Questions[memcache](server)

I'm a bit new to Memcache and Redis and I'm trying to understand the difference between the two and what each actually is.

As has been explained to me Memcache is a database caching solution. Data from frequently run queries are cached to be re-used at a later point speeding up response time. Is that an accurate description?

What about Redis? Does that work in a similar manner? In other words does it cache data it receives from a backend database? I keep reading that Redis is is a key value store solution which to me sounds like more of a replacement for a database server vs a db caching solution.

Any help understanding what each is and what the differences are would be greatly appreciated.

Thanks Brad

I want to set up Nginx as my web server. I want to have image files cached in the memory (RAM) rather than disk. I am serving a small page and want a few images always served from RAM. I don't wish to use Varnish (or any other such tools) for this as I believe Nginx has a capability to cache contents into RAM. I am not sure as to how I can configure Nginx for this? I did try a few combinations but they didn't work. Nginx uses disk all the time to get the images.

For example, when I tried Apache benchmark to test with following command:

ab -c 500 -n 1000 http://localhost/banner.jpg

I get the following error:

socket: Too many open files (24)

I guess this means Nginx is trying to open too many files simultaneously from the disk and OS is not allowing this operation. Can anyone please suggest me a correct configuration?

I've been asked to launch a site that someone else built. It is a Wordpress shop site that needs Memcached to run, and I've been having troubles getting Memcached and the memcache php plugin working on my local server. Before installing memcached and the memcache PHP plugin, I would get this error:

Fatal error: Class 'Memcache' not found in [Path]wp-content/object-cache.php on line 350

Now that I have memcached and the memcache PHP plugin installed (via Homebrew), I get a "No data received" page, and get this error in my Apache error log:

dyld: lazy symbol binding failed: Symbol not found: _mmc_queue_pop
  Referenced from: /usr/lib/php/extensions/no-debug-non-zts-20090626/memcache.so
  Expected in: flat namespace

dyld: Symbol not found: _mmc_queue_pop
  Referenced from: /usr/lib/php/extensions/no-debug-non-zts-20090626/memcache.so
  Expected in: flat namespace

[Sat May 05 16:38:27 2012] [notice] child pid 26491 exit signal Trace/BPT trap (5)

I've tried looking for that pid in Activity Monitor to no avail, and it changes every time I try to load the page. Also, I can't find anything about _mmc_queue_pop anywhere.

I'm running Mac OSX Lion, PHP ver 5.3.8, Memcached ver 1.4.13, and Memcache PHP plugin ver 3.0.6.

Does anyone know how I can fix this?

Thanks!

I have installed memcache for a Drupal site with the memcached pecl extension. It's all running fine but I'm still struggling with the configuration settings.

For instance , following advice on drupal.org

You should probably lock down the memcache server so that it only listens for 
connections from the hosts that need to be served, as the default is that 
memcache listens to connections from all addresses. 
So, to close that hole, edit /etc/sysconfig/memcached with:

OPTIONS="-l ${HOSTIP}"

Problem is that I don't have this file on my server, in any case not at this location. Some other articles have mentioned /etc/memcached.conf but I can't find this file either.

Considering that the /etc/sysconfig/memcached or /etc/memcached.conf do not exit on my server, can I safely create them? Is it possible for these files to be situated somewhere else, in which case where should I look or is there any way to find that info?

Finally , any resources, tutorials or documentation links would be greatly appreciated. I've browsed thru memcache's site Wiki, and could only find a couple of relevant articles for beginners.

I am currently on a Xeon 7550 server running Redhat x86_64 es5 with 32gb RAM. I have memcache installed and the only step remaining in the configuration is to set how much memory it uses. I had done this on my old server, where I downloaded a file on through Filezilla (root access) and edited it. Now, I cant remember which file I edited and exactly how the process went. I want to set the memery to use 1 GB.

Anyone with some insight? Please be thorough if you will assist, as my linux server knowledge is limited.