Re: Interval for launching the table sync worker

On Thu, Apr 13, 2017 at 11:53 AM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> On Wed, Apr 12, 2017 at 11:46 PM, Peter Eisentraut
> <peter(dot)eisentraut(at)2ndquadrant(dot)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.
>

Attached the latest patch. It didn't actually necessary to change
GetSubscriptionNotReadyRelations. I just changed the logic refreshing
the sync table state list.
Please give me feedback.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center