wp_ewwwio_media_optimize_cron

You won’t find that exact name because is is built from two different parts in different files. It is used to do background image optimization when you upload images. It checks every five minutes to see if anything is left in the queue for processing.

Is this something the plugin does per default or something you can turn on/off in the settings? Where in the code is this job run?

It’s default/normal behavior. Background optimization cannot be disabled by the user, but is disabled automatically when a compatibility conflict is detected (if you’ve found one I don’t know about, I’m all ears).
Parallel optimization can be disabled if it is using too many resources.

It’s just the first site I’ve noticed this cron event on and I’m trying to debug why that current site sometimes returns random timeouts. I figured that it *could* this job if its run every 5 minute.

Is this a heavy process? The site have arround 3-4k images.
Is there a place in the code where I can see exactly what the plugin is trying to run?

No, it isn’t a heavy process unless you’ve uploaded some images. That could cause some temporary problems with the aforementioned parallel optimization, but otherwise that cron job is very lightweight.

The more likely culprit related to EWWW is if a plugin is generating images at page load time, causing EWWW to spring into action and optimize those. Here’s how you check for that:

1. Turn on EWWW’s debug option
2. wait for 24 hours (or less if you have a very active site)
3. On the dashboard browse to Media->Dynamic Image Debugging, and see what it shows.

If you have a bunch of images with multiple re-optimizations, then you have a problem with another plugin/theme. If you don’t know how to read a trace log, post a couple here via pastebin and I’ll take a look.

I will try that and get back to you if the problems are related to EWWW. Thank you!