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,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 5FF521F4B4 for ; Thu, 10 Sep 2020 19:22:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726741AbgIJTUg (ORCPT ); Thu, 10 Sep 2020 15:20:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40758 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731456AbgIJPwh (ORCPT ); Thu, 10 Sep 2020 11:52:37 -0400 Received: from mail-qk1-x743.google.com (mail-qk1-x743.google.com [IPv6:2607:f8b0:4864:20::743]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A8DD3C061757 for ; Thu, 10 Sep 2020 08:45:21 -0700 (PDT) Received: by mail-qk1-x743.google.com with SMTP id f142so6473370qke.13 for ; Thu, 10 Sep 2020 08:45:21 -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=Re8J5oxIIDDWMFwtUbjxoXenzLIFTVRDjPc7LWKOyrI=; b=oM6IUJRBAvoQ6kCQq3TkQBFye5NQAFUTpG5WWgmj3hguvfF8+ptHnTI88bRw7Sjk8w +6+Posep8xWCosvPNN339sm5yoM+ysfnbVsAgbiIhjHi86bYU1cFtv63R5HNPBZCH9ih QDl18t0lV3ZYpS38Gmwzpn2FuOYRdG3IkVZ5pWu1Qwb5iDD8gX2aL0RxDFd5lqaJRy0Q wzvGzCCJqkklomX1TnTu9LFNTJu/KzBQkbvQe8HjJbmWsj2Z/VdG+LkbvF0txo9geEh4 SXwvceDJtpIzNOS+7WTTQasD2fkWJ+V0/z8jZTzVWyewDngDIXVSOlDvuqFOROHFNei0 MGeA== 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=Re8J5oxIIDDWMFwtUbjxoXenzLIFTVRDjPc7LWKOyrI=; b=KzFDKSY6o1+ycfx8thfW4Nyx2is2CWHuP+SO/AdoKls7gEw+2fSygdgDoJ8J1rZMaX xldahZZNa8OFtOYKaWUHN6P0pnzpreo0GpNfaq4UW6BDaat0GOeeueD7+aPJnYnWVAUP A8IORL5wTSOEFnwZLMYQHNWsBnFwuMamSC59lvR8EwwW71C8QcQvnkJXz9T0eAD6RXrx uhaTo0E0S0iySGzY8k0yarPHuf/soneH+hZO4W03PIH2GtppScb0Aweb4cA8M5QFHI2e ki2UjcvKcuedMV0GuW30tXtQO3UXwEH2C9EuZP3hsKe1QZZU61cxY/L9KAXBaam6Nbui z6Jg== X-Gm-Message-State: AOAM532RavFN2pP7FjmxYkEReEaFDDPVSdnZkj7beucdOfy92mRBchCW JEQHeRRy5blhcczM/YuuGXyvDZMLldGyiwZY X-Google-Smtp-Source: ABdhPJxaIJbCULQqUcrVvZMy5mppEMKsvVqUi3e8RgenSFagcStuLBFOpQlqF/dznBN08caOO52R/w== X-Received: by 2002:a05:620a:a52:: with SMTP id j18mr7978598qka.445.1599752719994; Thu, 10 Sep 2020 08:45:19 -0700 (PDT) Received: from localhost ([2605:9480:22e:ff10:b02c:9c0a:1a83:70bb]) by smtp.gmail.com with ESMTPSA id d12sm6506471qka.34.2020.09.10.08.45.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Sep 2020 08:45:19 -0700 (PDT) Date: Thu, 10 Sep 2020 11:45:16 -0400 From: Taylor Blau To: git@vger.kernel.org Cc: dstolee@microsoft.com, gitster@pobox.com, peff@peff.net, szeder.dev@gmail.com Subject: Re: [PATCH 10/12] bloom: encode out-of-bounds filters as non-empty Message-ID: <20200910154516.GA32117@nand.local> References: <1c993b83980e77594b0de2b1884cbc4cf484f9ab.1599664389.git.me@ttaylorr.com> <20200910033557.GA2178@nand.local> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200910033557.GA2178@nand.local> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Wed, Sep 09, 2020 at 11:35:57PM -0400, Taylor Blau wrote: > On Wed, Sep 09, 2020 at 11:23:48AM -0400, Taylor Blau wrote: > > - filter->data = NULL; > > - filter->len = 0; > > + filter->data = xmalloc(1); > > + filter->data[0] = 0xFF; > > + filter->len = 1; > > > > if (computed) > > *computed |= BLOOM_TRUNC_LARGE; > > Oops, I missed the case that added by the previous patch where the > number of diff entries is smaller than the limit, but the hashmap > entries (after directories are added and such) crosses the threshold. > > Specifically, this patch doesn't write the 0xFF filter like it should. > I'll send a different version of this patch tomorrow. This one should do the trick. Let's use it instead. --- >8 --- Subject: [PATCH] bloom: encode out-of-bounds filters as non-empty When a changed-path Bloom filter has either zero, or more than a certain number (commonly 512) of entries, the commit-graph machinery encodes it as "missing". More specifically, it sets the indices adjacent in the BIDX chunk as equal to each other to indicate a "length 0" filter; that is, that the filter occupies zero bytes on disk. This has heretofore been fine, since the commit-graph machinery has no need to care about these filters with too few or too many changed paths. Both cases act like no filter has been generated at all, and so there is no need to store them. In a subsequent commit, however, the commit-graph machinery will learn to only compute Bloom filters for some commits in the current commit-graph layer. This is a change from the current implementation which computes Bloom filters for all commits that are in the layer being written. Critically for this patch, only computing some of the Bloom filters means adding a third state for length 0 Bloom filters: zero entries, too many entries, or "hasn't been computed". It will be important for that future patch to distinguish between "not representable" (i.e., zero or too-many changed paths), and "hasn't been computed". In particular, we don't want to waste time recomputing filters that have already been computed. To that end, change how we store Bloom filters in the "computed but not representable" category: - Bloom filters with no entries are stored as a single byte with all bits low (i.e., all queries to that Bloom filter will return "definitely not") - Bloom filters with too many entries are stored as a single byte with all bits set high (i.e., all queries to that Bloom filter will return "maybe"). These rules are sufficient to not incur a behavior change by changing the on-disk representation of these two classes. Likewise, no specification changes are necessary for the commit-graph format, either: - Filters that were previously empty will be recomputed and stored according to the new rules, and - old clients reading filters generated by new clients will interpret the filters correctly and be none the wiser to how they were generated. Clients will invoke the Bloom machinery in more cases than before, but this can be addressed by returning a NULL filter when all bits are set high. This can be addressed in a future patch. Finally, note that this does increase the size of on-disk commit-graphs, but far less than other proposals. In particular, this is generally more efficient than storing a bitmap for which commits haven't computed their Bloom filters. Storing a bitmap incurs a penalty of one bit per commit, whereas storing explicit filters as above incurs a penalty of one byte per too-large or too-small commit. In practice, these boundary commits likely occupy a small proportion of the overall number of commits, and so the size penalty is likely smaller than storing a bitmap for all commits. A test to exercise filters which contain too many changed path entries will be introduced in a subsequent patch. Suggested-by: SZEDER Gábor Suggested-by: Jakub Narębski Helped-by: Derrick Stolee Signed-off-by: Taylor Blau --- .../technical/commit-graph-format.txt | 2 +- bloom.c | 16 ++++++++++++-- bloom.h | 1 + commit-graph.c | 5 +++++ t/t0095-bloom.sh | 8 +++---- t/t4216-log-bloom.sh | 21 +++++++++++++++++-- 6 files changed, 44 insertions(+), 9 deletions(-) diff --git a/Documentation/technical/commit-graph-format.txt b/Documentation/technical/commit-graph-format.txt index 6ddbceba15..6585f1948a 100644 --- a/Documentation/technical/commit-graph-format.txt +++ b/Documentation/technical/commit-graph-format.txt @@ -125,7 +125,7 @@ CHUNK DATA: * The rest of the chunk is the concatenation of all the computed Bloom filters for the commits in lexicographic order. * Note: Commits with no changes or more than 512 changes have Bloom filters - of length zero. + of length one, with either all bits set to zero or one respectively. * The BDAT chunk is present if and only if BIDX is present. Base Graphs List (ID: {'B', 'A', 'S', 'E'}) [Optional] diff --git a/bloom.c b/bloom.c index db9fb82437..d24747a1d5 100644 --- a/bloom.c +++ b/bloom.c @@ -177,6 +177,13 @@ static int pathmap_cmp(const void *hashmap_cmp_fn_data, return strcmp(e1->path, e2->path); } +static void init_truncated_large_filter(struct bloom_filter *filter) +{ + filter->data = xmalloc(1); + filter->data[0] = 0xFF; + filter->len = 1; +} + struct bloom_filter *get_or_compute_bloom_filter(struct repository *r, struct commit *c, int compute_if_not_present, @@ -260,12 +267,18 @@ struct bloom_filter *get_or_compute_bloom_filter(struct repository *r, } if (hashmap_get_size(&pathmap) > settings->max_changed_paths) { + init_truncated_large_filter(filter); if (computed) *computed |= BLOOM_TRUNC_LARGE; goto cleanup; } filter->len = (hashmap_get_size(&pathmap) * settings->bits_per_entry + BITS_PER_WORD - 1) / BITS_PER_WORD; + if (!filter->len) { + if (computed) + *computed |= BLOOM_TRUNC_SMALL; + filter->len = 1; + } filter->data = xcalloc(filter->len, sizeof(unsigned char)); hashmap_for_each_entry(&pathmap, &iter, e, entry) { @@ -279,8 +292,7 @@ struct bloom_filter *get_or_compute_bloom_filter(struct repository *r, } else { for (i = 0; i < diff_queued_diff.nr; i++) diff_free_filepair(diff_queued_diff.queue[i]); - filter->data = NULL; - filter->len = 0; + init_truncated_large_filter(filter); if (computed) *computed |= BLOOM_TRUNC_LARGE; diff --git a/bloom.h b/bloom.h index c6d77e8393..70a8840896 100644 --- a/bloom.h +++ b/bloom.h @@ -93,6 +93,7 @@ enum bloom_filter_computed { BLOOM_NOT_COMPUTED = (1 << 0), BLOOM_COMPUTED = (1 << 1), BLOOM_TRUNC_LARGE = (1 << 2), + BLOOM_TRUNC_SMALL = (1 << 3), }; struct bloom_filter *get_or_compute_bloom_filter(struct repository *r, diff --git a/commit-graph.c b/commit-graph.c index 500f29525a..d402743e61 100644 --- a/commit-graph.c +++ b/commit-graph.c @@ -974,6 +974,7 @@ struct write_commit_graph_context { int count_bloom_filter_computed; int count_bloom_filter_not_computed; + int count_bloom_filter_trunc_small; int count_bloom_filter_trunc_large; }; @@ -1405,6 +1406,8 @@ static void trace2_bloom_filter_write_statistics(struct write_commit_graph_conte ctx->count_bloom_filter_computed); jw_object_intmax(&jw, "filter_not_computed", ctx->count_bloom_filter_not_computed); + jw_object_intmax(&jw, "filter_trunc_small", + ctx->count_bloom_filter_trunc_small); jw_object_intmax(&jw, "filter_trunc_large", ctx->count_bloom_filter_trunc_large); jw_end(&jw); @@ -1446,6 +1449,8 @@ static void compute_bloom_filters(struct write_commit_graph_context *ctx) &computed); if (computed & BLOOM_COMPUTED) { ctx->count_bloom_filter_computed++; + if (computed & BLOOM_TRUNC_SMALL) + ctx->count_bloom_filter_trunc_small++; if (computed & BLOOM_TRUNC_LARGE) ctx->count_bloom_filter_trunc_large++; } else if (computed & BLOOM_NOT_COMPUTED) diff --git a/t/t0095-bloom.sh b/t/t0095-bloom.sh index 232ba2c485..7e4ab1795f 100755 --- a/t/t0095-bloom.sh +++ b/t/t0095-bloom.sh @@ -71,8 +71,8 @@ test_expect_success 'get bloom filters for commit with no changes' ' git init && git commit --allow-empty -m "c0" && cat >expect <<-\EOF && - Filter_Length:0 - Filter_Data: + Filter_Length:1 + Filter_Data:00| EOF test-tool bloom get_filter_for_commit "$(git rev-parse HEAD)" >actual && test_cmp expect actual @@ -107,8 +107,8 @@ test_expect_success EXPENSIVE 'get bloom filter for commit with 513 changes' ' git add bigDir && git commit -m "commit with 513 changes" && cat >expect <<-\EOF && - Filter_Length:0 - Filter_Data: + Filter_Length:1 + Filter_Data:ff| EOF test-tool bloom get_filter_for_commit "$(git rev-parse HEAD)" >actual && test_cmp expect actual diff --git a/t/t4216-log-bloom.sh b/t/t4216-log-bloom.sh index f375e752cd..a56327ffd4 100755 --- a/t/t4216-log-bloom.sh +++ b/t/t4216-log-bloom.sh @@ -30,6 +30,7 @@ test_expect_success 'setup test - repo, commits, commit graph, log outputs' ' rm file_to_be_deleted && git add . && git commit -m "file removed" && + git commit --allow-empty -m "empty" && git commit-graph write --reachable --changed-paths && test_oid_cache <<-EOF @@ -49,7 +50,7 @@ graph_read_expect () { } test_expect_success 'commit-graph write wrote out the bloom chunks' ' - graph_read_expect 15 + graph_read_expect 16 ' # Turn off any inherited trace2 settings for this test. @@ -156,7 +157,7 @@ test_expect_success 'setup - add commit-graph to the chain with Bloom filters' ' test_bloom_filters_used_when_some_filters_are_missing () { log_args=$1 - bloom_trace_prefix="statistics:{\"filter_not_present\":3,\"maybe\":6,\"definitely_not\":8" + bloom_trace_prefix="statistics:{\"filter_not_present\":3,\"maybe\":6,\"definitely_not\":9" setup "$log_args" && grep -q "$bloom_trace_prefix" "$TRASH_DIRECTORY/trace.perf" && test_cmp log_wo_bloom log_w_bloom @@ -271,4 +272,20 @@ test_expect_success 'correctly report changes over limit' ' ) ' +test_expect_success 'correctly report commits with no changed paths' ' + git init small && + test_when_finished "rm -fr small" && + ( + cd small && + + git commit --allow-empty -m "initial commit" && + + GIT_TRACE2_EVENT="$(pwd)/trace" \ + git commit-graph write --reachable --changed-paths && + grep "\"filter_computed\":1" trace && + grep "\"filter_trunc_small\":1" trace && + grep "\"filter_trunc_large\":0" trace + ) +' + test_done -- 2.27.0.2918.g22f69e1f31