Support » Networking WordPress » Should WordPress MultiSite operate OK with 512MB of RAM?

  • Resolved gtch


    I am currently setting up a WordPress Multisite installation with just two sites. WordPress isn’t coping, with admin pages being extremely slow (10+ seconds per page).

    A major culprit seems to be RAM: total RAM usage hovers around 800MB, but I’m actually running on a 512MB RAM virtual server. I don’t know how the virtual server overallocates RAM by 50%, I suspect that ‘extra’ RAM is on disk hence WordPress slowing to a crawl.

    My question is: should WordPress MultiSite be able to run OK in on a server with 512MB RAM?

    If so, then obviously the next question is what could be wrong with my configuration? I’d love to hear suggestions on what to investigate. My configuration is:

    • Virtual server with 512MB RAM – a MediaTemple (ve) server
    • Running Ubunto 10.04 LTS
    • Webserver is Apache 2.2.14
    • PHP version is 5.3.2-1ubuntu4.9
    • PHP memory_limit is 96MB
    • MySQL version is 5.1.41-3ubuntu12.10
    • WordPress version is 3.1.3
    • Enabled WordPress plugins are ‘WordPress Importer’, ‘Jetpack’ and ‘WP Super Cache’
    • Upon startup of Apache/WordPress, total server memory usage is around 200MB
    • Within a few minutes of use it climbs to 700-800MB


Viewing 5 replies - 1 through 5 (of 5 total)
  • Moderator Ipstenu (Mika Epstein)


    Lead Plugin Wrangler

    Yes, it should run fine, depending on how many sub sites you have.

    I would start by optimizing the server for wordPress. You may need to change some min/max settings and apply server side caching like APC or memcahce.

    I have a multisite (directory) site []with 7 Directories and many other subsection with other programs which run on 345MB VPS server, with 372000 unique visitor last month.
    it uses only 43% of 345MB after tweek.

    see more in details here [ ]

    you can use lighttpd instead apache it will reduce half of the load too, if your supports.

    Thanks for the links. I plunged into a number of sites and after a few hours have emerged having determined that the primary problem is Apache HTTPD’s default preforking settings.

    I’ve fixed up my memory problems. Admin is faster but still unacceptably slow; I think I’ll have to move on to MySQL optimisation next to fix that up. The good news is that blog pages are lightening fast now!

    Here is some help for anyone else having problems with overrunning memory with WordPress…

    How to fix up preforking on Apache HTTPD

    In a Linux environment Apache HTTPD will prefork (ie create) up to 150 threads in advance to handle requests. Each of those threads appears to have a complete instance of WordPress code running in it; on my machine that requires around 40-45MB. That means 40-45MB of private memory per thread. Within a few minutes of startup Apache would have around fifteen threads running, and 15 ✕ 45MB = 675MB which is more RAM that I actually had.

    However those threads are completely unnecessary on my small site. They’re sitting there waiting for requests and over 99% of time they’ve got nothing to do. So I drastically reduced the limits, allowing only 10 threads to be preforked instead of 150.

    My Apache HTTPD configuration now contains:

    <IfModule mpm_prefork_module>
        StartServers          2
        MinSpareServers       2
        MaxSpareServers       6
        ServerLimit		  10
        MaxClients		  10
        MaxRequestsPerChild   1000

    This has fixed my problem, dropping my peak memory usage to below 512MB.

    How to keep those threads healthy

    One problem with dropping the number of threads is that it limits my server to handling only 10 requests at once. But my site is small and I doubt that I’d hit this limit soon; and Apache queues up requests so spikes should be smoothed out.

    Even so, better safe than sorry. A few things I picked up in my reading are:

    • Use a webserver-level cache like WP Super Cache
    • Reduce Apache’s request timeout
    • Reduce Apache’s Keep-Alive timeout

    Using WP Super Cache with the ‘Use mod_rewrite to serve cache files‘ setting enabled means that Apache HTTPD serves up the pages directly. This means each thread completes its work very quickly, and thus will be ready for the next request more quickly.

    Reducing the request and Keep-Alive timeouts in Apache HTTPD configuration is very important. By default the request timeout is five minutes, so if the browser doesn’t acknowledge the response then that thread would not be available for the five minutes. Ten requests like that and your website disappears for a few minutes! I’ve dropped mine to 45 seconds.

    The default Keep-Alive timeout is 15 seconds. This means that when Apache finishes handling a request from a browser that use Keep-Alive (which is most browsers) it waits 15 seconds for further requests before allowing someone else to use the thread. This could limit a thread to serving up only four pages a minute; reducing the KeepAliveTimeout setting to 3 seconds means a thread could handle more like twenty pages a minute.

    Useful references

    These two posts really helped me:

    Optimize Apache for WordPress

    Andrea Rennick


    Customer Care at Copyblogger Media and Studiopress

    Media Temple actually has an article in its knowledgebase about tweaking this.

    Seems like a consistent issue on their servers, tho I have used the same tweak on others.

    Ahh yes, so they do. However the numbers on that Media Template page are a bit too high for WordPress MultiSite… simpler web applications would be fine with those numbers, but WordPress MultiSite seems to require a lot more memory per thread.

    For my particular configuration, ten threads seems to be working well.

Viewing 5 replies - 1 through 5 (of 5 total)
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