelling worker. Is it problematic behavior? If we run pg_enable_data_checksums() it checks for existing launcher for a reason, m.b. it should check for worker too?
> 
> I don't think it's a problem in itself -- it will cause pointless work, but not actually cause any poroblems I think (whereas duplicate launchers could cause interesting things to happen).
> 
> How did you actually cancel the launcher to end up in this situation?
select pg_enable_data_checksums(10000,1);
select pg_sleep(0.1);
select pg_cancel_backend(pid),backend_type from pg_stat_activity where backend_type ~ 'checksumhelper launcher' ;
select pg_enable_data_checksums(10000,1);
select pg_sleep(0.1);
select pg_cancel_backend(pid),backend_type from pg_stat_activity where backend_type ~ 'checksumhelper launcher' ;
select pg_enable_data_checksums(10000,1);
select pg_sleep(0.1);
select pg_cancel_backend(pid),backend_type from pg_stat_activity where backend_type ~ 'checksumhelper launcher' ;

select pid,backend_type from pg_stat_activity where backend_type ~'checks';
  pid  |     backend_type      
-------+-----------------------
 98587 | checksumhelper worker
 98589 | checksumhelper worker
 98591 | checksumhelper worker
(3 rows)

There is a way to shoot yourself in a leg then by calling pg_disable_data_checksums(), but this is extremely stupid for a user.

Best regards, Andrey Borodin.