There seems to be a problem in the new liferay 5.2.x versions due to the changes of
LPS-1603. This has quite some impact on the performance since the caches for web content articles are not used.
In JournalContentUtil.getDisplay() some checks are added on the portals lifecycle:
I don't know why, but the lifecycle is often empty in renderrequests which results in a false from themeDisplay.isLifecycleRender(). Which won't populate the ehcache.
You probably won't notice it when you only use web content articles on a page or all other portlets which have the setting:
in liferay-portlet.xml which is catched by the CacheFilter and will result in an immediate response from cache. You'll notice the problem only when you're page contains a portlet which doesnt allow layout caching. That was changing our request times from 15ms to 6 seconds.
We might have found another problem in the lifecycle stuff but we're still debugging that and, if needed, create another issue for that.