Re: libpq changes for synchronous replication

The one time this year top-posting seems appropriate...this patch seems 
stalled waiting for some sort of response to the concerns Alvaro raised 
here.

Alvaro Herrera wrote:
> Excerpts from Fujii Masao's message of jue nov 25 10:47:12 -0300 2010:
>
>   
>> The attached patch s/CopyXLog/CopyBoth/g and adds the description
>> about CopyBoth into the COPY section.
>>     
>
> I gave this a look.  It seems good, but I'm not sure about this bit:
>
> +               case 'W':       /* Start Copy Both */
> +                   /*
> +                    * We don't need to use getCopyStart here since CopyBothResponse
> +                    * specifies neither the copy format nor the number of columns in
> +                    * the Copy data. They should be always zero.
> +                    */
> +                   conn->result = PQmakeEmptyPGresult(conn, PGRES_COPY_OUT);
> +                   if (!conn->result)
> +                       return;
> +                   conn->asyncStatus = PGASYNC_COPY_BOTH;
> +                   conn->copy_already_done = 0;
> +                   break;
>
> I guess this was OK when this was conceived as CopyXlog, but since it's
> now a generic mechanism, this seems a bit unwise.  Should this be
> reconsidered so that it's possible to change the format or number of
> columns?
>
> (The paragraph added to the docs is also a bit too specific about this
> being used exclusively in streaming replication, ISTM)
>
>   
>> While modifying the code, it occurred to me that we might have to add new
>> ExecStatusType like PGRES_COPY_BOTH and use that for CopyBoth mode,
>> for the sake of consistency. But since it's just alias of PGRES_COPY_BOTH
>> for now, i.e., there is no specific behavior for that ExecStatusType, I don't
>> think that it's worth adding that yet.
>>     
>
> I'm not so sure about this.  If we think that it's worth adding a new
> possible state, we should do so now; we will not be able to change this
> behavior later.
>