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-Status: No, score=-3.8 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by dcvr.yhbt.net (Postfix) with ESMTP id 54D1D1F4B4 for ; Tue, 15 Sep 2020 19:32:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727954AbgIOTcp (ORCPT ); Tue, 15 Sep 2020 15:32:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53388 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727963AbgIOTci (ORCPT ); Tue, 15 Sep 2020 15:32:38 -0400 Received: from mail-qv1-xf41.google.com (mail-qv1-xf41.google.com [IPv6:2607:f8b0:4864:20::f41]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F3165C06178C for ; Tue, 15 Sep 2020 12:32:04 -0700 (PDT) Received: by mail-qv1-xf41.google.com with SMTP id db4so2321170qvb.4 for ; Tue, 15 Sep 2020 12:32:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ttaylorr-com.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to; bh=wDHULpkCcDEGpO7QSZmKCcPeBagkYbOmwb9Ob262loo=; b=VOfgUfLA784aIEgmhZyfc2cB/9egnsaT8cbFHtdZyx8h3NNwdlXoGHhAyxTAcdvVrL rWw1XVQa1ySvvjqpJRwFiHE+MKqvYEV1H12NpXOhe5fvU+WK/lrRHcm9DRshaohtneUJ wY1+hxI6P8Ay+injuHUOx+xAdCpsN6N5IoOREVV8H680zS0v58WIwwSkonxMMuhf283w ZcmqeC7e0HeoZI4+fQX7XrmTSDq856MCka5btYSSFkVYkHC8BPjEx5lCvhaaiITWiHU3 ZI2y5qNY10hHLlgElliZr6QMw7lkBxSmo7Ds6qdtB2dcBbZi1AdI/42gYyMOst8+yu4c NrOQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=wDHULpkCcDEGpO7QSZmKCcPeBagkYbOmwb9Ob262loo=; b=J3Nl0KvKUz0HMPYbiUJnkJVeeOdTk9chBQtWUqX/CrjgSYg0/kiM9iSu/1YS01W5go IdK0JpsqTFCQQZd57rCG1nDMZVh7x7cdyFHf1a/QOtTcLnH6mh9cfigOAvewsMV6P13B 0XIUk1bCj6bDgmznK0OAGDLV7hNrlLmGL5Fn1sgRbiyXUxVKDmJT1u3tRcXWf05273Wn 2qKehwZCtYIb+NWdZETT6E2b/8Kweqnj/XlJh3VMqqrgvZMTINViRynixCz1J+VuIJt9 TL+UpfOlTm2X3Eg6ZErwNGCaJLEXfMiZcoPGsk7bsLrOhjnaXVBO7bovOUPcM1zLZA8V 740g== X-Gm-Message-State: AOAM533D/zdx70TKvO3nMQ2XnlNW3yJN7j/YYbC1qf2XWq3TlrVovnp8 Vj7It4ZrdvKYCpu6H3gRayLE3w== X-Google-Smtp-Source: ABdhPJxTxDzZEwVwPzylTxrfnsfMcFMI2uZ20+LYiw4mf+6yd1+o6XZwyfgHUsG59E2/LQcH4UNFxg== X-Received: by 2002:a0c:9a01:: with SMTP id p1mr3209926qvd.61.1600198324206; Tue, 15 Sep 2020 12:32:04 -0700 (PDT) Received: from localhost ([2605:9480:22e:ff10:209c:e081:d56c:21a0]) by smtp.gmail.com with ESMTPSA id w44sm18315766qth.9.2020.09.15.12.32.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Sep 2020 12:32:03 -0700 (PDT) Date: Tue, 15 Sep 2020 15:32:01 -0400 From: Taylor Blau To: Jakub =?utf-8?B?TmFyxJlic2tp?= Cc: Junio C Hamano , git@vger.kernel.org, Abhishek Kumar , Derrick Stolee , Taylor Blau Subject: Re: What's cooking in git.git (Sep 2020, #03; Wed, 9) Message-ID: <20200915193201.GA1741@nand.local> References: <85ft7ivp1t.fsf@LAPTOP-ACER-ASPIRE-F5.i-did-not-set--mail-host-address--so-tickle-me> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <85ft7ivp1t.fsf@LAPTOP-ACER-ASPIRE-F5.i-did-not-set--mail-host-address--so-tickle-me> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Hi Jakub, On Tue, Sep 15, 2020 at 09:05:18PM +0200, Jakub Narębski wrote: > I'd like to point out that latest series of patches by Abhishek Kumar > which are final part of 'Implement Generation Number v2' is at what I > believe is next to final iteration: > > "[PATCH v3 00/11] [GSoC] Implement Corrected Commit Date" > https://lore.kernel.org/git/pull.676.v3.git.1597509583.gitgitgadget@gmail.com/T/#u > > It is waiting for the decision on *how to implement storing* new > generation number in the commit-graph file: should we store corrected > commit date directly as 64 bit value, or should we store corrected > commit date offset as 32 bit value with overflow handling? > > Switching from 64 bits to 32 bits halves the size of the GDAT > (Generation DATa) chunk, but decreases the size of the commit-graph file > by at most 7%. For large repository, like MS Windows with 3M commits in > 2019 it would mean decreasing the size of the commit-graph file by > 11.8 MiB (if I calculated it correctly). > > Because corrected commit date offsets are not monotone, that is after > value that doesn't fit in 32 bits (in parent) there can be one that does > (in child). It is extremely unlikely that in real repositories there > would be that large corrections needed, but it can happen in theory, and > therfore we need some way to handle overflow if we choose this option. > And of course we should test that overflow handling works correctly. > > So there is tradeoff between complexity and commit-graph file size. If you think that not being able to fit into 32 bits is unlikely, then I don't think it makes sense to store those same values inside of 64 bits, either. Of course, that means implementing overflow detection, but that's a small price to pay for shaving off extra data from the commit-graph file. > Best, > -- > Jakub Narębski Thanks, Taylor