[PATCH 0/3] optimize git-contacts

This patch series aims to make contrib/git-contacts faster by reducing
the number of expensive git-blame invocations it makes. It does so by
taking advantage of git-blame's new ability to accept multiple -L ranges
in a single invocation [1] (es/blame-L-twice in 'next').

Some numbers, given a randomly chosen range of commits:

  (before)
  % time git-contacts 25fba78d36be6297^..23c339c0f262aad2 >/dev/null
  real  0m6.142s
  user  0m5.429s
  sys   0m0.356s

  (after)
  % time git-contacts 25fba78d36be6297^..23c339c0f262aad2 >/dev/null
  real  0m2.285s
  user  0m2.093s
  sys   0m0.165s

[1]: http://thread.gmane.org/gmane.comp.version-control.git/231739

Eric Sunshine (3):
  contacts: validate hunk length earlier
  contacts: gather all blame sources prior to invoking git-blame
  contacts: reduce git-blame invocations

 contrib/contacts/git-contacts | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

-- 
1.8.4.rc2.460.ga591f4a

Rather than calling get_blame() with a zero-length hunk only to have it
rejected immediately, perform hunk-length validation earlier in order to
avoid calling get_blame() unnecessarily.

This is a preparatory step to simplify later patches which reduce the
number of git-blame invocations by collecting together all lines to
blame within a single file at a particular revision. By validating the
blame range early, the subsequent patch can more easily avoid adding
empty ranges at collection time.

Signed-off-by: Eric Sunshine <redacted>
---
 contrib/contacts/git-contacts | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/contrib/contacts/git-contacts b/contrib/contacts/git-contacts
index d80f7d1..4fbb2ef 100755
--- a/contrib/contacts/git-contacts
+++ b/contrib/contacts/git-contacts

@@ -60,8 +60,6 @@ sub import_commits {
 
 sub get_blame {
 	my ($commits, $source, $start, $len, $from) = @_;
-	$len = 1 unless defined($len);
-	return if $len == 0;
 	open my $f, '-|',
 		qw(git blame --porcelain -C), '-L', "$start,+$len",
 		'--since', $since, "$from^", '--', $source or die;

@@ -90,7 +88,8 @@ sub scan_patches {
 		} elsif (/^--- /) {
 			die "Cannot parse hunk source: $_\n";
 		} elsif (/^@@ -(\d+)(?:,(\d+))?/ && $source) {
-			get_blame($commits, $source, $1, $2, $id);
+			my $len = defined($2) ? $2 : 1;
+			get_blame($commits, $source, $1, $len, $id) if $len;
 		}
 	}
 }

-- 
1.8.4.rc2.460.ga591f4a

git-contacts invokes git-blame once for each patch hunk it encounters.
No attempt is made to consolidate invocations for multiple hunks
referencing the same file at the same revision. This can become
expensive quickly.

Reduce the number of git-blame invocations by taking advantage of the
ability to specify multiple -L ranges for a single invocation.

Without this patch, on a randomly chosen range of commits:

  % time git-contacts 25fba78d36be6297^..23c339c0f262aad2 >/dev/null
  real  0m6.142s
  user  0m5.429s
  sys   0m0.356s

With this patch:

  % time git-contacts 25fba78d36be6297^..23c339c0f262aad2 >/dev/null
  real  0m2.285s
  user  0m2.093s
  sys   0m0.165s

Signed-off-by: Eric Sunshine <redacted>
---
 contrib/contacts/git-contacts | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/contrib/contacts/git-contacts b/contrib/contacts/git-contacts
index b4d3526..fb6429b 100755
--- a/contrib/contacts/git-contacts
+++ b/contrib/contacts/git-contacts

@@ -59,9 +59,11 @@ sub import_commits {
 }
 
 sub get_blame {
-	my ($commits, $source, $start, $len, $from) = @_;
+	my ($commits, $source, $from, $ranges) = @_;
+	return unless @$ranges;
 	open my $f, '-|',
-		qw(git blame --porcelain -C), '-L', "$start,+$len",
+		qw(git blame --porcelain -C),
+		map({"-L$_->[0],+$_->[1]"} @$ranges),
 		'--since', $since, "$from^", '--', $source or die;
 	while (<$f>) {
 		if (/^([0-9a-f]{40}) \d+ \d+ \d+$/) {

@@ -78,10 +80,7 @@ sub blame_sources {
 	my ($sources, $commits) = @_;
 	for my $s (keys %$sources) {
 		for my $id (keys %{$sources->{$s}}) {
-			for my $range (@{$sources->{$s}{$id}}) {
-				get_blame($commits, $s,
-					  $range->[0], $range->[1], $id);
-			}
+			get_blame($commits, $s, $id, $sources->{$s}{$id});
 		}
 	}
 }

-- 
1.8.4.rc2.460.ga591f4a

git-contacts invokes git-blame immediately upon encountering a patch
hunk. No attempt is made to consolidate invocations for multiple hunks
referencing the same file at the same revision. This can become
expensive quickly.

Any effort to reduce the number of times git-blame is run will need to
to know in advance which line ranges to blame per file per revision.
Make this information available by collecting all sources as a distinct
step from invoking git-blame.  A subsequent patch will utilize the
information to optimize git-blame invocations.

Signed-off-by: Eric Sunshine <redacted>
---
 contrib/contacts/git-contacts | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/contrib/contacts/git-contacts b/contrib/contacts/git-contacts
index 4fbb2ef..b4d3526 100755
--- a/contrib/contacts/git-contacts
+++ b/contrib/contacts/git-contacts

@@ -74,8 +74,20 @@ sub get_blame {
 	close $f;
 }
 
+sub blame_sources {
+	my ($sources, $commits) = @_;
+	for my $s (keys %$sources) {
+		for my $id (keys %{$sources->{$s}}) {
+			for my $range (@{$sources->{$s}{$id}}) {
+				get_blame($commits, $s,
+					  $range->[0], $range->[1], $id);
+			}
+		}
+	}
+}
+
 sub scan_patches {
-	my ($commits, $id, $f) = @_;
+	my ($sources, $id, $f) = @_;
 	my $source;
 	while (<$f>) {
 		if (/^From ([0-9a-f]{40}) Mon Sep 17 00:00:00 2001$/) {

@@ -89,7 +101,7 @@ sub scan_patches {
 			die "Cannot parse hunk source: $_\n";
 		} elsif (/^@@ -(\d+)(?:,(\d+))?/ && $source) {
 			my $len = defined($2) ? $2 : 1;
-			get_blame($commits, $source, $1, $len, $id) if $len;
+			push @{$sources->{$source}{$id}}, [$1, $len] if $len;
 		}
 	}
 }

@@ -162,13 +174,16 @@ for (@ARGV) {
 	}
 }
 
-my %commits;
+my %sources;
 for (@files) {
-	scan_patch_file(\%commits, $_);
+	scan_patch_file(\%sources, $_);
 }
 if (@rev_args) {
-	scan_rev_args(\%commits, \@rev_args)
+	scan_rev_args(\%sources, \@rev_args)
 }
+
+my %commits;
+blame_sources(\%sources, \%commits);
 import_commits(\%commits);
 
 my $contacts = {};

-- 
1.8.4.rc2.460.ga591f4a