Re: [PATCH/RFC] config: default to protocol v2

From: Jeff King <peff@peff.net>
Date: Jul 9, 2020, 23:00 UTC
Message-ID: <20200709230038.GB664420@coredump.intra.peff.net>
In-Reply-To: <xmqq7dve2etl.fsf@gitster.c.googlers.com>

On Wed, Jul 08, 2020 at 08:42:46AM -0700, Junio C Hamano wrote:

Show 10 quoted lines

> I am afraid that "there probably aren't other" may be overly
> optimistic, as the bug in 2.26 crippled the negotiation logic and
> forced it to punt, which was so severe that it would have hidden any
> other bugs in the negotiation logic.  If there is another bug in v2
> negotiation logic that makes the sender to omit objects that should
> be sent, it would not have been observed in 2.26 because the effect
> of the more severe bug was to cripple the negotiation logic itself
> and to make it punt, sending more objects all the way down the
> history.  Now, with that larger bug fixed post 2.26, we can start to
> see if there are other bugs hidden by it.

I half-agree with this. The negotiation logic wasn't completely broken, and usually did the right thing. It was only the max_in_vain counting that was wrong. So definitely there could be another bug lurking that was hidden by that failure, and/or our fix could be incomplete. But I think we can have some confidence that there aren't other show-stopping bugs (in the negotiation code or elsewhere in v2) that showed up in other situations (and the real-world success reports we already got for that particular bug are also encouraging).

So I'm not especially worried about having a repeat of the v2.26 situation (but I agree it's not impossible).

Show 6 quoted lines

> In any case, we've learned in 2.26 that it is unlikely that such
> bugs would be uncovered until v2 is made the default again in a
> released version to be used by more users.
> 
> So, let's flip the default in -rc0; we can revert if we see
> something funny in 2.28.1 in the worst case.

And obviously I'm fine with this, given that my assessment of the risk is even less than yours. :)

-Peff