Re: [HACKERS] Interval for launching the table sync worker

I confused sync and apply workers.
sync worker failure at start causes immediate retries.

At Thu, 13 Apr 2017 11:53:27 +0900, Masahiko Sawada <sawada.mshk@gmail.com> wrote in
<CAD21AoCR6eHgk0vaHShjO4Bre_VDKjHUbL9EuWHaUgRPSPPyVQ@mail.gmail.com>
> On Wed, Apr 12, 2017 at 11:46 PM, Peter Eisentraut
> <peter.eisentraut@2ndquadrant.com> wrote:
> > On 4/12/17 00:48, Masahiko Sawada wrote:
> >> On Wed, Apr 12, 2017 at 1:28 PM, Peter Eisentraut
> >>> Perhaps instead of a global last_start_time, we store a per relation
> >>> last_start_time in SubscriptionRelState?
> >>
> >> I was thinking the same. But a problem is that the list of
> >> SubscriptionRelState is refreshed whenever the syncing table state
> >> becomes invalid (table_state_valid = false). I guess we need to
> >> improve these logic including GetSubscriptionNotReadyRelations().
> >
> > The table states are invalidated on a syscache callback from
> > pg_subscription_rel, which happens roughly speaking when a table
> > finishes the initial sync.  So if we're worried about failing tablesync
> > workers relaunching to quickly, this would only be a problem if a
> > tablesync of another table finishes right in that restart window.  That
> > doesn't seem a terrible issue to me.
> >
> 
> I think the table states are invalidated whenever the table sync
> worker starts, because the table sync worker updates its status of
> pg_subscription_rel and commits it before starting actual copy. So we
> cannot rely on that. I thought we can store last_start_time into
> pg_subscription_rel but it might be overkill. I'm now thinking to
> change GetSubscriptionNotReadyRealtions so that last_start_time in
> SubscriptionRelState is taken over to new list.

This resolves the problem but, if I understand correctly, the
many pallocs in process_syncing_tables_for_apply() is working on
ApplyContext and the context is reset before the next visit here
(in LogicalRepApplyLoop).

Although this is not a problem of this patch, this is a problem
generally.


regards,

-- 
Kyotaro Horiguchi
NTT Open Source Software Center