This is a known problem for anyone who runs Magento and uses memcache as a caching backend. But it’s actually not a Magento issue, it’s a Zend Framework problem, and it seems that even newer versions of ZF still have the same approach. I suspect this is actually a memcache problem, but even so, one should be able to handle things better in the code.

The idea is that memcached sometimes fails to report its extended stats, thus the “getExtendedStats” method returns false, when in fact it should return an array with all the servers. This should not be a problem though, instead of throwing an exception, why not retry with getStats and then just return 100 (which I guess it means the server is full). Here’s the revised code:

if ($memSize === null || $memUsed === null) {
    $mem = $this->_memcache->getstats();
    if (isset($mem['limit_maxbytes']) && $mem['limit_maxbytes'] > 0) {
        return ((int) (100 * ($mem['bytes'] / $mem['limit_maxbytes'])));
    } else {
        return 100;
    }
 
    //Zend_Cache::throwException('Can\'t get filling percentage');
}

You can get the entire file on github, but please note that this file corresponds to ZF v1.11.1 and Magento CE v1.5.1.0. It can definitely be adapted to any Magento version.

The easiest way to patch this without changing a core file (ie lib/Zend/Cache/Backend/Memcached.php) is to put the modified file in your app/code/local folder:
app/code/local/Zend/Cache/Backend/Memcached.php. since app/code/local comes first in the include path, the patched file will get included before the default one.

Disclaimer: This hasn’t been used in production, use at your own risk. In theory, it should be fine, but since it hasn’t passed any real testing, I don’t recommend doing so.

Cristi Magento Magento, memcached, patch

Memcached is a free open source, high-performance, distributed memory object caching system. It is currently used by a lot of websites, including Flickr, Twitter, Youtube, Digg and WordPress.

I’ve been using memcached on a few production servers, but never thought it could come in handy on a Windows development machine – in fact I didn’t even thought it was available on Windows. So, a few days ago, while working on yet another Magento project, I ran a Google search for “memcache windows” and it turned out there are a few Win32 ports of the original version. Cool! It can be used on Windows, now all I need is to find the right PHP extension.

Here’s a step-by-step tutorial on how to get memcached running in PHP on a Windows box. There’s are a bunch of really good tutorials out there, but I think another could only be helpful.

1. Go to http://splinedancer.com/memcached-win32/ and download memcached. I’ve used the 09.03.2008 binaries, memcached 1.2.4.
You can also use v1.2.6 that you can download from http://code.jellycan.com/memcached/ – I’ve used this one to update from the previous 1.2.4 and I can confirm that it works.

2. Unzip the downloaded file to any folder (i.e. C:/memcached). I’ve saved in the same place where I have Apache, MySQL and PHP.

3a. If you’re on Windows Vista, navigate to your memcached folder, right click on memcached.exe and click Properties, then click the Compatibility tab. In here, check the “Run this program as an administrator” checkbox.

3. Install the service by running memcached.exe -d install from the command line. (you should be in the folder where you unzipped the file(s), ie: c:/memcached)

By default, memcached has 64M available for caching and runs on port 11211. If you need to change any of these you can do it by editing the Registry – open regedit then search for HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/memcached Server. Change the ImagePath entry from "C:\memcached\memcached.exe" -d runservice to "C:\memcached\memcached.exe" -d runservice -m 256 -p 11222". This gives you 256 megs of memory and change the port to 11222 (on a development machine you probably don’t need to change the port, but who knows). See the full list of memcached options – not sure which ones apply to the Windows version too.

4. Now, that the service is installed and configured, let’s start it: memcached.exe -d start
To test that memcached is running you can try telnet’ing – telnet localhost 11211 (use the port you configured the service to listen to). If you can connect on that port, everything is fine.

5. Memcached is installed, but we need to use in PHP, so we need an extension. Here’s a list of sites where you can download the dll from:
http://downloads.php.net/pierre/
http://www.pureformsolutions.com/pureform.wordpress.com/2008/06/17/php_memcache.dll
http://kromann.info/download.php?strFolder=php5_1-Release_TS&strIndex=PHP5_1
shikii.net/blog/downloads/php_memcache-cvs-20090703-5.3-VC6-x86.zip

I had to install a VC6 dll, so I’ve downloaded the last one. Unzip it and put it in your php extensions folder. If you don’t know where this folder is, try this command: php -i | find "extension_dir". Add the dll in there, then open php.ini (to find it, you can run php -i | find "Loaded Config") and at the end add something like this:

[PHP_MEMCACHE]
extension=php_memcache.dll

Now restart Apache.

6. To test that memcached can now be used in PHP, use the following snippet:

$memcache = new Memcache;
if( !$memcache->connect('localhost', 11211)) { //change 11211 with the port your memcached is configured to listen to
  die('Could not connect!');
}

echo '
';
print_r($memcache->getStats());

If you see an array with a bunch of data in it, you’ve done it. If not, something went wrong at some point. Make sure memcached is running, then make sure you’ve got the correct php settings and extension.

As I mentioned at the beginning of the post, installing memcached was something that just hit me while working on a Magento project – for those familiar with Magento, you know how slow it can be sometimes, especially when you need to constantly refresh the pages to check html/js/css changes. So, I thought memcached would help speed up the parts on which I wasn’t working on – everything except layouts and html block cache. And so it did, development seems MUCH easier now – but all about this in another post, soon to come.

Many thanks for helping me figure this out and (hopefully) speeding up development to:
http://splinedancer.com/memcached-win32/
http://pureform.wordpress.com/2008/01/10/installing-memcache-on-windows-for-php/
http://shikii.net/blog/installing-memcached-for-php-5-3-on-windows-7/

Cristi PHP memcached, performance, PHP