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: AS53758 23.128.96.0/24 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 0F2A61F8C1 for ; Fri, 1 May 2020 22:55:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726554AbgEAWzC (ORCPT ); Fri, 1 May 2020 18:55:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54894 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1726045AbgEAWzC (ORCPT ); Fri, 1 May 2020 18:55:02 -0400 Received: from mail-pf1-x444.google.com (mail-pf1-x444.google.com [IPv6:2607:f8b0:4864:20::444]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6242CC061A0C for ; Fri, 1 May 2020 15:55:02 -0700 (PDT) Received: by mail-pf1-x444.google.com with SMTP id 145so2177968pfw.13 for ; Fri, 01 May 2020 15:55:02 -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:in-reply-to; bh=mOB3/PxBNnmfPCHpn1WAWEulRYW0+5D5H4Dij5PCFU8=; b=AI5/kqszXspFvcRZCTHEiM5ZD6nBcZJQMH9mqJ58u4bvspMpGTucRqAXvjhD/XrQnN +vHhLqd9RQmNl5r6SbnLDfrjo4d+4EuRlVLPDK2UIMSh4hO6qsX3l60qC9iuoWJGzZ+R wbBgXN3cNUo+LbUYgPSzniW3pSO2VwdchAGJdXRCxTLARqOGa1JR956A0Cs8TmYzV4Nk 4mCoYUmi6HoT9MT2Dl41ckio+rO8PeOzd3oRnhnYpkFwbMJZuS+RExHWm4A4ZmHO3aR0 /TkorHJY7flcKJQRkliMMKnTnZuiIZ35jATyN834Xxo94eOGIIcwhkwnw0347TKVrmwf AHRw== 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:in-reply-to; bh=mOB3/PxBNnmfPCHpn1WAWEulRYW0+5D5H4Dij5PCFU8=; b=kCxjGOzDlLWMjKU94c3RaTMArcdjedKqguGp4bHW4LV0+xipP+5Eiuz99EwGBYiA7S 7GQx6YAvDafzDMEm6o5f7SgjK/3SD9BLZC2NpJlpADAW9rtoBlvTULkXjUeyGb6dH409 LHO8e0wX/bfztfZ9ho5W7r6dP3aXNpKNDDUtjvythXu/0F8dSEVanNP3RILp/gkgB5Mi 1Ly7aVWZTXHry7cOUWK5FyV5RQUV2GtUtRr4abK92ulw/rXPE82LRIqdD2uWqd2FNFQm se72C43YHNylph+kPiZ5eItQ1bnCoDtcZrU+k5Gldf9IlIQtOLcH3tZvkbvhnhlWSLa1 /qMA== X-Gm-Message-State: AGi0PuZ54xFDacb3Z0T4GOFwRGr9DFKODGW4C9epY0Bk4WAejUUcNXfP GUPquWyAeWvLNoAWFVqQaPU9Sw== X-Google-Smtp-Source: APiQypLDJraVPVUDgwawUfrkggiFlvfO2On/YawH/fVDgJkx9o/hoM3s+x4CdhWQmXJXxUw/xPVuRQ== X-Received: by 2002:a63:5c24:: with SMTP id q36mr6013356pgb.377.1588373701658; Fri, 01 May 2020 15:55:01 -0700 (PDT) Received: from localhost ([8.44.146.30]) by smtp.gmail.com with ESMTPSA id y21sm3005134pfm.219.2020.05.01.15.55.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 01 May 2020 15:55:01 -0700 (PDT) Date: Fri, 1 May 2020 16:55:00 -0600 From: Taylor Blau To: Derrick Stolee via GitGitGadget Cc: git@vger.kernel.org, peff@peff.net, me@ttaylorr.com, garimasigit@gmail.com, szeder.dev@gmail.com, jnareb@gmail.com, Derrick Stolee Subject: Re: [PATCH 03/12] Documentation: changed-path Bloom filters use byte words Message-ID: <20200501225500.GA46146@syl.local> References: <03b2c84db36754b321dd15cd8a9e1a22b7c11c36.1588347029.git.gitgitgadget@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <03b2c84db36754b321dd15cd8a9e1a22b7c11c36.1588347029.git.gitgitgadget@gmail.com> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Fri, May 01, 2020 at 03:30:20PM +0000, Derrick Stolee via GitGitGadget wrote: > From: Derrick Stolee > > In Documentation/technical/commit-graph-format.txt, the definition > of the BIDX chunk specifies the length is a number of 8-byte words. > During development we discovered that using 8-byte words in the > Murmur3 hash algorithm causes issues with Big-Endian versus Little- > Endian machines. Thus, the hash algorithm was adapted to work on a I'm nit-picking here, but I believe that "Little Endian" is usually spelled "little endian", right? At least, 'git log --oneline -Gendian | wc -l' doesn't return many/any results for me, but '-GEndian' does. > byte-by-byte basis. However, this caused a change in the definition > of a "word" in bloom.h. Now, a "word" is a single byte, which allows > filters to be as small as two bytes. These length-two filters are > demonstrated in t0095-bloom.sh, and a larger filter of length 25 is > demonstrated as well. > > The original point of using 8-byte words was for alignment reasons. > It also presented opportunities for extremely sparse Bloom filters > when there were a small number of changes at a commit, creating a > very low false-positive rate. However, modifying the format at this > point is unlikely to be a valuable exercise. Also, this use of > single-byte granularity does present opportunities to save space. > It is unclear if 8-byte alignment of the filters would present any > meaningful performance benefits. > > Modify the format document to reflect reality. > > Signed-off-by: Derrick Stolee The rest of this patch looks good, and indeed matches reality ;). Reviewed-by: Taylor Blau > --- > Documentation/technical/commit-graph-format.txt | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/Documentation/technical/commit-graph-format.txt b/Documentation/technical/commit-graph-format.txt > index de56f9f1efd..1beef171822 100644 > --- a/Documentation/technical/commit-graph-format.txt > +++ b/Documentation/technical/commit-graph-format.txt > @@ -97,10 +97,10 @@ CHUNK DATA: > bit on. The other bits correspond to the position of the last parent. > > Bloom Filter Index (ID: {'B', 'I', 'D', 'X'}) (N * 4 bytes) [Optional] > - * The ith entry, BIDX[i], stores the number of 8-byte word blocks in all > - Bloom filters from commit 0 to commit i (inclusive) in lexicographic > - order. The Bloom filter for the i-th commit spans from BIDX[i-1] to > - BIDX[i] (plus header length), where BIDX[-1] is 0. > + * The ith entry, BIDX[i], stores the number of bytes in all Bloom filters > + from commit 0 to commit i (inclusive) in lexicographic order. The Bloom > + filter for the i-th commit spans from BIDX[i-1] to BIDX[i] (plus header > + length), where BIDX[-1] is 0. > * The BIDX chunk is ignored if the BDAT chunk is not present. > > Bloom Filter Data (ID: {'B', 'D', 'A', 'T'}) [Optional] > -- > gitgitgadget Thanks, Taylor