Should I still use entitycache in Drupal 7 projects?

You are totally right that the complexity plays a role. I also have a note (from more than a year ago) which says that entitycache improved the performance about 30-40%. But all I can remember about the testing is that I measured that locally very quickly and the site is a pretty complex commerce site. :)

Now the case is that there will be a Varnish in front and not much logged in users so the entitycache module won't do a use performance impact. But like you said if it is a win (even a little win) then why not installing entitycache to every site?

I recently performed some tests around node and entity loads using a variety of caching techniques. In short I found that Entity Cache provided a large improvement when loading entities which were able to use entity cache.

In a nutshell my findings for entity load were:
- nodes are 2x slower than entities
- fields don't really slow things down too much more
- hooks on node load are probably the culprits
- mysql query cache leads to 30% improvement (if hit)
- entitycache can lead to 80% improvement
- Using APC with entitycache didn't help too much more (probably because my DB was on SSD). ie. Getting the entity from a cache table in DB still provided great results.
- You will see good results for light/heavy nodes and light/heavy entities if they are able to use EntityCache.
- Field Collections were unable to use it at time of testing.

When using xHProf on a page load I found similar results with time spent in entity load reduced. I got between 6% and 10% speedup for the entire page.
- heavy node pages reduced from 14.4% down to 4.3%
- lightweight term pages reduced from 10.0% to 4.1%.

So yes, I did see good results in my tests.

Usual caveats apply when reading these results as they are specific to my setup and data. I suggest giving XHProf a try on your own setup.

You can download my slides here:
http://morpht.com/posts/one-weird-old-tip-lose-node-weight

cheers

Murray

I recently had to disable entity cache module on a multilingual website because it needed to flush caches every time a new Node (or Other entity) was added.

In fact the site goes faster now, I don't know why.

I noticed problem with entity cache and metatag module. When I open node I saw only default metatag settings (but node has its own defined), but when cleared cache everything is OK. This problem persist (I tried manually clear all cache tables) and unexpectedly returns. I figured it out, that Entity cache is the problem, but I don't know why this happens.