I am running PHP Version 5.3.5 and developing a website in Codeigniter 2.1.3
I am working now to improve website performance, and I found caching can be used like APC or memcached or Zend OpCache.
In codeigniter I used $this->output->cache(43829); for caching.
Output of actions got cached, and It returns same output on every request.
But I have dynamic pages so this caching will not work. I am looking around how APC can be used for ope-code caching and used to enhance web site performance.
Is APC stores opecode in cache that cane be used by zend engine for execution execution, without regenerating opecode on each request?
Attached is my PHP APC configuration
PHP 5.3 is nearly 2 years past end of life, and APC is not available for current PHP versions. PHP 5.5+ comes with Zend Opcache, which has equivalent functionality. Instead of trying to get your site to work with old technologies, simply upgrading your server to a current (and secure) version of PHP would give you this performance boost without you having to do anything else.
Output of actions got cached, and It returns same output on every request
While its faster than regenerating the page, its still far from optimal. Better to use a caching reverse proxy in such a case.
I am looking around how APC can be used for op[e]-code caching
Your question implies that you think you are not already using op-code caching. I suggest your first port of call is to see if it is already enabled. You can see this from the output of phpinfo() or check function_exists('apc_sma_info');
APC is unlikely to be provisioned for future versions of PHP. ZOP+ is the opcode cache which is currently bundled with PHP 5.4+. It will work with 5.3, but requires some effort. Tim is correct in saying the 5.3 is past its sell-by-date and should be upgraded.
Note that ZOP+ also includes an optimizer (and, rather alarmingly, it seems to have a significant impact on the performance of many frameworks). The performance of ZOP+ is more dependent on sizing the cache than in APC - but even with APC, sizing the cache wrongly will not give good results.
Related
I'm just wondering is it stupid to use both Xcache 3 with Zend Opcache at the same time to cache PHP files? I know that both do almost the same job, but not sure if that would make any difference on the performance and speed.
I want to speed up my php page load so that visitors don't need to wait long.
any thoughts on that?
To answer your question: Yes, you should not run xcache and Zend Opcache at the same time. If you do, you'll get undefined behaviours, most notably "cannot redeclare class XYZ" fatal errors. That happened to me after a systems upgrade, where the packet maintainer activated Zend Opcache along the already existing xcache installation.
As for the matter of which of both to use for opcaching, that depends on your specific code - I'd recommend setting up a test environment and firing up the Apache Benchmark or a similar tool to check the answer times.
On a default wordpress installation, I was able to get a speedup (uncached vs xcache) of about 5-7x, which is quite significant. If you really need more, you'll need to check out the other possibilities already mentioned in the comments like
using a loadbalancer and multiple application servers
using memcache or memcached to cache database queries and other load heavy operations
switching to another database system like a NoSQL system (be careful of the consequences)
changing your architecture to a static site with webservices providing interactive content
I've searched all over the web for documentation including on the XCache website.
I'm new to PHP opcode caching and XCache. I'd like an explanation of how XCache works. I know that it stores compiled php code so that it doesn't need to be recompiled everytime. But how does XCache know when php code has been updated and thus the cache is out of date?
How do I know if I need to clear the cache?
Does XCache compile and cache all php code on the server? If so can this be configured?
What are clogs? OOMs? I see large numbers for both of these in the XCache Admin page interface.
In the Code Coverage Viewer... what does Percent mean? Is this the percentage of code that has been cached?
Does hits mean the number of lines of compiled code that has been read from cache?
Does lines mean the total number of lines of code?
What is the ToDo column for?
Why are some lines highlighted in red?
I'm using PHP 5.3.2, XCache 1.3.0, and Ubuntu 10.04 if it helps.
Xcache:
optimizes performance by removing the compilation time of PHP scripts
by caching the compiled state of PHP scripts into the shm (RAM) and
uses the compiled version straight from the RAM.
Based on observations using PHP 5.5.3 and Xcache 3.1.0 this is what I can deduce:
Cacher
This module deals with two kinds of caching Opcode and Variable.
The Opcode caching is designed to be a simple drop-in. You can't customize how it decides to cache, just how much:
xcache.count setting refers to how many cache threads and correlates to how many processor cores you want to utilize — the idea is that multithreading should be the fastest, but there is no guarantee so experiment yourself
As a guideline, valid count values would be 2^n like 1, 2, 4, 8 — 0 will disable the cacher and other values will get rounded to the nearest valid value
xcache.size setting refers to the aggregate memory of all cache threads. So, each thread gets roughly size/count amount of memory
OOM aka Out of Memory, refers to the event of a cache thread hitting it's maximum size
Variable caching requires using a simple get/set api in your app code. After enabling it using xcache.var_size and xcache.var_count (similar to Opcode settings) you use xcache_set($var1) and xcache_get($var1) in your scripts.
Invalidation
The xcache.stat setting controls whether or not to check if the file was modified since it was cached:
When set to On files get checked and re-cached
When set to Off skips the check will keep the first cached version as long as the expiration time, which could help performance by limiting disk i/o
In your dev environment it's a good idea to keep it On so you can update and check your code continuously — otherwise you have to flush the cache to see updates to files.
Flushing
There is a web admin interface which allows you to flush a particular cache. The web admin uses a php api: xcache_clear_cache(…).
Since the cache is RAM based anytime the server restarts the cache should be flushed.
Expiration
Cached items expire according to xcache.ttl and xcache.var_ttl which respectively control the number of seconds a cached item lives (0 is indefinite and the default).
Coverager
The coverager module, aka Code Coverage, is a little mysterious. According to the FeatureList it seems like a diagnostic tool intended to be enabled for temporary administrative/testing situations:
Coverager + real life testcase framework, this include: [TOSHARE]
real life testcase framework, a control script with real browser. you have to write the test cases.
builtin Coverager + its viewer from web, to see how much script you have tested.
the testcase+Coverager just help you make sure all real life php web applications is running correctly when
after enabling XCache
after upgrading php4 to php5
after upgrading php4/5 to php6
A friend has recommended that I install php APC, claiming it will help php run faster and use less memory
sounds promising but I'm a little nervous about adding it to my VPS server
I have one small app that I've built using codeigniter, and several sites that use the popular slideshowpro photo gallery software
could install this break any of the back end code on my sites?
I'm no high tech server guy, but should I give this a try?
Depends entirely on your situation.
Is your site unresponsive or slow at the moment? Is this definitely due to the PHP scripts and not any other data sources such as a database or remote API?
If you answered yes to the above, then installing one of the many PHP accelerators out there would be a good shout. As for using less memory, that's largely dependent on your apache/lightppd/nginx config and php.ini variables.
Most PHP accelerators work by converting the (to be) interpreted PHP code into opcode. This is then stored in memory (RAM) for fast access. If you haven't already implemented file-based caching in CodeIgniter then the benefits of installing a PHP accelerator would be noticeable. If you haven't, then I suggest you do that first before moving straight over to (wasting?) spending time trying to install APC manually.
If your site is currently performing well and you're not too confident in your *nix skills then I suggest you try implementing CodeIgniter caching first rather than try messing with what is an already working VPS.
My personal preference is PHP eAccelerator.
Should installing a PHP cache engine not improve your site's performance then I suggest you look at what other factors influence your application. As stated above, these could be: database or API to name a few.
Hope this helps.
APC is basically a cache engine that stores your compiled php scripts on a temp location on your server. Meaning that these do not have to be interpreted every time someone calls your sccript. It is a PHP extension can can safely be turned ON or OFF and it does not affect your actual code. So... do not fear!
When a php script is processed, there is a compilation phase, where php converts the source code of the php files into "opcodes". APC simply caches the result of this compilation phase, so it should be safe to turn on.
That said, when making such changes to production code it is always wise to run a regression test to ensure no new issues have been introduced.
I have started having problems with my VPS in the way that it would faill to serve the pages on all the websites. It just showed a blank page, or offered to download the php file ( luckily the code was not in the download file :) ).
The server was still running, but this seemed to be a problem with PHP, since i could login into WHM.
If i did a apache restart, the sites would work again.
After some talks with the server support they told me this is a problem with the APC extension witch they considered to be old and not recommended for production servers. So they removed it for now, to see if the same kind of fails would continue to appear.
I haven't read anywhere that APC could have some problems or that its not always recommended to use, quite the contrary ... everywhere people are saying to always use it.
The APC extension was installed ssh and is the latest version.
Edit:
They also dont recomend MemCache and say that a more reliable extension would be eAccelerator
Um APC is current tech and almost a must for any performant PHP site.
Not only that but it will ship as standard in PHP 6 (rather than being an optional module like it is now).
I don't know what your issue is/was but it's not APC being outdated or old tech.
I run several servers myself and the only time I have ever had trouble with APC was when trying to run it concurrently with Zend Optimizer. They don't work together so if I must use Optimizer (like if some commercial, third-party code requires it) I run eAccelerator instead of APC. Effectively 6 of one, half-dozen of another when it comes to performance but I really doubt APC is the problem here.
Just to add, memcached is only going to benefit you greatly if you are running multiple servers which need to access a shared data cache. Memcached does not do opcode caching like APC/eAccelerator/Xcache/etc.
The problem is not to do with APC. If APC had a problem, it would either show up in your php log file or you simply wouldn't be able to access your website until you adjusted APC. The problem is more likely with apache itself. I've experience the same problem as you with blank pages before and it was to do with mod_security playing up and preventing pages from being sent that looked "suspicious". Also, memory usage in apache is good at killing the server under load. I've also had experience with a web host that had compiled apache with a memory leak so every X amount of requests (say 100,000) the server would crash! Most annoying.
Your web host doesn't sound the most competent out there as they are giving some bad advice, most likely based on ignorance.
APC should be used on production (with the mstat check turned off on production, but on for development). You can get more stats about your apc setup while it's working by loading the apc status file that comes with it and you get a nice page like this: http://drupal.org/files/images/APC%20Status-1.png
Memcache is very heavily used as it's also distributed! The use for such is as follows:
APC is the fastest as it works most closely to php, but only works on the same server executing the PHP itself so it's use is limited in that scope. Used primarily as an opcode cache.
Memcache is like a very fast database spread over many computers working as one unit. However, a powercut will wipe the lot!!! Hence why they are heavily used to remove preasure from the persistant database. Facebook and many other sites have hundreds of servers running memcache.
My advice would be to find a web host that understands PHP. Fighting web hosts is hard work about whos right and whos wrong... until you find a good one ;)
Sounds to me like they are pushing a product that they probably have referral kickbacks on.
I run my own servers (have for a while) and I've never had this problem, not any MAJOR problems with MemCache.
Does anybody have experience working with PHP accelerators such as MMCache or Zend Accelerator? I'd like to know if using either of these makes PHP comparable to faster web-technologies. Also, are there trade offs for using these?
Note that Zend Optimizer and MMCache (or similar applications) are totally different things. While Zend Optimizer tries to optimize the program opcode MMCache will cache the scripts in memory and reuse the precompiled code.
I did some benchmarks some time ago and you can find the results in my blog (in German though). The basic results:
Zend Optimizer alone didn't help at all. Actually my scripts were slower than without optimizer.
When it comes to caches:
* fastest: eAccelerator
* XCache
* APC
And: You DO want to install a opcode cache!
For example:
alt text http://blogs.interdose.com/dominik/wp-content/uploads/2008/04/opcode_wordpress.png
This is the duration it took to call the wordpress homepage 10.000 times.
Edit: BTW, eAccelerator contains an optimizer itself.
MMCache has been deprecated. I recommend either http://pecl.php.net/package/APC or http://xcache.lighttpd.net/, both of which also give you variable storage (like Memcache).
Both are interesting and will provide speed boost since they compile source code into binary representation which is then executed by the PHP engine.
Any huge web site running with PHP (Facebook for example) is running some sort of opcode cache system like MMCache.
The problem is that they are not very easy to set up depending on your system.
Depending on how much of your PHP code is actually executed and how long that execution takes they can be a really big win. It certainly isn't going to hurt, but the gain you see will very much depend on where your time is currently spent.
btw mmcache has been rolled into a different project now, I forget the name but Google will tell you.
I use APC on my production servers and it works pretty well out of the box. Compile it and add it to PHP and there isn't much tweaking left to do for it. I check it every once in a while just to review stats but since I use MVC a lot all of the main files (routers, controllers, etc) rarely change on a day-to-day basis so that code stays compiled and runs pretty efficiently.
currently we use apc, free and was just a simple plug and play on our live servers. Provided a huge performance increase for our site, especially as the project size increased. I also have the apc.stat disabled so it doesn't check if the code has been updated, so whenever we need to update the code on the live site we restart apache.
I use APC, and can attest that it can dramatically reduce the CPU and I/O load on an app server if you maintain a high cache-hit rate. It not only saves you from having to compile, it can save you from having to read the php files from disk at all. (i.e. the bytecodes are served directly from main memory, so it's super fast) It lowers the speed to render a single page, and increases the requests per second your server can handle.
If you use RedHat or CentOS, installing APC is super simple:
yum install php-devel httpd-devel php-pear
pecl install apc
echo "extension=apc.so" > /etc/php.d/apc.ini
# if you're using SELinux:
chcon "system_u:object_r:textrel_shlib_t" /usr/lib/php/modules/apc.so
/etc/init.d/httpd restart
You asked about downsides. The only downside is that it requires some memory. The default on APC is 30MB, but it can be adjusted, and the cost of a little bit of memory more than pays for itself with the increased speed and response rate.
BlaM's testing included all the DB calls made by WordPress. When you're making fewer DB calls, you'll see the performance gain of opcode caches be even more dramatic.
I used Zend Accelerator a little back in the day (2004-ish). It certainly gave some significant performance wins on code it could work with, but unfortunately the system I was using was designed to quite often dynamically load code and then eval it, which Zend Accelerator couldn't do much with at the time (and I'd guess still can't).
On the down side, we certainly saw some caching issues (where the code would be changes, but the compiled version sync with the change for one reason or another). I imagine those problems have likely been ironed out by now.
Anyway, I don't have any hard comparison numbers, and certainly didn't write the same system in different environments for comparison, but for the vast majority of systems, PHP isn't going to kill you performance wise.
Have you checked out Phalanger? It compiles PHP to .NET code. Here are some benchmarks which show that it can dramatically improve performance.