Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:112487
MIME-Version: 1.0
Date: Fri, 11 Dec 2020 10:59:01 +0100
Message-ID: <CAH5C8xVuRnsfO+_L+_zFD2uP9dJ3UNBNndCMcQPTnPmybtB8-g@mail.gmail.com>
To: PHP Internals List <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000270b6e05b62d587a"
Subject: [RFC] Measuring maximum execution time based on wall-time
From: kocsismate90@gmail.com (=?UTF-8?B?TcOhdMOpIEtvY3Npcw==?=)

--000000000000270b6e05b62d587a
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Dear Internals,

Currently, our company is migrating away from HHVM to PHP, and we are
experiencing some performance regressions due to the fact that the
max_execution_time ini setting has different semantics in the two languages=
.

By default, HHVM measures wall-time, but the behaviour can be controlled by
an ini setting (
https://github.com/facebook/hhvm/commit/9a9b42e3610cdf242f16ddb8936ce34adfa=
0be9e)
if compatibility with PHP is important. On the other hand, PHP measures the
CPU time on most systems (with the most notable exception of Windows),
which means that neither sleep(), nor network/system calls are counted
towards the timeout. This is really a big pain for distributed systems with
high traffic, where proper timeout settings prevent cascading failures.
Even if all the external calls have their own timeout settings, the script
itself has no control over the real execution time (e.g. there can be
dozens/hundreds of such calls).

That's why I'd like to add support for measuring the execution timeout
based on the wall-time. There are a couple of ways to approach the problem
though:
- by measuring wall-time on all platforms
- by adding a new "max_execution_time_type" or so ini setting for
optionally changing the meaning of max_execution_time (this is what HHVM is
doing)
- by adding a new "max_execution_wall_time" ini setting for being able to
timeout based on both the real execution time and the CPU time.

My POC implementation at https://github.com/php/php-src/pull/6504 currently
uses the third solution, but I would be okay with the other possibilities
as well (especially with the first one). I would also be very curious if
anyone is aware of the reasons why the CPU time metric was chosen back
then? In my opinion, wall-time is much more useful, but maybe I'm just
missing some technical limitations (?).

Please note that wall-time timeouts would take into effect on a best effort
basis, only after the network/system call exceeding the time limit is
finished.

Regards,
M=C3=A1t=C3=A9

--000000000000270b6e05b62d587a--