From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-4.0 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 8D6231F87F for ; Thu, 22 Nov 2018 16:43:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389322AbeKWDX3 (ORCPT ); Thu, 22 Nov 2018 22:23:29 -0500 Received: from cloud.peff.net ([104.130.231.41]:48708 "HELO cloud.peff.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1728450AbeKWDX2 (ORCPT ); Thu, 22 Nov 2018 22:23:28 -0500 Received: (qmail 24467 invoked by uid 109); 22 Nov 2018 16:43:20 -0000 Received: from Unknown (HELO peff.net) (10.0.1.2) by cloud.peff.net (qpsmtpd/0.94) with SMTP; Thu, 22 Nov 2018 16:43:20 +0000 Authentication-Results: cloud.peff.net; auth=none Received: (qmail 23516 invoked by uid 111); 22 Nov 2018 16:42:43 -0000 Received: from sigill.intra.peff.net (HELO sigill.intra.peff.net) (10.0.0.7) by peff.net (qpsmtpd/0.94) with (ECDHE-RSA-AES256-GCM-SHA384 encrypted) SMTP; Thu, 22 Nov 2018 11:42:43 -0500 Authentication-Results: peff.net; auth=none Received: by sigill.intra.peff.net (sSMTP sendmail emulation); Thu, 22 Nov 2018 11:43:18 -0500 Date: Thu, 22 Nov 2018 11:43:18 -0500 From: Jeff King To: Derrick Stolee Cc: git@vger.kernel.org, Christian Couder , Derrick Stolee Subject: Re: [PATCH 0/3] delta-island fixes Message-ID: <20181122164318.GG28192@sigill.intra.peff.net> References: <20181120094451.GA21725@sigill.intra.peff.net> <778f1fcb-8988-de42-8264-d4394ede8540@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <778f1fcb-8988-de42-8264-d4394ede8540@gmail.com> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Tue, Nov 20, 2018 at 10:06:57AM -0500, Derrick Stolee wrote: > On 11/20/2018 4:44 AM, Jeff King wrote: > > In cases like this I think it's often a good idea to have a perf test. > > Those are expensive anyway, and we'd have the double benefit of > > exercising the code and showing off the performance improvement. But the > > delta-island code only makes sense on a very specialized repo: one where > > you have multiple related but diverging histories. You could simulate > > that by picking two branches in a repository, but the effect is going to > > be miniscule. > > The changes in this series look correct. Too bad it is difficult to test. > > Perhaps we should add a performance test for the --delta-islands check that > would trigger the failure (and maybe a clone afterwards). There are lots of > freely available forks of git.git that present interesting fork structure. > Here are three that would suffice to make this interesting: > >     https://github.com/git/git >     https://github.com/git-for-windows/git >     https://github.com/microsoft/git > > Of course, running it on a specific repo is up to the person running the > perf suite. I hadn't really considered the possibility of reconstructing a fork network repository from public repos. It probably would be possible to include a script which does so, although: - I suspect it's going to be pretty expensive. We can use --reference to reduce the size of subsequent clones, but just the repacks you have to do to assemble the final shared repo can get pretty expensive. - That's 3 forks. Our real-world case has over 4000. I'm not sure of the size of the effects for smaller cases. So in short, I think it's an interesting avenue to explore, but it might turn out to be a dead-end. I'm not going to prioritize it right now, but if somebody wants to play with it, I'd be happy to look over the results. -Peff