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

On 19/04/17 14:42, Masahiko Sawada wrote:
> On Wed, Apr 19, 2017 at 5:12 PM, Kyotaro HORIGUCHI
> <horiguchi.kyotaro@lab.ntt.co.jp> wrote:
>> At Tue, 18 Apr 2017 18:40:56 +0200, Petr Jelinek <petr.jelinek@2ndquadrant.com> wrote in
<f64d87d1-bef3-5e3e-a999-ba302816a0ee@2ndquadrant.com>
>>> On 18/04/17 18:14, Peter Eisentraut wrote:
>>>> On 4/18/17 11:59, Petr Jelinek wrote:
>>>>> Hmm if we create hashtable for this, I'd say create hashtable for the
>>>>> whole table_states then. The reason why it's list now was that it seemed
>>>>> unnecessary to have hashtable when it will be empty almost always but
>>>>> there is no need to have both hashtable + list IMHO.
>>
>> I understant that but I also don't like the frequent palloc/pfree
>> in long-lasting context and double loop like Peter.
>>
>>>> The difference is that we blow away the list of states when the catalog
>>>> changes, but we keep the hash table with the start times around.  We
>>>> need two things with different life times.
>>
>> On the other hand, hash seems overdone. Addition to that, the
>> hash-version leaks stale entries while subscriptions are
>> modified. But vacuuming them costs high.
>>
>>> Why can't we just update the hashtable based on the catalog? I mean once
>>> the record is not needed in the list, the table has been synced so there
>>> is no need for the timestamp either since we'll not try to start the
>>> worker again.
> 
> I guess the table sync worker for the same table could need to be
> started again. For example, please image a case where the table
> belonging to the publication is removed from it and the corresponding
> subscription is refreshed, and then the table is added to it again. We
> have the record of the table with timestamp in the hash table when the
> table sync in the first time, but the table sync after refreshed could
> have to wait for the interval.
> 

But why do we want to wait in such case where user has explicitly
requested refresh?

--  Petr Jelinek                  http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training &
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