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From: "SZEDER Gábor" <szeder.dev@gmail.com>
To: git@vger.kernel.org
Cc: "Jeff King" <peff@peff.net>, "Junio C Hamano" <gitster@pobox.com>,
	"Derrick Stolee" <stolee@gmail.com>,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Stefan Beller" <sbeller@google.com>,
	"Duy Nguyen" <pclouds@gmail.com>,
	"SZEDER Gábor" <szeder.dev@gmail.com>
Subject: [PATCH 3/4] revision.c: use the Bloom filter to speed up path-limited revision walks
Date: Tue,  9 Oct 2018 21:34:44 +0200
Message-ID: <20181009193445.21908-4-szeder.dev@gmail.com> (raw)
In-Reply-To: <20181009193445.21908-1-szeder.dev@gmail.com>

When $GIT_USE_POC_BLOOM_FILTER is set to a non-empty value, the
revision walk will use the Bloom filter to speed up a path-limited
revision walk.

Load the Bloom filter in prepare_revision_walk(); probably not the
best place for it, but it should suffice for experiementing with 'git
rev-list'.

Checking the Bloom filter is plugged into rev_compare_tree(), the
function that compares the given paths in a commit to one of its
parents.  If checking the Bloom filter returns that the interesting
paths did not change, then it won't bother with the running the
expensive diff.

Add a new field to 'struct pathspec' to hold the SHA of the path, so
that hash is computed only once and then reused when checking each
commit.
---
 pathspec.h |  1 +
 revision.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+)

diff --git a/pathspec.h b/pathspec.h
index a6525a6551..565a26d91e 100644
--- a/pathspec.h
+++ b/pathspec.h
@@ -47,6 +47,7 @@ struct pathspec {
 			} match_mode;
 		} *attr_match;
 		struct attr_check *attr_check;
+		unsigned char name_hash[GIT_MAX_RAWSZ];
 	} *items;
 };
 
diff --git a/revision.c b/revision.c
index c5d0cb6599..3565785ca6 100644
--- a/revision.c
+++ b/revision.c
@@ -27,6 +27,7 @@
 #include "commit-reach.h"
 #include "commit-graph.h"
 #include "prio-queue.h"
+#include "bloom-filter.h"
 
 volatile show_early_output_fn_t show_early_output;
 
@@ -463,6 +464,62 @@ static void file_change(struct diff_options *options,
 	options->flags.has_changes = 1;
 }
 
+/* Another static... */
+static struct bloom_filter bf;
+
+static int check_maybe_different_in_bloom_filter(struct rev_info *revs,
+						 struct commit *parent,
+						 struct commit *commit)
+{
+	unsigned char p_c_hash[GIT_MAX_RAWSZ];
+	int i;
+
+	if (!bf.bits)
+		return -1;
+	/*
+	 * If a commit is not in the 'commit-graph' file, then it's not in
+	 * the Bloom filter either, so any query into that would report
+	 * back a false negative, which is unacceptable.
+	 *
+	 * The writer of the Bloom filter must ensure that all commits that
+	 * go into the 'commit-graph' go into the Bloom filter as well.
+	 *
+	 * If we won't tie the Bloom filter to the commit-graph tightly,
+	 * then we'll have to come up with another means to prevent such
+	 * false negatives.
+	 */
+	if (!the_repository->objects->commit_graph)
+		return -1;
+	if (commit->generation == GENERATION_NUMBER_INFINITY)
+		return -1;
+
+	hashxor(parent->object.oid.hash, commit->object.oid.hash, p_c_hash);
+
+	for (i = 0; i < revs->pruning.pathspec.nr; i++) {
+		struct pathspec_item *pi = &revs->pruning.pathspec.items[i];
+		unsigned char hash[GIT_MAX_RAWSZ];
+
+		hashxor(pi->name_hash, p_c_hash, hash);
+		if (bloom_filter_check_hash(&bf, hash)) {
+			/*
+			 * At least one of the interesting pathspecs differs,
+			 * so we can return early and let the diff machinery
+			 * make sure that they indeed differ.
+			 *
+			 * Note: the diff machinery will look at all the given
+			 * paths; a possible future optimization might bring
+			 * the Bloom filter and the diff machinery closer to
+			 * each other, so the diff won't waste time looking
+			 * at those paths that the Bloom filter have found
+			 * unchanged.
+			 */
+			return 1;
+		}
+	}
+
+	return 0;
+}
+
 static int rev_compare_tree(struct rev_info *revs,
 			    struct commit *parent, struct commit *commit)
 {
@@ -492,6 +549,9 @@ static int rev_compare_tree(struct rev_info *revs,
 			return REV_TREE_SAME;
 	}
 
+	if (!check_maybe_different_in_bloom_filter(revs, parent, commit))
+		return REV_TREE_SAME;
+
 	tree_difference = REV_TREE_SAME;
 	revs->pruning.flags.has_changes = 0;
 	if (diff_tree_oid(&t1->object.oid, &t2->object.oid, "",
@@ -3106,6 +3166,40 @@ static void expand_topo_walk(struct rev_info *revs, struct commit *commit)
 	}
 }
 
+void prepare_to_use_bloom_filter(struct rev_info *revs)
+{
+	const char *env = getenv("GIT_USE_POC_BLOOM_FILTER");
+	int i;
+
+	if (!env || !*env)
+		return;
+
+	for (i = 0; i < revs->pruning.pathspec.nr; i++) {
+		struct pathspec_item *pi = &revs->pruning.pathspec.items[i];
+		const char *path = pi->match;
+		git_hash_ctx ctx;
+		size_t len = strlen(path);
+
+		/*
+		 * TODO: What about wildcards?  We'd probably just want to
+		 * ignore the Bloom filter then.
+		 */
+		the_hash_algo->init_fn(&ctx);
+		the_hash_algo->update_fn(&ctx, path,
+					 path[len - 1] == '/' ? len - 1 : len);
+		the_hash_algo->final_fn(pi->name_hash, &ctx);
+	}
+
+	if (bf.bits)
+		/* Already loaded. */
+		return;
+
+	if (bloom_filter_load(&bf) < 0) {
+		warning("you wanted to use the Bloom filter, but it couldn't be loaded");
+		return;
+	}
+}
+
 int prepare_revision_walk(struct rev_info *revs)
 {
 	int i;
@@ -3155,6 +3249,9 @@ int prepare_revision_walk(struct rev_info *revs)
 		simplify_merges(revs);
 	if (revs->children.name)
 		set_children(revs);
+
+	prepare_to_use_bloom_filter(revs);
+
 	return 0;
 }
 
-- 
2.19.1.409.g0a0ee5eb6b


  parent reply index

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-03 13:23 We should add a "git gc --auto" after "git clone" due to commit graph Ævar Arnfjörð Bjarmason
2018-10-03 13:36 ` SZEDER Gábor
2018-10-03 13:42   ` Derrick Stolee
2018-10-03 14:18     ` Ævar Arnfjörð Bjarmason
2018-10-03 14:01   ` Ævar Arnfjörð Bjarmason
2018-10-03 14:17     ` SZEDER Gábor
2018-10-03 14:22       ` Ævar Arnfjörð Bjarmason
2018-10-03 14:53         ` SZEDER Gábor
2018-10-03 15:19           ` Ævar Arnfjörð Bjarmason
2018-10-03 16:59             ` SZEDER Gábor
2018-10-05  6:09               ` Junio C Hamano
2018-10-10 22:07                 ` SZEDER Gábor
2018-10-10 23:01                   ` Ævar Arnfjörð Bjarmason
2018-10-03 19:08           ` Stefan Beller
2018-10-03 19:21             ` Jeff King
2018-10-03 20:35               ` Ævar Arnfjörð Bjarmason
2018-10-03 17:47         ` Stefan Beller
2018-10-03 18:47           ` Ævar Arnfjörð Bjarmason
2018-10-03 18:51             ` Jeff King
2018-10-03 18:59               ` Derrick Stolee
2018-10-03 19:18                 ` Jeff King
2018-10-08 16:41                   ` SZEDER Gábor
2018-10-08 16:57                     ` Derrick Stolee
2018-10-08 18:10                       ` SZEDER Gábor
2018-10-08 18:29                         ` Derrick Stolee
2018-10-09  3:08                           ` Jeff King
2018-10-09 13:48                             ` Bloom Filters (was Re: We should add a "git gc --auto" after "git clone" due to commit graph) Derrick Stolee
2018-10-09 18:45                               ` Ævar Arnfjörð Bjarmason
2018-10-09 18:46                               ` Jeff King
2018-10-09 19:03                                 ` Derrick Stolee
2018-10-09 21:14                                   ` Jeff King
2018-10-09 23:12                                     ` Bloom Filters Jeff King
2018-10-09 23:13                                       ` [PoC -- do not apply 1/3] initial tree-bitmap proof of concept Jeff King
2018-10-09 23:14                                       ` [PoC -- do not apply 2/3] test-tree-bitmap: add "dump" mode Jeff King
2018-10-10  0:48                                         ` Junio C Hamano
2018-10-11  3:13                                           ` Jeff King
2018-10-09 23:14                                       ` [PoC -- do not apply 3/3] test-tree-bitmap: replace ewah with custom rle encoding Jeff King
2018-10-10  0:58                                         ` Junio C Hamano
2018-10-11  3:20                                           ` Jeff King
2018-10-11 12:33                                       ` Bloom Filters Derrick Stolee
2018-10-11 13:43                                         ` Jeff King
2018-10-09 21:30                             ` We should add a "git gc --auto" after "git clone" due to commit graph SZEDER Gábor
2018-10-09 19:34                       ` [PATCH 0/4] Bloom filter experiment SZEDER Gábor
2018-10-09 19:34                         ` [PATCH 1/4] Add a (very) barebones Bloom filter implementation SZEDER Gábor
2018-10-09 19:34                         ` [PATCH 2/4] commit-graph: write a Bloom filter containing changed paths for each commit SZEDER Gábor
2018-10-09 21:06                           ` Jeff King
2018-10-09 21:37                             ` SZEDER Gábor
2018-10-09 19:34                         ` SZEDER Gábor [this message]
2018-10-09 19:34                         ` [PATCH 4/4] revision.c: add GIT_TRACE_BLOOM_FILTER for a bit of statistics SZEDER Gábor
2018-10-09 19:47                         ` [PATCH 0/4] Bloom filter experiment Derrick Stolee
2018-10-11  1:21                         ` [PATCH 0/2] Per-commit filter proof of concept Jonathan Tan
2018-10-11  1:21                           ` [PATCH 1/2] One filter per commit Jonathan Tan
2018-10-11  1:21                           ` [PATCH 2/2] Only make bloom filter for first parent Jonathan Tan
2018-10-11  7:37                           ` [PATCH 0/2] Per-commit filter proof of concept Ævar Arnfjörð Bjarmason
2018-10-15 14:39                         ` [PATCH 0/4] Bloom filter experiment Derrick Stolee
2018-10-16  4:45                           ` Junio C Hamano
2018-10-16 11:13                             ` Derrick Stolee
2018-10-16 12:57                               ` Ævar Arnfjörð Bjarmason
2018-10-16 13:03                                 ` Derrick Stolee
2018-10-18  2:00                                 ` Junio C Hamano
2018-10-16 23:41                           ` Jonathan Tan
2018-10-08 23:02                     ` We should add a "git gc --auto" after "git clone" due to commit graph Junio C Hamano
2018-10-03 14:32     ` Duy Nguyen
2018-10-03 16:45 ` Duy Nguyen
2018-10-04 21:42 ` [RFC PATCH] " Ævar Arnfjörð Bjarmason
2018-10-05 12:05   ` Derrick Stolee
2018-10-05 13:05     ` Ævar Arnfjörð Bjarmason
2018-10-05 13:45       ` Derrick Stolee
2018-10-05 14:04         ` Ævar Arnfjörð Bjarmason
2018-10-05 19:21         ` Jeff King
2018-10-05 19:41           ` Derrick Stolee
2018-10-05 19:47             ` Jeff King
2018-10-05 20:00               ` Derrick Stolee
2018-10-05 20:02                 ` Jeff King
2018-10-05 20:01               ` Ævar Arnfjörð Bjarmason
2018-10-05 20:09                 ` Jeff King
2018-10-11 12:49 [PATCH 1/2] One filter per commit Derrick Stolee
2018-10-11 19:11 ` [PATCH] Per-commit and per-parent filters for 2 parents Jonathan Tan

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