[jacques_chester]

Varnish is not effective in the face of Recent Comments because that widget breaks whole-page caching fatally. Every time anyone leaves a comment anywhere, the entire cache for the entire site is invalid.

When I looked at where the slow runtimes were occurring on Linode, it was always jammed on disk I/O and it was always on PHP functions that are reaching into MySQL.

In my experience the MySQL query cache + an object cache do more for sites with a Recent Comments widget than whole page caching.

As it happens, I do all of the above. And I was doing all of the above. And still getting jammed on I/O. Because MySQL likes to join on disk. Whole page caching is useful only if you prevent that from happening. It's useless if the cache is rendered invalid every few seconds on a chatty site.

[tiredofcareer]

    set beresp.ttl = 30s;

Varnish gives you your own throttle for how often you want invalidation. It's a tool specifically designed to make misbehaving apps -- i.e., that widget -- misbehave. You just have to slap the dog on the nose when it behaves. I'm just saying you could have made this work on Linode (and I have), but I do see your post-purchase rationalization at work, so I know anything I say will be fruitless anyway.

There's also the possibility that you had shitty neighbors.

[jacques_chester]

Right, and when I hosted on WPEngine and then on Pagely (and both of them choked), my users immediately piped up that the recent comments were inaccurate. In fact there were a number of page freshness anomalies which I believe were down to whole-page caching that I was frequently quizzed about by users.

If your page is basically static, then yes, whole-page caching will fly. But several of the sites under my supervision are, to quote Pagely's founder, used "like a chat room".

Edit, per your edit:

> I'm just saying you could have made this work on Linode (and I have), but I do see your post-purchase rationalization at work, so I know anything I say will be fruitless anyway.

Basically, I was there, I saw the numbers and I know why they wound up looking the way they did. I suspect that anyone in my particular situation would have evolved their approach in the same way that I have. I've been running Wordpress blogs since 2004. I feel that I've picked up some ideas on how to make it fast, but sometimes the general solutions don't work because you have a specific problem.

[tiredofcareer]

Got it. So you have users that expect to have real-time conversations in the comments on a blog, meaning you can't optimize a blog application like a blog is designed to be used, meaning you have to pay for SSDs in order to make your blog function at all because apparently MySQL can't handle N inserts/second and however many people have these conversations refreshing every ten seconds, generating a few SELECTs that are rapidly in query cache.

I completely understand how this could be a problem and how switching providers would fix it.

[jacques_chester]

Sarcasm aside, you clearly don't understand what my problem is.

1. Recent Comments invalidates every page it appears on whenever a comment is posted in any thread. In practice that means that the entire site cache is invalid. That breaks whole-page caching models.

2. This means that Wordpress will regenerate from scratch.

3. This means first of all generating the page, which joins multiple tables including TEXT fields. Because of the brilliant design of MySQL, these joins ignore indices on the joining fields and frequently the join will occur on disk.

4. The Recent Comments plugin also causes joins on disk because it too refers to tables with TEXT fields.

5. The query cache helps a lot, but the site on Linode was still observably jammed on I/O, even when MySQL was given an entire server to itself.

However, if you feel you can do it better, I am happy to engage your services as a fulltime replacement. WPEngine said they could do it for $250/month (they couldn't). Pagely said they could do it for $149/month (they couldn't). I invite your bid.

[tiredofcareer]

> Sarcasm aside, you clearly don't understand what my problem is.

Yeah, I spent this entire thread clueless about the issue you're running into, even though you spelled it out a few different times because you think I don't get it. Wordpress falls over under normal site load, film at eleven.

Since you want to switch to condescension, I'm assuming wise sir moved MySQL's tmpdir to a RAM disk and found that unsatisfactory for his mystical, MySQL-breaking SELECT/INSERT workload? Also, I'm far more expensive, and I know that WPEngine is multitenancy Wordpress on Linode in the backend. (That one's free.)

[jacques_chester]

We're not being very productive here, are we? I could nitpick your comment just now but it wouldn't change your mind either.

You think I'm an idiot. Possibly you think I'm a liar.

I don't think you're an idiot. All I can do is point out that I looked at the numbers, I've tested various strategies or tools (and adopted most of them), I referred the problem to the experts, and this is where I've had to go.

So let's just ignore each other from now on.