Re: [HACKERS] logical decoding of two-phase transactions

On Tue, Mar 9, 2021 at 3:02 PM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
>
> On Mon, Mar 8, 2021 at 4:58 PM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> >
> > + while (AnyTablesyncInProgress())
> > + {
> > + process_syncing_tables(begin_data.final_lsn);
> > +
> > + /* This latch is to prevent 100% CPU looping. */
> > + (void) WaitLatch(MyLatch,
> > + WL_LATCH_SET
> > | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
> > + 1000L,
> > WAIT_EVENT_LOGICAL_SYNC_STATE_CHANGE);
> > + ResetLatch(MyLatch);
> > + }
> > Should we have CHECK_FOR_INTERRUPTS inside the while loop?
>
> The process_syncing_tables will end up in the
> process_syncing_tables_for_apply() function. And in that function IIUC
> the apply worker is spending most of the time waiting for the
> tablesync to achieve SYNCDONE state.
> See wait_for_relation_state_change(rstate->relid, SUBREL_STATE_SYNCDONE);
>

But, I think for large copy, it won't wait in that state because the
tablesync worker will still be in SUBREL_STATE_DATASYNC state and we
wait for SUBREL_STATE_SYNCDONE state only after the initial copy is
finished. So, I think it is a good idea to call CHECK_FOR_INTERRUPTS
in this loop.

--
With Regards,
Amit Kapila.