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=-3.9 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_BLOCKED,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 B73861F4B4 for ; Fri, 29 Jan 2021 23:15:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229866AbhA2XLk (ORCPT ); Fri, 29 Jan 2021 18:11:40 -0500 Received: from pb-smtp20.pobox.com ([173.228.157.52]:52055 "EHLO pb-smtp20.pobox.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229683AbhA2XLj (ORCPT ); Fri, 29 Jan 2021 18:11:39 -0500 Received: from pb-smtp20.pobox.com (unknown [127.0.0.1]) by pb-smtp20.pobox.com (Postfix) with ESMTP id 1E75C108DFE; Fri, 29 Jan 2021 18:10:56 -0500 (EST) (envelope-from junio@pobox.com) DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=pobox.com; h=from:to:cc :subject:references:date:in-reply-to:message-id:mime-version :content-type:content-transfer-encoding; s=sasl; bh=wsUbltmqwUxL gqAhqdKID4Fun54=; b=j92QYc493YguUhVSGX01BN1A6H4YA4nNRqHDHvVJXhZO H09l674Jr9DtjDEjyo8JrzxuSV1ltV4gLvl8znEhZFYKX+Qre/YkkCb3+NDiyn5y kmfNkRAZ2Iro37kK3xBjXtX/pRUwSCuvxGJuABYx8mTOz7915haBfUZ+EIkIsnk= DomainKey-Signature: a=rsa-sha1; c=nofws; d=pobox.com; h=from:to:cc :subject:references:date:in-reply-to:message-id:mime-version :content-type:content-transfer-encoding; q=dns; s=sasl; b=vrZsg9 Z9a4KXSJ1L3EA9ItNPGTWbD0t8EuPYVQkwOcaovDkEY2RlA3L3SXFZytrDZKEFnL CV5vpQobX5NG9LeeoelM/BI75ogKcSSrZUntqaiWS7ri9adWTupwHRaupEzKJ+nK NKcZXI2fgdZuIiqcHn4/80gAz3nFj9+VYmyPc= Received: from pb-smtp20.sea.icgroup.com (unknown [127.0.0.1]) by pb-smtp20.pobox.com (Postfix) with ESMTP id 17399108DFD; Fri, 29 Jan 2021 18:10:56 -0500 (EST) (envelope-from junio@pobox.com) Received: from pobox.com (unknown [34.74.119.39]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by pb-smtp20.pobox.com (Postfix) with ESMTPSA id 58142108DFB; Fri, 29 Jan 2021 18:10:53 -0500 (EST) (envelope-from junio@pobox.com) From: Junio C Hamano To: Taylor Blau Cc: Jeff King , git@vger.kernel.org, dstolee@microsoft.com Subject: Re: [PATCH 03/10] builtin/pack-objects.c: learn '--assume-kept-packs-closed' References: <2da42e9ca26c9ef914b8b044047d505f00a27e20.1611098616.git.me@ttaylorr.com> Date: Fri, 29 Jan 2021 15:10:51 -0800 In-Reply-To: (Taylor Blau's message of "Fri, 29 Jan 2021 17:53:58 -0500") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1.90 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 X-Pobox-Relay-ID: 3C1FC56C-6287-11EB-9430-E43E2BB96649-77302942!pb-smtp20.pobox.com Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Taylor Blau writes: > On Fri, Jan 29, 2021 at 05:43:32PM -0500, Jeff King wrote: >> So I think the paths forward are either: >> >> - come up with an air-tight system of making sure that we know packs >> we claim are closed under reachability really are (perhaps some >> marker that says "I was generated by repack -a") >> >> - have a "roll-up" mode that does not care about reachability at all= , >> and just takes any objects from a particular set of packs (plus >> probably loose objects) >> >> I'm still thinking aloud here, and not really sure which is a better >> path. I do feel like the failure modes for the second one are less >> risky. > > The more I think about it, the more I feel that the second option is th= e > right approach. It seems like if you were na=C3=AFvely implementing thi= s from > scratch, that you'd pick the second one (i.e., have pack-objects > understand a new input mode, and then make a pack based on that). Yes, "roll-up" mode would be a sensible thing to have, as long as we can keep pruning out of the picture for now. But in the end, I do think "stop at any object in this frozen pack---these objects go all the way down to root and we know they are reachable" optimization that would give 'prune' a performance boost with small margin of false positive about reachability (i.e. we may never be able to prune away an object in such a pack, even when it becomes unreachable) would be a valuable thing to have in a practical system, so from that point of view, the work done in these patches are not lost ;-) The efficiency issue of the resulting pack I mentioned earlier in a separate message is there in the "roll-up" mode, though.