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Date: Tue, 3 Dec 2013 10:29:49 +0200
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To: Hannes Magnusson <hannes.magnusson@gmail.com>, Andi Gutmans <andi@zend.com>
Cc: Gustavo Lopes <glopes@nebm.ist.utl.pt>, Laruence <laruence@php.net>, 
	Dmitry Stogov <dmitry@zend.com>, PHP Internals <internals@lists.php.net>, Gadi Goldbarg <gadi@zend.com>
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Subject: RE: [PHP-DEV] strtr() performance degradation
From: zeev@zend.com (Zeev Suraski)

> -----Original Message-----
> From: Hannes Magnusson [mailto:hannes.magnusson@gmail.com]
> Sent: Tuesday, December 03, 2013 9:34 AM
> To: Andi Gutmans
> Cc: Gustavo Lopes; Laruence; Dmitry Stogov; PHP Internals; Zeev Suraski;
> Gadi Goldbarg
> Subject: Re: [PHP-DEV] strtr() performance degradation
>
> On Mon, Dec 2, 2013 at 10:54 PM, Andi Gutmans <andi@zend.com> wrote:
> >
> > On Dec 2, 2013, at 3:02 PM, Gustavo Lopes <glopes@nebm.ist.utl.pt>
> wrote:
> >>> =E2=89=88
> >>
> >> The progress consists of writing of scripts to test the point where to
> >> switch
> algorithms and trying some improvements on the old one without as
> expensive preprocessing steps.
> >>
> >> Now, this was in the summer... I'll have some time in the holidays to
> >> pick
> up this and some other PHP-related backlog; that said, if there's some
> impatience (which would be perfectly understandable...), I wouldn't mind
> if
> someone reverted to the previous state in the meantime.
> >
> > Sounds like this may take some time to figure out. So if there is
> > absolutely
> no difference in semantics between the two I would suggest we revert unti=
l
> you are able to dig into this.
> >
>
>
> This change was included in 5.4.12 and 5.4.22 has been released.
> Now you want to revert and maybe release 5.4.23 and then apply again in
> 5.4.24?
>
> That doesn't seem worth it. What done is done. Had it been reverted right
> away then it would have make sense, but not 10 releases later?

Hannes,

To put things in perspective, the work that goes into improving PHP's
performance by 10% is measured in months, sometimes more (from inception to
production).  Here, we have a patch that slowed real world apps (not
synthetic benchmarks) by over 10%, and despite the fact it was reported 6
months ago, we've done absolutely nothing about it.  If anything in that
story doesn't make sense, that would be it.

As to when we reintroduce it - I think it's absolutely fine that we don't
reintroduce it in the 5.4.x series, or even the 5.5.x series, but slate it
to 5.6.0 - and that too only if it's fully-baked by the time 5.6.0 is ready=
.
We've all experienced first-hand what a complete rewrite of a very popular
piece of code can do, and the fact that compatibility can be broken not jus=
t
by changing behavior, but also by radically changing the algorithm in a way
that produces very negative performance side effects.  Performance should b=
e
one of the measures by which we weigh compatibility - a major regression in
performance shouldn't be acceptable any more than a major regression in
functionality.

We should revert this patch ASAP;  It's unfortunate we haven't done it back
when it was found but better late than never.

Zeev