Re: [PATCH 4/8] git-remote-mediawiki: get rid of O(N^2) loop
From: Junio C Hamano <hidden>
Date: 2016-06-15 22:54:16
Matthieu Moy [off-list ref] writes:
The algorithm to find a path from the local revision to the remote one was calling "git rev-list" and parsing its output N times. Run rev-list only once, and fill a hashtable with the result to optimize the body of the loop.
Good thinking. I wonder if it would further reduce the overhead if you stop using --children and do this using --parents instead, as you will be reading the parsed_sha1..local range either way yourself anyway.
quoted hunk
Signed-off-by: Matthieu Moy <redacted> --- contrib/mw-to-git/git-remote-mediawiki | 25 ++++++++++++++++++------- 1 file changed, 18 insertions(+), 7 deletions(-)diff --git a/contrib/mw-to-git/git-remote-mediawiki b/contrib/mw-to-git/git-remote-mediawiki index 8e46e4e..f9c0cc6 100755 --- a/contrib/mw-to-git/git-remote-mediawiki +++ b/contrib/mw-to-git/git-remote-mediawiki@@ -1196,16 +1196,27 @@ sub mw_push_revision { if ($last_local_revid > 0) { my $parsed_sha1 = $remoteorigin_sha1; # Find a path from last MediaWiki commit to pushed commit + print STDERR "Computing path from local to remote ...\n"; + my @local_ancestry = split(/\n/, run_git("rev-list --boundary --children $local ^$parsed_sha1")); + my %local_ancestry; + foreach my $line (@local_ancestry) { + if (my ($parent, $child) = $line =~ m/^-?([a-f0-9]+) ([a-f0-9]+)/) { + $local_ancestry{$parent} = $child; + if ($parent eq $parsed_sha1 || $child eq $parsed_sha1) { + print STDERR "$parent -> $child\n"; + } + } elsif (!$line =~ m/^([a-f0-9]+)/) { + die "Unexpected output from git rev-list: $line"; + } + } while ($parsed_sha1 ne $HEAD_sha1) { - my @commit_info = grep(/^$parsed_sha1/, split(/\n/, run_git("rev-list --children $local"))); - if (!@commit_info) { + my $child = $local_ancestry{$parsed_sha1}; + if (!$child) { + printf STDERR "Cannot find a path in history from remote commit to last commit\n"; return error_non_fast_forward($remote); } - my @commit_info_split = split(/ |\n/, $commit_info[0]); - # $commit_info_split[1] is the sha1 of the commit to export - # $commit_info_split[0] is the sha1 of its direct child - push(@commit_pairs, \@commit_info_split); - $parsed_sha1 = $commit_info_split[1]; + push(@commit_pairs, [$parsed_sha1, $child]); + $parsed_sha1 = $child; } } else { # No remote mediawiki revision. Export the whole