We have noticed that our application occasionally times out. When this happens, logs nearly always indicate that the script stopped execution at "promphp/prometheus_client_php/src/Prometheus/Storage/APC.php on line 72" (sometimes line 71).
This is the following block inside \Prometheus\Storage\APC::updateHistogram
// Atomically increment the sum
// Taken from https://github.com/prometheus/client_golang/blob/66058aac3a83021948e5fb12f1f408ff556b9037/prometheus/value.go#L91
$done = false;
while (!$done) {
$old = apcu_fetch($sumKey);
if ($old !== false) {
$done = apcu_cas($sumKey, $old, $this->toBinaryRepresentationAsInteger($this->fromBinaryRepresentationAsInteger($old) + $data['value']));
}
}
My very superficial understanding leads me to believe that apcu_cas may be unlikely to return true if another process (or many processes) are also continuously updating the value stored at $sumKey, since $old may no longer match the persisted value.
Do you see any cause for concern or is my analysis incorrect?
We have noticed that our application occasionally times out. When this happens, logs nearly always indicate that the script stopped execution at "promphp/prometheus_client_php/src/Prometheus/Storage/APC.php on line 72" (sometimes line 71).
This is the following block inside \Prometheus\Storage\APC::updateHistogram
My very superficial understanding leads me to believe that
apcu_casmay be unlikely to return true if another process (or many processes) are also continuously updating the value stored at$sumKey, since$oldmay no longer match the persisted value.Do you see any cause for concern or is my analysis incorrect?