I am trying to understand which ORM is fast in performance?
Can someone please explains me pros and cons of this ORM and which one to choose for application performance boost.
The problem with "big" ORM tools such as EF or NHibernate, is that (exagerating?) 99% of developers are overwhelmed with mastering simply how to make it work; they don't have time to figure out how to make it perform. Worse, making these tools perform properly usually boils down to having competent SQL/Database design and tuning skills - which weakens a major selling point of the ORM.
The issue with Level 2 caching, in my opinion, is eclipsed by the other performance losses a poorly-used ORM introduces. It seems most projects using an ORM are doing a poor job of it (along with a poor job of designing the database), which makes level 2 caching somewhat moot.
As a consequence, micro-ORM tools like Massive or Dapper (the latter is used by Stack Overflow) are very attractive:
To be clear, a well-used macro ORM is a great thing. Do you have the highly experienced staff to ensure that it is well-used?
The bottom line is this: if you think a full-scale ORM will safely hide database complexity, almost assuredly you'll be mistaken. If I'm given a choice I would go with a micro ORM. Don't get me wrong, I think EF and NHIbernate are very cool and I'm jazzed to use them - I'm just saying you need to manage your expectations.