[PATCH] git-svn: Make it scream by minimizing temp files

[Marcus Griep <marcus@griep.us>]

Currently, git-svn would create a temp file on four occasions:
1. Reading a blob out of the object db
2. Creating a delta from svn
3. Hashing and writing a blob into the object db
4. Reading a blob out of the object db (in another place in code)

Any time git-svn did the above, it would dutifully create and then
delete said temp file.  Unfortunately, this means that between 2-4
temporary files are created/deleted per file 'add/modify'-ed in
svn (O(n)).  This causes significant overhead and helps the inode
counter to spin beautifully.

By its nature, git-svn is a serial beast.  Thus, reusing a temp file
does not pose significant problems.  "truncate and seek" takes much
less time than "unlink and create".  This patch centralizes the
tempfile creation and holds onto the tempfile until they are deleted
on exit.  This significantly reduces file overhead, now requiring
at most three (3) temp files per run (O(1)).

Signed-off-by: Marcus Griep <marcus@griep.us>
---
 git-svn.perl |   48 ++++++++++++++++++++++++++++++------------------
 1 files changed, 30 insertions(+), 18 deletions(-)

diff --git a/git-svn.perl b/git-svn.perl
index 5099c1f..02ae207 100755
--- a/git-svn.perl
+++ b/git-svn.perl
@@ -1257,7 +1257,7 @@ sub md5sum {
 	my $arg = shift;
 	my $ref = ref $arg;
 	my $md5 = Digest::MD5->new();
-        if ($ref eq 'GLOB' || $ref eq 'IO::File') {
+        if ($ref eq 'GLOB' || $ref eq 'IO::File' || $ref eq 'File::Temp') {
 		$md5->addfile($arg) or croak $!;
 	} elsif ($ref eq 'SCALAR') {
 		$md5->add($$arg) or croak $!;
@@ -1282,6 +1282,8 @@ use Carp qw/croak/;
 use File::Path qw/mkpath/;
 use File::Copy qw/copy/;
 use IPC::Open3;
+use File::Temp qw/ :seekable /;
+use File::Spec;
 
 my ($_gc_nr, $_gc_period);
 
@@ -1320,10 +1322,11 @@ BEGIN {
 	}
 }
 
-my (%LOCKFILES, %INDEX_FILES);
+my (%LOCKFILES, %INDEX_FILES, %TEMP_FILES);
 END {
 	unlink keys %LOCKFILES if %LOCKFILES;
 	unlink keys %INDEX_FILES if %INDEX_FILES;
+	unlink values %TEMP_FILES if %TEMP_FILES;
 }
 
 sub resolve_local_globs {
@@ -2932,6 +2935,23 @@ sub remove_username {
 	$_[0] =~ s{^([^:]*://)[^@]+@}{$1};
 }
 
+sub _temp_file {
+	my ($self, $fd, $autoflush) = @_;
+	if (defined $TEMP_FILES{$fd}) {
+		truncate $TEMP_FILES{$fd}, 0 or croak $!;
+		seek $TEMP_FILES{$fd}, 0, 0 or croak $!;
+	} else {
+		$TEMP_FILES{$fd} = File::Temp->new(
+									TEMPLATE => 'GitSvn_XXXXXX',
+									DIR => File::Spec->tmpdir
+									) or croak $!;
+		if (defined $autoflush) {
+			$TEMP_FILES{$fd}->autoflush($autoflush);
+		}
+	}
+	$TEMP_FILES{$fd};
+}
+
 package Git::SVN::Prompt;
 use strict;
 use warnings;
@@ -3222,13 +3242,11 @@ sub change_file_prop {
 
 sub apply_textdelta {
 	my ($self, $fb, $exp) = @_;
-	my $fh = IO::File->new_tmpfile;
-	$fh->autoflush(1);
+	my $fh = Git::SVN->_temp_file('delta_temp', 1);
 	# $fh gets auto-closed() by SVN::TxDelta::apply(),
 	# (but $base does not,) so dup() it for reading in close_file
 	open my $dup, '<&', $fh or croak $!;
-	my $base = IO::File->new_tmpfile;
-	$base->autoflush(1);
+	my $base = Git::SVN->_temp_file('git_blob_temp', 1);
 	if ($fb->{blob}) {
 		print $base 'link ' if ($fb->{mode_a} == 120000);
 		my $size = $::_repository->cat_blob($fb->{blob}, $base);
@@ -3243,9 +3261,9 @@ sub apply_textdelta {
 		}
 	}
 	seek $base, 0, 0 or croak $!;
-	$fb->{fh} = $dup;
+	$fb->{fh} = $fh;
 	$fb->{base} = $base;
-	[ SVN::TxDelta::apply($base, $fh, undef, $fb->{path}, $fb->{pool}) ];
+	[ SVN::TxDelta::apply($base, $dup, undef, $fb->{path}, $fb->{pool}) ];
 }
 
 sub close_file {
@@ -3274,22 +3292,18 @@ sub close_file {
 			}
 		}
 
-		my ($tmp_fh, $tmp_filename) = File::Temp::tempfile(UNLINK => 1);
+		my $tmp_fh = Git::SVN->_temp_file('hash_temp');
 		my $result;
 		while ($result = sysread($fh, my $string, 1024)) {
 			my $wrote = syswrite($tmp_fh, $string, $result);
 			defined($wrote) && $wrote == $result
-				or croak("write $tmp_filename: $!\n");
+				or croak("write $tmp_fh->filename: $!\n");
 		}
 		defined $result or croak $!;
-		close $tmp_fh or croak $!;
 
-		close $fh or croak $!;
 
-		$hash = $::_repository->hash_and_insert_object($tmp_filename);
-		unlink($tmp_filename);
+		$hash = $::_repository->hash_and_insert_object($tmp_fh->filename);
 		$hash =~ /^[a-f\d]{40}$/ or die "not a sha1: $hash\n";
-		close $fb->{base} or croak $!;
 	} else {
 		$hash = $fb->{blob} or die "no blob information\n";
 	}
@@ -3659,7 +3673,7 @@ sub chg_file {
 	} elsif ($m->{mode_b} !~ /755$/ && $m->{mode_a} =~ /755$/) {
 		$self->change_file_prop($fbat,'svn:executable',undef);
 	}
-	my $fh = IO::File->new_tmpfile or croak $!;
+	my $fh = Git::SVN->_temp_file('git_blob_temp');
 	if ($m->{mode_b} =~ /^120/) {
 		print $fh 'link ' or croak $!;
 		$self->change_file_prop($fbat,'svn:special','*');
@@ -3679,8 +3693,6 @@ sub chg_file {
 	my $got = SVN::TxDelta::send_stream($fh, @$atd, $pool);
 	die "Checksum mismatch\nexpected: $exp\ngot: $got\n" if ($got ne $exp);
 	$pool->clear;
-
-	close $fh or croak $!;
 }
 
 sub D {
-- 
1.6.0.rc2.4.g39f8