Re: Re: protocol version negotiation (Re: Libpq PGRES_COPY_BOTH - version compatibility)

Hi Tom and Robert,

I added a mechanism to fall back to v3.0 if the BE fails to start when FE initiates a connection with v3.1 (with optional startup parameters). This completely eliminates the need to backpatch older servers, ie newer FE can connect to older BE. Please let me know what you think.

Thanks,
Badrul

-----Original Message-----
From: Robert Haas [mailto:robertmhaas(at)gmail(dot)com]
Sent: Wednesday, October 4, 2017 4:54 AM
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Badrul Chowdhury <bachow(at)microsoft(dot)com>; Satyanarayana Narlapuram <Satyanarayana(dot)Narlapuram(at)microsoft(dot)com>; Craig Ringer <craig(at)2ndquadrant(dot)com>; Peter Eisentraut <peter_e(at)gmx(dot)net>; Magnus Hagander <magnus(at)hagander(dot)net>; PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] Re: protocol version negotiation (Re: Libpq PGRES_COPY_BOTH - version compatibility)

On Tue, Oct 3, 2017 at 9:46 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Badrul Chowdhury <bachow(at)microsoft(dot)com> writes:
>> 1. Pgwire protocol v3.0 with negotiation is called v3.1.
>> 2. There are 2 patches for the change: a BE-specific patch that will be backported and a FE-specific patch that is only for pg10 and above.
>
> TBH, anything that presupposes a backported change in the backend is
> broken by definition. We expect libpq to be able to connect to older
> servers, and that has to include servers that didn't get this memo.
>
> It would be all right for libpq to make a second connection attempt if
> its first one fails, as we did in the 2.0 -> 3.0 change.

Hmm, that's another approach, but I prefer the one advocated by Tom Lane.

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Robert Haas
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