Re: [Bug] Logical Replication failing if the DateStyle is different in Publisher & Subscriber - Mailing list pgsql-hackers

On Thu, 21 Oct 2021 at 19:54, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> On Thu, Oct 21, 2021 at 3:04 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>>
>> On Thu, Oct 21, 2021 at 11:16 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>> >
>> > On Wed, Oct 20, 2021 at 8:12 PM Japin Li <japinli@hotmail.com> wrote:
>> > >
>> > >
>> > > On Mon, 18 Oct 2021 at 17:27, Dilip Kumar <dilipbalaut@gmail.com> wrote:
>> > > > On Mon, Oct 18, 2021 at 1:41 PM Japin Li <japinli@hotmail.com> wrote:
>> > > >
>> > > >> I attached v3 patch that set IntervalStyle to 'postgres' when the
>> > > >> server backend is walsender, and this problem has gone.
>> > > >
>> > > >> I test that set IntervalStyle to 'sql_standard' on publisher and
>> > > >> 'iso_8601' on subscriber, it works fine.
>> > > >
>> > > >> Please try v3 patch and let me know if they work as unexpected.
>> > > >> Thanks in advance.
>> > > >
>> > > > I think the idea of setting the standard DateStyle and the
>> > > > IntervalStyle on the walsender process looks fine to me.  As this will
>> > > > avoid extra network round trips as Tom mentioned.
>> > >
>> > > After some test, I find we also should set the extra_float_digits to avoid
>> > > precision lossing.
>> >
>> > I'm concerned that it sets parameters too early since wal senders end
>> > up setting the parameters regardless of logical decoding plugins. It
>> > might be better to force the parameters within the plugin for logical
>> > replication, pgoutput, in order to avoid affecting other plugins? On
>> > the other hand, if we do so, we will need to handle table sync worker
>> > cases separately since they copy data via COPY executed by the wal
>> > sender process. For example, we can have table sync workers set the
>> > parameters.
>>
>> You mean table sync worker to set over the replication connection
>> right?  I think that was the first solution where normal workers, as
>> well as table sync workers, were setting over the replication
>> connection, but Tom suggested that setting on the walsender is a
>> better option as we can avoid the network round trip.
>
> Right.
>
> BTW I think we can set the parameters from the subscriber side without
> additional network round trips by specifying the "options" parameter
> in the connection string, no?
>

Yes, we can.  However, each client should be concerned the style for
datestyle, IMO it is boring.

>> If we want to set it over the replication connection then do it for
>> both as Japin's first patch is doing, otherwise, I am not seeing any
>> big issue in setting it early in the walsender also.  I think it is
>> good to let walsender always send in the standard format which can be
>> understood by other node, no?
>
> Yeah, probably the change on HEAD is fine but I'm a bit concerned
> about possible issues on back branches like if the user expects to get
> date data in the style of DateStyle setting on the server via
> pg_recvlogical, this change could break it.
>

How it breaks?  The user also can specify the "options" to get date data
in the style which they are wanted. Right?

-- 
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.