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

Ouch! I replied to wrong mail.

At Thu, 13 Apr 2017 19:55:04 +0900 (Tokyo Standard Time), Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp> wrote in
<20170413.195504.89348773.horiguchi.kyotaro@lab.ntt.co.jp>
> 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.

The right target of "This" below is found at the following URL.

https://www.postgresql.org/message-id/CAD21AoBt_XUdppddFak661_LBM2t3CfK52aLKHG%2Bekd7SkzLmg%40mail.gmail.com

> 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