patchgit-svn: cache max revision in rev_db databases

> Signed-off-by: Sam Vilain <sam@vilain.net>
> ---
>  git-svn.perl |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/git-svn.perl b/git-svn.perl
> index 610563c..c9758a0 100755
> --- a/git-svn.perl
> +++ b/git-svn.perl
> @@ -804,6 +804,7 @@ sub working_head_info {
>  	my ($head, $refs) = @_;
>  	my ($fh, $ctx) = command_output_pipe('log', $head);
>  	my $hash;
> +	my %max;
>  	while (<$fh>) {
>  		if ( m{^commit ($::sha1)$} ) {
>  			$hash = $1;
> @@ -812,11 +813,14 @@ sub working_head_info {
>  		next unless s{^\s+(git-svn-id:)}{$1};
>  		my ($url, $rev, $uuid) = extract_metadata($_);
>  		if (defined $url && defined $rev) {
> +			next if $max{$url} and $max{$url} < $rev;
>  			if (my $gs = Git::SVN->find_by_url($url)) {
>  				my $c = $gs->rev_db_get($rev);
>  				if ($c && $c eq $hash) {
>  					close $fh; # break the pipe
>  					return ($url, $rev, $uuid, $gs);
> +				} else {
> +					$max{$url} ||= $gs->rev_db_max;
>  				}
>  			}
>  		}

> Sam Vilain <sam@vilain.net> wrote:
>   
>> Cache the maximum revision for each rev_db URL rather than looking it
>> up each time.  This saves a lot of time when rebuilding indexes on a
>> freshly cloned repository.
>>     
>
> It looks correct, but I'm not sure how often we can even hit this
> optimization to make it worth it.
>
> Any live repositories and benchmarks you've run this on?
> (without the rev-list => log patch applied, which would be a big
> performance improvement if all log messages were under 16k).
>