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Admin Slow with CSS Merge Enabled

Admin Slow with CSS Merge Enabled

After performance tuning one of our Magento 2 sites, we noticed a drastic slow down in the Magento admin site.


After tediously testing our server configuration (NGINX, Perconna, PHP7), we were able to attribute the slowness to the site configuration. The verified cause of the issue is the CSS merge setting (Admin > Stores > Configuration > Developer > CSS Settings > Merge CSS Files).


To isolate this setting as the cause, I create a stock Magento 2.02 droplet at Digital Ocean from their one-click applications. About 5 minutes later, we’re up and running with a completely stock testing environment. On the stock settings (CSS not merged), it takes the admin Dashboard 3.65 seconds to load on this server (2 CPU, 1GB RAM).


Next, we changed turned on CSS merge. Voila! After clearing the cache to remove the alert message, the admin Dashboard page takes 33.46 seconds to load the page.


To recap:

  • CSS Merge Off – 3.65s
  • CSS Merge On – 33.46s

That’s nearly a 1000% increase, for anyone that cares about the math.


We also saw it take 1.2m to load the admin products page after the default product load.



Anyone else seeing similar results?

Tags (1)

Re: Admin Slow with CSS Merge Enabled

CSS merging is a onetime operation for a Magento 2 site.

It reduces page load time for a new visitor, because the visitor's browser will do a single request for CSS resources instead of multiple.

Re: Admin Slow with CSS Merge Enabled

 Dmitry, do you have the same issue with Magento 2? Your post was unclear. Good that you got your links in there, though. ;-)

Re: Admin Slow with CSS Merge Enabled

Im Experiencing same problem. Very slow backend - not only first load pages, all pages - all loads. This is on M2.0.2, PHP 7, MariaDB 10 and Apache.

Re: Admin Slow with CSS Merge Enabled

Does disabling CSS merge speed it back up?

Re: Admin Slow with CSS Merge Enabled

I have this same issue... disabling merge css site goes back fast...


Any idea how to fix this issue?