WP-Cache & WP-Super Cache Increasing CPU Usage
I’m trying to help somebody fine tune their WordPress install on a VPS and suggested that they try either WP-Cache or WP-Super-Cache to lessen the load that the blog creates on the server. Upon trying this, both plugins actually seem to drive the load up considerably and crash their VPS. I’m sure it’s a plugin conflict, but I was curious to know if anyone else had seen this behavior – and if so, what they did to remedy it.
I appreciate any guidance you can provide and will be glad to give anyone more info if necessary.
Which version of the supercache are you using? It seems like it’s getting upgraded every day so you may want to check on it.
To be honest, at the beginning it will raise load levels as those static pages need to be generated first. if this is a new blog or one with low traffic, I’d just leave it alone.
So the guy I’m helping out has filled me in on the info you’ve asked about. It would appear that 0.5.1 is the version he is running – and he’s been upgrading since 0.1 trying to make the issue go away.
See, the problem is that I’m on a similar configuration (VPS, WordPress 2.3.1, WP-Super-Cache 0.5.1) and I’m not seeing what this guy is. The second he turns on WP-Super-Cache and WP-Cache, his usage skyrockets to the point of being absurd. I’ve seen little spikes when I enable a caching plugin, but not like this. From what I know, that spike is when he attempts to enable a caching mechanism – and since he’s not set up for that sort of usage, it crashes his server and brings down his site.
He’s sent along a list of plugins he’s had enabled, and I’m going to go ahead and paste that below:
The following plugins are now enabled on my site:
– Adsense-Deluxe 0.8
– Akismet 2.0.2
– Browser Sniff 1.10
– Chunk Urls for WordPress 2.0
– Flexible upload 1.9
– Less 1.1
– Math Comment Spam Protection 2.1
– Official Comments 1.1
– Subscribe To Comments 2.1.1
– WP-PageNavi 2.20
And these ones are also installed but I’ve disabled them for the testing we did and have decided to keep them that way:
– Favicon Manager 0.1
– FeedBurner FeedSmith 2.3
– Google XML Sitemaps 3.0.2
– Maintenance Mode 3.2
– Most Commented 1.4
– Recent Comments 1.18
– Recent Posts 1.07
– Related Posts 2.04
– WP-Polls 2.21
– WP-Polls Widget 2.21
– WP Super Cache 0.5.1
Like I said, any ideas y’all might have about this would be awesome.
boogah, if you let me, I’d like to participate on the discussion as well. I’m the guy he’s talking about. Just a quick comment about the posted graph, as it’s not showing exactly what happens and it’s far from the REAL problem. What really spikes then enabling both WP-Super Cache or WP-Cache is the memory usage (all the way up, really, off the charts), not the CPU. The CPU actually goes down. Sometimes it does spike as the graph shows, but I don’t think that’s the core of the problem we’re talking about.
rfischmann – is your VPS hosted on a NFS server? If the filesystem is mounted off a remote server then doing excessive writes could cause what you’re seeing.
@donncha: The server does utilize NFS based storage, but as I said I’m in the exact same environment and I’m not seeing the issues that rfischmann is. In fact, Super Cache works awesome on my VPS.
Boogah – what file locking mechanism are you using? flock or sem_get? Is rfischmann using the same?
@donncha: I’ve checked with our admin team and according to them we should be using flock across all of our servers.
boogah – That could be a problem. Flock doesn’t work too well with NFS, even the PHP manual page for flock() says so:
Can you try the default semaphone locking?
I have a CPU problems with my wp 2.3.1 sites on Bluehost.com.
I have not more visitors, i did not install other plugins, i did not create new/addon site.
Changes are only
2.2.2 to> 2.3.1
wp-cache to> wp-super-cache
I dont know flock or other techichal details 🙁
I hope and wait this plugin will be better & easy.
I don’t suppose you can login to your account and run “top” from the command line?
Make sure you upgraded your plugins because there were many changes between those versions of WordPress.
@donncha: So, correction. It took me a little time to get an audience with them, but the person in charge of the NFS setup here corrected me to let me know that we actually use semaphone locking by default on all of our servers here as flock isn’t that stellar with PHP.
Apologies for going down the wrong rabbit hole. I’ll let the person that gave me that info know that it was wrong. So, where do we go from here?
I’m not sure tbh. Trying to use the plugin on an NFS mounted directory is bad in the first place, but there could be minor differences between where your VPS is hosted and the other one that’s causing problems. Maybe one machine is physically closer to the NFS server. I don’t know.
Bottom line – trying to cache to an NFS directory is bad for performance.
@donncha: See, that’s the weird thing. Our VPS setups are *exactly* the same. I know this because I work for the hosting company (DreamHost) where he is having these problems and I can see the way our machines are configured.
Super Cache is an awesome extension of the now abandoned WP-Cache – and I recommend it to most of our customers running into issues. This is the only time I’ve actually seen it spike this way instead of plugging along as expected, so it’s sort of a head scratcher.
So if the guy who coded/built upon the original plugin doesn’t know, I’m not quite sure what I’m going to tell the customer – but that’s on my head. 😉
I’ll keep this thread marked as unresolved and follow it to see if anyone else might have any suggestions. Thanks for your help tho.
It seems like nobody else has any suggestions and boogah also can’t help me with this problem.
A few days ago I decided to completely remove WP-Super Cache from my server, downloaded the latest version and tried it again.
Same thing. A few minutes after enabling it (I mean 5 minutes, more or less), my Private Server at DreamHost spikes, free memory goes to 0MB, I start to see 500 Internal Server Error messages and CPU usage spikes as well.
I don’t know what to do and I really wanted to be able to user your plugin; my site is using too much resources and I can’t afford this PS at DH for too long.
I’m willing to pay you some money (please bear with me) for you to look at my problem, I’d give you FTP and Admin access to it so you could take a look. Please tell me if that’s possible and when can you do it. I’m desperate!
Thanks a lot in advance.
I’m having the same CPU spiking problems, getting shut down by my hosting provider. This started about three days ago. At that point I turned supercache on for the first time, but it hasn’t helped or hindered — the CPU spikes continue (as seen in the cpulog excerpt below — always having to do with index.php).
[20/Jan/2008:00:00:00 -0500] 184.108.40.206 rosinalippi.com /home/rosina/public_html/rosinalippi-com/weblog/index.php 0.677897
I’ve turned off most of my plugins and done everything else I could think of, read through all of the cpu discussions here on the forum.
It seems nobody has an answer. Any suggestions on what to try next?
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