Re: Perform streaming logical transactions by background workers and parallel apply

On Tue, Feb 14, 2023 at 3:58 PM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
>
> On Tue, Feb 14, 2023 at 5:04 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Fri, Feb 10, 2023 at 8:56 AM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
> > >
> > > On Fri, Feb 10, 2023 at 1:32 PM houzj(dot)fnst(at)fujitsu(dot)com
> > > <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> > > >
> > > > On Tuesday, February 7, 2023 11:17 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > > > >
> > > > > On Mon, Feb 6, 2023 at 3:43 PM houzj(dot)fnst(at)fujitsu(dot)com
> > > > > <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> > > > > >
> > > > > > while reading the code, I noticed that in pa_send_data() we set wait
> > > > > > event to WAIT_EVENT_LOGICAL_PARALLEL_APPLY_STATE_CHANGE while
> > > > > sending
> > > > > > the message to the queue. Because this state is used in multiple
> > > > > > places, user might not be able to distinguish what they are waiting
> > > > > > for. So It seems we'd better to use WAIT_EVENT_MQ_SEND here which will
> > > > > > be eaier to distinguish and understand. Here is a tiny patch for that.
> > > > > >
> > > >
> > > > As discussed[1], we'd better invent a new state for this purpose, so here is the patch
> > > > that does the same.
> > > >
> > > > [1] https://www.postgresql.org/message-id/CAA4eK1LTud4FLRbS0QqdZ-pjSxwfFLHC1Dx%3D6Q7nyROCvvPSfw%40mail.gmail.com
> > > >
> > >
> > > My first impression was the
> > > WAIT_EVENT_LOGICAL_PARALLEL_APPLY_SEND_DATA name seemed misleading
> > > because that makes it sound like the parallel apply worker is doing
> > > the sending, but IIUC it's really the opposite.
> > >
> >
> > So, how about WAIT_EVENT_LOGICAL_APPLY_SEND_DATA?
> >
>
> Yes, IIUC all the LR events are named WAIT_EVENT_LOGICAL_xxx.
>
> So names like the below seem correct format:
>
> a) WAIT_EVENT_LOGICAL_APPLY_SEND_DATA
> b) WAIT_EVENT_LOGICAL_LEADER_SEND_DATA
> c) WAIT_EVENT_LOGICAL_LEADER_APPLY_SEND_DATA

Personally I'm fine even without "LEADER" in the wait event name since
we don't have "who is waiting" in it. IIUC a row of pg_stat_activity
shows who, and the wait event name shows "what the process is
waiting". So I prefer (a).

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com