[PATCHv2 1/4 (resent)] gitweb: Load checking
- From
Jakub Narebski <jnareb@gmail.com>
- Date
- Jan 3, 2010, 16:07 UTC
- Message-ID
- <1262534850-24572-2-git-send-email-jnareb@gmail.com>
- In-Reply-To
- <1262534850-24572-1-git-send-email-jnareb@gmail.com>
From: John 'Warthog9' Hawley <warthog9@kernel.org>
This changes slightly the behavior of gitweb, so that it verifies that the box isn't inundated with before attempting to serve gitweb. If the box is overloaded, it basically returns a 503 Server Unavailable until the load falls below the defined threshold. This helps dramatically if you have a box that's I/O bound, reaches a certain load and you don't want gitweb, the I/O hog that it is, increasing the pain the server is already undergoing.
This behavior is controlled by $maxload configuration variable. Default is a load of 300, which for most cases should never be hit. Unset it (set it to undefined value, i.e. undef) to turn off checking.
Currently it requires that '/proc/loadavg' file exists, otherwise the load check is bypassed (load is taken to be 0). So platforms that do not implement '/proc/loadavg' currently cannot use this feature.
Signed-off-by: John 'Warthog9' Hawley <warthog9@kernel.org> Signed-off-by: Jakub Narebski <jnareb@gmail.com> --- Originally appeared in http://permalink.gmane.org/gmane.comp.version-control.git/135418
Differences to original version by John 'Warthog9' Hawley (J.H.): * Slightly improved wording in commit message and in comments * $maxload is described in "Gitweb config file variables section in gitweb/README * You can use '$maxload = undef;' to turn off load checking * Error page for too high load is generated using die_error, which had to be extended to handle 503 Service Unavailable HTTP error code
One complaints that didn't get addressed was describing alternate approaches to just reading '/proc/loadavg', like using BSD::getloadavg module from CPAN, either in comments in gitweb.perl or in commit message. But I have changed my mind since then about this issue, and now I think it is not strictly necessary. I think that limitations of current approach are described in sufficient detail, and we have fall back for when used method cannot work.
gitweb/README | 7 ++++++- gitweb/gitweb.perl | 39 +++++++++++++++++++++++++++++++++++---- 2 files changed, 41 insertions(+), 5 deletions(-)
diff --git a/gitweb/README b/gitweb/README index e34ee79..6c2c8e1 100644 --- a/gitweb/README +++ b/gitweb/README @@ -174,7 +174,7 @@ not include variables usually directly set during build): Base URL for relative URLs in pages generated by gitweb, (e.g. $logo, $favicon, @stylesheets if they are relative URLs), needed and used only for URLs with nonempty PATH_INFO via - <base href="$base_url>. Usually gitweb sets its value correctly, + <base href="$base_url">. Usually gitweb sets its value correctly, and there is no need to set this variable, e.g. to $my_uri or "/". * $home_link Target of the home link on top of all pages (the first part of view @@ -228,6 +228,11 @@ not include variables usually directly set during build): repositories from launching cross-site scripting (XSS) attacks. Set this to true if you don't trust the content of your repositories. The default is false. + * $maxload + Used to set the maximum load that we will still respond to gitweb queries. + If server load exceed this value then return "503 Service Unavailable" error. + Server load is taken to be 0 if gitweb cannot determine its value. Set it to + undefined value to turn it off. The default is 300. Projects list file format diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl index 7e477af..3222131 100755 --- a/gitweb/gitweb.perl +++ b/gitweb/gitweb.perl @@ -221,6 +221,12 @@ our %avatar_size = ( 'double' => 32 ); +# Used to set the maximum load that we will still respond to gitweb queries. +# If server load exceed this value then return "503 server busy" error. +# If gitweb cannot determined server load, it is taken to be 0. +# Leave it undefined (or set to 'undef') to turn off load checking. +our $maxload = 300; + # You define site-wide feature defaults here; override them with # $GITWEB_CONFIG as necessary. our %feature = ( @@ -551,6 +557,26 @@ if (-e $GITWEB_CONFIG) { do $GITWEB_CONFIG_SYSTEM if -e $GITWEB_CONFIG_SYSTEM; } +# Get loadavg of system, to compare against $maxload. +# Currently it requires '/proc/loadavg' present to get loadavg; +# if it is not present it returns 0, which means no load checking. +sub get_loadavg { + open my $fd, '<', '/proc/loadavg' + or return 0; + my @load = split(/\s+/, scalar <$fd>); + close $fd; + + # The first three columns measure CPU and IO utilization of the last one, + # five, and 10 minute periods. The fourth column shows the number of + # currently running processes and the total number of processes in the m/n + # format. The last column displays the last process ID used. + return $load[0] || 0; +} + +if (defined $maxload && get_loadavg() > $maxload) { + die_error(503, "The load average on the server is too high"); +} + # version of the core git binary our $git_version = qx("$GIT" --version) =~ m/git version (.*)$/ ? $1 : "unknown"; $number_of_git_cmds++; @@ -3354,14 +3380,19 @@ sub git_footer_html { # 500: The server isn't configured properly, or # an internal error occurred (e.g. failed assertions caused by bugs), or # an unknown error occurred (e.g. the git binary died unexpectedly). +# 503: The server is currently unavailable (because it is overloaded, +# or down for maintenance). Generally, this is a temporary state. sub die_error { my $status = shift || 500; my $error = shift || "Internal server error"; - my %http_responses = (400 => '400 Bad Request', - 403 => '403 Forbidden', - 404 => '404 Not Found', - 500 => '500 Internal Server Error'); + my %http_responses = ( + 400 => '400 Bad Request', + 403 => '403 Forbidden', + 404 => '404 Not Found', + 500 => '500 Internal Server Error', + 503 => '503 Service Unavailable', + ); git_header_html($http_responses{$status}); print <<EOF; <div class="page_body">
-- 1.6.5.3