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Date: Sat, 24 Nov 2018 01:49:50 +0200
Message-ID: <CAJHtznxOm=YR8FcUDx_M-Fv9WgP-PtT+vg4G5_sMom2EJK5iEA@mail.gmail.com>
To: rowan.collins@gmail.com, Dmitry Stogov <dmitry@zend.com>
Cc: Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [mini-RFC] Disable opcache per script using "declare(cache=0)"
From: zeev@php.net (Zeev Suraski)

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On Sat, Nov 24, 2018 at 1:18 AM Rowan Collins <rowan.collins@gmail.com>
wrote:

> On 23 November 2018 12:48:40 GMT+00:00, Dmitry Stogov <dmitry@zend.com>
> wrote:
> >Especially, the main preload.php, usually should be marked, to disable
> >its caching.
>
> Sorry, could you explain for those of us in the peanut gallery why this is
> the case? I'm struggling to understand what it means to preload something
> but not cache it, and suspect I'm missing something fundamental.
>
>
I'm not sure if you're missing anything fundamental - it's just that the
preload.php file Dmitry's referring to (the one that's responsible to
loading all the other files) - is one file that's pretty much by
definition, will be of no use at any later point in the lifetime of the
server.  It preloads other files (which of course, should very much persist
in the opcache memory) - but once it's done, it's done.  That's why it kind
of makes sense not to cache it.

That said, I'm not sure whether having this feature as a declare() makes
sense - at least in the context of the new preload feature.  The preload
file is likely to be fairly small, wouldn't it consume negligible amounts
of shared memory and just one slot in the files table?  And like Pierre
suggested, perhaps we can simply default to not caching the main preload
file (i.e. the one referenced by php.ini).

Outside the context of preloading, there's probably some value in having
this new declare() option.  There are situations where you simply don't
want to cache certain files (what I usually bumped into was in case of
auto-generated, short-TTL files).  That's why a lifetime or two ago we
added the blacklist feature - the declare() syntax would offer a new way to
do that that is configurationless and built into the code.  In that sense,
it's not a bad thing.  I'm just seeing it as not so much related to
preloading, and more of a general-purpose feature.

Unless of course I'm missing something..?

Zeev

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