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Date: Tue, 14 Dec 2010 13:06:01 -0500
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To: PHP Internals <internals@lists.php.net>
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Subject: PHP Performance in Apache: Multi-Process vs Multi-Threaded
From: israelekpo@gmail.com (Israel Ekpo)

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Hi All,

I have a few questions about the performance of PHP web applications *under
load* and I would appreciate if there is anyone that would like to share
their experiences in terms of any benchmarks or observations.

*Background Information*

In multi-process environments, such as FastCGI, Apache Prefork MPM etc, PHP
needs to execute the MINIT and MSHUTDOWN functions for all loaded extension=
s
on every request.

In a multi-threaded environment, such as Apache Worker MPM, with Zend Threa=
d
Safety is enabled,
PHP only needs to execute MINIT and MSHUTDOWN functions once for each
extension and not each time a new thread is created to serve a request.

It is also more expensive to create new processes than to create new
threads.

In one-on-one comparisons between scripts executed only once in ZTS mode an=
d
scripts executed once in non-ZTS mode,
I noticed that the one in non-ZTS mode was slightly faster and this seems t=
o
be the main reason why most people go with the non-ZTS enabled setups.
But the reason for this slight difference in speed is because of the
differences in the data structure for globals for ZTS and non-ZTS modes.

Other reasons people have cited for going with non-threaded setups include
stability which I guess we should not really be concerned about if
non-threadsafe extensions are excluded.

Since it is generally more expensive to create new processes than new
threads, I believe that under high load, php in ZTS mode (multi-threaded
environment) will perform better than an identical setup in NTS mode
(multi-process).

*Problem*

I noticed that Zend Server is using PHP in FastCGI mode (multi-process NTS)
and I am contemplating setting up apache in worker mode (threaded mode) and
compiling php in ZTS mode instead.

Has anyone performed any load tests benchmarks comparing the two setups
(Multi-Process vs Multi-Threaded)?

Are there PHP extensions that cause issues in threaded environments that I
should avoid?

Are there any internals information or any other reasons why I should choos=
e
ZTS over NTS or vice versa?

Any useful feedback will be highly appreciated.

Thanks.

--=20
=C2=B0O=C2=B0
"Good Enough" is not good enough.
To give anything less than your best is to sacrifice the gift.
Quality First. Measure Twice. Cut Once.
http://www.israelekpo.com/

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