Load spikes – any ideas?

Hey all, sorry for not replying sooner. One of the clients and I are no longer working together. The other one seems to have been completely fixed by doubling the RAM on their hosting instances from 4GB to 8GB each.

Does this seem like a lot for a site that has wp-super-cache and about 16k visits a day?

That’s a lot of memory! Chances are there’s a memory hogging plugin running on the server somewhere.

I found a company (no affiliation) online a while back when this was an issue for a friend of mine.

citrusleaf.net/clsolutions.html

Hi folks,
I encountered almost exactly the same issue with a WP site as well.

Obviously just adding more RAM isn’t the solution– I mean at some point WP is going to bomb once it uses up 8gb of RAM, so adding RAM only seems to postpone the inevitable server crash.

Any other sage advice?

Thanks,
Jim

Are you using Feedburner and the utm_source GET parameters to track where visitors come from? Unfortunately Supercache doesn’t cache those requests so visitors from Twitter or feed readers will visit those URLs and they won’t be cached.
Check out Joost’s comment on this post about the issue. (That feature has since been removed from Supercache) And check out Google Analytics plugin. I should make this a FAQ…

Oh, it already is in the dev version!

To be clear, you can use the debug mode in W3TC to understand which queries are expensive and may block php for returning so apache can answer requests. W3TC and WPSC use the same performance advantages of using disk for apache, so using W3TC with page caching to memcached is not going to perform like using disk enhanced when compared to WPSC when using a single server. Memcached is ideally suited for either persistent storage across web server restarts or across multiple servers. Anyway, you’ll want to find your expensive queries and optimize for them so you can build your page cache efficiently, and object caching should reduce the number of queries that are ultimately made.

If the single change made, without being in conjunction with anything else, was adding RAM, and that solved your issues, then RAM was your problem. Either your services were badly configured, or there was not enough RAM for the services to serve your website.

8GB would be excessive for most, but it is very difficult to judge without some solid facts. Essentially, you need to measure how much RAM is being used, and by what and when.

There are many factors.

@frederick I’ve also found that sites that generate large pages are sometimes not well suited to memcached. It works better with many (many!) small buckets rather than several large ones.

By default memcached has a 1MB slab size, so if for some reason you’re not using compression (the default) and you still have a huge page (often due to comments) that is greater than 1MB when compressed, you will have lots of cache misses.

We found it. core control http logging was turned on and then forgotten. wp_posts: 300,000 records at 3.6 GB.
turned off and cleaned the table. Site is running very well now.

Can you clarify what you mean by:
core control http logging
?

Thanks.

Can you clarify what you mean by:
core control http logging

https://www.ads-software.com/extend/plugins/core-control/

We found it. core control http logging was turned on and then forgotten.

I’ve done that myself, and fully intend on adding a admin notice alert to mention it’s enabled for the next release..