TYPO3 Core

We've discovered a major performance issue in all version since at least 6.2 up to 7.6 (previous versions might be affected too):

The TypoScript configuration options to concatenate and compress CSS/JS files triple page render time if the page isn't fully cached. For example, render time increases from 350ms to over 1000ms in our installation.

This is the case if at least one frontend plugin on this page is configured that its output shouldn't be cached. It seems that for every request, the files are checked for modifications and maybe the files are re-processed. The only way to ensure that page render times reasonable is to enforce these TypoScript settings (esp. when the bootstrap_package is installed):

config.concatenateCss = 0
config.compressCss = 0
config.concatenateJs = 0
config.compressJs = 0

To fix the issue, compressed/concatenated files should only be created if they aren't available and clearing the cache should remove the compressed/concatenated files.