Re: PHP 5.5 and APC user cache upgrade path

From: Date: Sat, 11 May 2013 10:10:10 +0000
Subject: Re: PHP 5.5 and APC user cache upgrade path
References: 1 2  Groups: php.internals 
Request: Send a blank email to [email protected] to get a copy of this message 
On 05/10/2013 08:54 PM, Christopher Jones wrote:



On 05/09/2013 05:02 AM, Pierre Schmitz wrote:

Hi,

I am testing PHP 5.5 atm and how we can package it for Arch Linux and
provide an upgrade path for users. The RC1 looks pretty solid so far.

As the new opcache does not provide a user cache to store custom
variables, I would be glad if you could clarify what the best migration
from 5.4 would be.
* Is APC basically dead and wont support PHP 5.5?


 From the lack of APC activity and from comments Rasmus has made in the
bugs (e.g. [1]) this is a safe assumption.


* Should APC users switch to opcache and APCu? (with APCu replacing the
APC package)


OPcache is definitely the opcode cache solution for PHP 5.5

For user data caches, there are a number of alternatives, as you
noted.  During this initial transition phase it isn't clear what the
directions of each solution will be.  It isn't clear that there will
be one dominant solution.  I'll leave it to Laruence and Joe to
state their cases for world domination of YAC and APCu, respectively.

Chris

[1] https://bugs.php.net/bug.php?id=64625



For PHP application developers:
* Regarding APCu: it provides the old PHP interface function as well as
their own apcu_* functions. They are aliases right now. Should
application developers think about switching to the apcu_-API as new
features will be available only here?

Bonus question:
* Right now very similar functionality is provided by APCu, XCache,
WinCache, YAC etc.. Are there plans to include such functionality inside
PHP in future to make application developers life a little easier? At
least a common API would be great. There were several bugs in
applications as these modules behave a little different regarding return
values etc..

Greetings,

Pierre





I am still waiting to see articles/blogs and the consensus on YAC.

YAC has a much higher throughput, if you are able to write the software to manage it and have the hardware to put up with it, then you should attempt to take advantage.

I'm not really sure if most have either the ability or the hardware; or if it's good thing to aspire to having either. Think about what is the advantage of using a cache, why does it create a more stable experience even when we do have the hardware to SELECT or request everything we need from wherever it comes ... it's because you are benefiting from the fact that the cache doesn't just make PHP faster because the opcodes Zend executes are less than fetching an un-cached result, but also, and mostly because it takes the pressure of MySQL, or your network connection, or your IO scheduler, or all of the above if you are clever about it. The problem with having no locking comes on a loaded server when many clients are attempting to read from an expired entry (this is the point where a cache has the effect of a stable service even under load where items have short ttls) the cache so they can avoid some significant work. In that situation, APC (and most others I assume) has a lock acquired by the first writer that cannot be obtained by a reader while it is held, the writer finishes (populating cache) the reader acquires the lock and is able to read that cached item, as are other readers. Good, only one context done what the cache is there to avoid. With YAC, or any solution that does not employ entry level locking, many contexts will end up doing the work, because a reader cannot see what isn't finished writing and will not implicitly wait for a write to complete.

Something to think about ...

Joe

Thread (10 messages)

« previous php.internals (#67397) next »