A set of scripts for getting useful performance data out of HHVM's Xenon extension.
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Arc Lamp

Arc Lamp comprises a set of scripts for getting useful performance data out of HHVM's Xenon extension. The Xenon extension captures a trace of PHP code at regular intervals. When aggregated, the data generated by the Xenon extension call help you determine where your program is spending the most time.


Quick start

First, enable the Xenon extension in HHVM's INI file by setting hhvm.xenon.period. This setting specifies the interval (in seconds) between trace captures on each host. If your PHP application is served by just one server, you can set this value to 60 to make Xenon capture a trace once a minute. If you have more than one server, you can use the following formula to help you choose a value:

hhvm.xenon.period =  60 * servers / desired_number_of_samples_per_minute

So, for example, if you want to log a trace every 30 seconds, and you have 10 PHP application servers, the value is 60 * 10 / 0.5 = 300.

require_once 'ArcLamp.php';

register_shutdown_function( 'ArcLamp\logXenonData', array( '', 6379 ) );


Copyright 2014 Ori Livneh ori@wikimedia.org

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at


Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.