Excimer¶
Excimer is a low-overhead sampling profiler for PHP, developed by the Wikimedia Foundation. Unlike deterministic profilers such as Xdebug, which instrument every function call, Excimer periodically samples the call stack at a fixed interval, using a timer signal, which keeps overhead low enough to run in production.
Excimer can sample on wall-clock time or CPU time, which makes it useful for diagnosing both I/O-bound slowness, such as waiting on a database or a remote API, and CPU-bound slowness, such as heavy computation. Samples are collected into a log that can be aggregated into a flame graph or exported for further analysis.
Because sampling is cheap, Excimer is commonly left enabled at low sampling rates in production to catch real-world performance regressions that only appear under production load and traffic patterns, which synthetic benchmarks miss.
<?php
// Sample the call stack every 100ms of wall-clock time.
$profiler = new ExcimerProfiler();
$profiler->setPeriod(0.1);
$profiler->setEventType(EXCIMER_REAL);
$profiler->start();
// ... application code runs here ...
$profiler->stop();
$log = $profiler->getLog();
foreach ($log as $event) {
foreach ($event->getTrace() as $frame) {
echo $frame['function'] . PHP_EOL;
}
}
?>
See also Excimer on MediaWiki.org and Excimer on Packagist.
Related : Profiling, Blackfire, Tideways, Xdebug, Flame Graph, Performance
