Very slow PHP responses? Configuring PHP-FPM?

madine

I'm looking for a bit of advice on configuring PHP-FPM/DB connections/Wordpress... I'm not sure where the problem is which is why it's a vague question.

Essentially, our Woocommerce site struggles when there's more than a single visitor. If I have a page open then middle-click a few links to open in background tabs, they resolve one after the other and their TTFBs increase 2 seconds per page load. It's almost like there's a single process sequentially responsible for every site visitor so it's very easy to get TTFB of 20 seconds with just a couple of visitors opening a few pages.

I've never used PHP-FPM before so I'm not sure what to set it at. I've had it at the default (Requests = 20, Max Child Threads = 5), I've increased child threads to 20, there didn't seem to be a difference.

I've checked the max connections in Maria and it's at 250 so... that shouldn't be an issue?

I've tried running WP with no plugins and the difference to TTFB was barely noticeable.

Running cURL against a basic phpinfo page still gives a 2 second TTFB which is what makes me think it's some kind of single process or slow process start issue.

Requesting a static CSS or HTML file gives a TTFB of <40ms which, again, points me at PHP.

I'd link the site here but, as I've said, if anyone besides me visits it, it becomes unusable.

Any advice? I'm guessing this isn't normal. I'll follow up with support but just asking here incase anyone has faced the same and has a configuration suggestion.

sean

The PHP-FPM options that you see in the dashboard don't do anything at this time.

In the past they were applied to individual PHP-FPM process pools for each application but that failed to scale with the influx of new customers and we had to switch the PHP setup to PHP-CGI, which unfortunately is a single process per request.

You can improve the performance of your WP sites a couple of ways:

Go to Plugins in your WP dashboard and install a cache plugin like W3TC, WP Super Cache, etc. This can make a huge difference.
Set up a symlink to serve media from your uploads directory. Instructions are here: Example: using a symlink app to speed up a WordPress site

We know the PHP-CGI thing isn't great for busy sites or sites that do a lot of stuff on every request and we're looking into ways to provide a separate PHP setup with better performance. Right now we do have a separate Nginx+PHP-FPM application that might help, but it doesn't include Apache features like .htaccess which a lot of sites need. If you can live with out htaccess, then give that a try.

madine

sean Unfortunately, I'm also seeing up to 2 second TTFB for PHP calls that don't touch WP such as a basic
<?php phpinfo(); ?> and when triggering, for example, 8 parallel requests, they're answered sequentially, each with an increasingly long TTFB.

The site already has a caching plugin, memcached for object caching and media is served from cloudflare. The only variables left I don't have insight on are 'time between apache receiving the call and triggering the PHP process' and 'time to make the connection between PHP and MariaDB'.

a single process per request

The behaviour I'm seeing is less like 'a single process per request' and more like 'a single process per shell user'. At the moment, nobody can visit the site if there's already someone on it.

igor

madine The behaviour I'm seeing is less like 'a single process per request' and more like 'a single process per shell user'. At the moment, nobody can visit the site if there's already someone on it.

Are you testing that from the same browser? I ask because browsers limit the number of HTTP connections with the same domain name.

sean

madine feel free to email support and we'll look into it.

madine

igor No, running the parallel tests using cURL and JMeter but also able to make the site crawl just having two different browser windows open.

madine

sean Have done. Ta.