Memory

My #1 Trick to Drastically Reduce WordPress Memory Usage

I was working on a client’s new WordPress site when I got the dreaded Linux “out of memory” error in my browser unexpectedly:

Fatal error: Out of memory (allocated 63963136) (tried to allocate 7864320 bytes) in [path]/wp-content/plugins/wordfence/lib/wfBrowscapCache.php.php on line 16388

I had never gotten this before, so I Googled around. Almost everywhere I looked, the advice was to increase your PHP and WordPress memory limits, or add memory to your server, or to remove plugins.

I didn’t want to just increase my allowable memory though. I wanted to solve the root cause of the problem. The site was running on an Amazon EC2 small instance with Amazon AMI. It should not be running out of memory!

If you want to go directly to my results, jump ahead to my recommendations. Otherwise, here’s my story:

How I Investigated This Problem

I installed the TPC! Memory Usage Plugin on my live site. [Note: I no longer recommend that plugin since it’s not maintained. Use Server IP & Memory Usage Display instead.]

I installed this plugin on my local development site as well and was totally blown away when I compared the memory usage on my local site vs. live site:  the same site with the same plugins was using 34.13MB on my local server and 60.0MB on the live site. WOW!!!

How could this be? There must have been something in the server setup that caused the discrepancy. Googling some more, I read that PHP5.4 uses significantly less memory than PHP5.3, by a huge amount, on the order of cutting it in half. Sure enough, I checked and found out that my local server was running PHP5.4 while my live server was running PHP5.3. It seemed like a smoking gun, but I needed to do one more experiment to be sure.

I had another WordPress site running on Amazon EC2 with Amazon AMI, running PHP5.3. Memory usage for that was 47.8MB. After I upgraded that server to PHP5.4, it used 30.0MB. It was clear, switching from PHP5.3 to PHP5.4 saved almost 18MB of memory! That is huge!!!

TPC Memory Report
This report shows my memory usage before and after upgrading to PHP5.4. The difference is huge.

My Number One Recommendation – Upgrade PHP

Based on these findings, my number one suggestion to reduce WordPress memory usage is to upgrade from PHP5.3 to PHP5.5 or greater on your server (assuming you are running on Linux). PHP5.4 is already old and getting out of date. The savings are incredible. I have verified this on two sites so far, and multiple users have told me the same thing – see the comments below!

If you are on shared hosting like GoDaddy, 1&1, Dreamhost, etc., there is often a button in the control panel to upgrade. Simple as that.

If you are running your own Linux server, it’s more complicated. Here is an article describing what I did to upgrade from PHP5.3 to PHP5.4 on Amazon AMI. (This procedure also works for upgrading to PHP5.5).  Note that there are other solutions to reducing PHP memory usage like Xcache. I’m considering that to be an advanced solution beyond the scope of this article.  If you want to try that, go for it and let me know how it goes in the comments!

Be sure to re-test your site and plugins after you upgrade, as there might be some old code not compatible with PHP5.5.  I have done this on five WordPress sites so far with no problems though.

But Don’t Forget..

Of course, it also helps to delete unused plugins. If you want, you can install the Server IP & Memory Usage Display plugin and deactivate plugins on at a time to see their contribution to your memory usage. (Just remember to deactivate it when you’re done, because it contributes to memory usage as well). I can almost guarantee you that none will save you 18MB like switching to PHP5.5 or greater might do! But, eliminating plugins might be just enough to stop your memory errors from happening.

If you are not able to upgrade to PHP5.5+, and you can’t delete any more plugins, then you can always increase your allowable memory usage and/or get more memory for your server like the vast majority of articles recommend. The Server IP & Memory Usage Display plugin will tell you how much memory is allocated to WordPress (usually 40MB) and to PHP (usually 64MB or 128MB). You can Google around to see how to increase these limits.

But, I prefer to solve the root cause of the problem rather than treat the symptoms!

I hope my experience was helpful to you. Please comment on your findings and experiences about WordPress memory usage! – Brian

Update: PHP7

PHP7 is out, and more and more hosting companies are offering it. WP Engine reports that upgrading to PHP7 can give you a 30-50% improvement in memory consumption (relative to what previous version, I don’t know).  But, it seems like it’s worth a try!

43 thoughts on “My #1 Trick to Drastically Reduce WordPress Memory Usage

  1. Hi All Super Technical Person,

    Hope you are doing great.

    I am getting CPU and RAM issue with WordPress running on RedHat machine.
    Current system Configuration:
    RAM: 8GB
    OS : RedHat
    PHP: 5.5
    Mysql: RDS

    Below are the error details:

    Out Of Memory: kill Process 4890 (httpd) score 174 or sacrifice child
    killed process 4890 (httpd) total-vm:3328056kB, anon-rss:1334320kB, file-rss:0kB, shmem-rss:68kB
    oom_reaper: reaped process 4890 (httpd), now anon-rss:0kB, file-rss:0kB, shmem-rss:72kB

    Please help me how to fix this error.
    Also getting High CPU and Ram Utilization and web application goes down frequently

  2. WordPress in general compared to some other popular CMS just uses a really high amount of RAM. My WP sites consume between 150Mb to 400Mb of RAM each, but my PyroCMS or Expression Engine sites consume between 10Mb and 40Mb.

    So I believe WP RAM usage needs addressing far more than anything else.

    1. Hi Laurence,

      The WP core doesn’t use nearly that much memory. You either have a memory-hogging theme or plugins, or some server setting issues. I would believe that WP uses more memory than other CMS’s though.

      Best,
      Brian

    1. Hi,

      I don’t know of a way to see plugin memory usage, other than deactivating them one at a time and measuring total memory usage. If you find an easier way, let me know.

      Thanks,
      Brian

      1. Hi Brian,

        Thanks for your kind reply. but where to go and see the memory usage stats? my hosting provider provided me only 32M memory limit. so i unable to use maximum plugins. if it hits the maximum limit. i am getting a fatal error exhaust memory limit.

        Thanks in advance

        1. You would have to install a plugin, like the one I mentioned in this article.

          Also, make sure you are using the latest version of PHP, which would be in your hosting provider’s admin panel.

          Brian

  3. Helo brian..
    Few words from my experiences..

    1. By choosing to switch to the newest php version is not the only solution but its true does the job.

    2. To make low consume processing to ur server u need to think again what plugins do u use, some ppl will use extra security plugin for their wp cms web n this will make higher server processing so at least we need to use good cache processing system too we can use wp cache plugin or else we can install stand alone cache system in our server or else we can use cdn for better speed n low processing too.

    3. We can use mariadb instead of mysql.

    4. We can choose better dns provider. By using internal server dns system it actually make the server getting heavy to work.

    5. No need to use external resources plugin such as social media sharing button esc.

    Thx

  4. Brian – this worked wonders. I was able to reduce the size of my site from 104MB to just under 40MB. Thank you SO MUCH for this guide!!!

  5. Thank you so much for posting this – WP can be such a minefield sometimes! I’ve had the same problem after uploading another plugin and since I couldn’t really part with any other, I took the plunge and updated the PHP from 5.3 to 5.5. So far so good and the memory has gone from 97% to 57% instantly.

  6. Wow! After looking for hours through forums, Stackoverflow and the like I was fed up since none of the solutions there worked. And this “hack”, simple as that, magically solved the memory issue, thank you a lot!

  7. Had a small query.
    My website is currently utilising around 120MBs of RAM after the update of PHP to 5.5.
    Is that normal?
    When I wrote my last comment here, I just had updated to 5.5, it was around 60 MB.
    What are your thoughts?

    1. HI Dev,

      Hmmm, that seems strange. Try deactivating your plugins and reactivating one by one to isolate the offender.

      Best,
      Brian

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