What is the best cacher for drupal (Boost, xcache or varnish)?

What is the best caching method (cach开发者_运维问答er) for Drupal, taking in consideration logged in and anonymous users? is it Boost, XCache,or Varnish? I need a comparison between them.

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Varnish is output cache and saves more than 50% queries to Mysql server. also it allows for a grace period to serve expired cache objects if you experience failure of your back-end
xCache it caches your PHP code on-the-fly transparently saving on compile time next time the same code is run. it is used for Opcode cache + storing Datastore
Boost provides static page caching for Drupal enabling a very significant performance and scalability boost for sites that receive mostly anonymous traffic

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Varnish is super good as frontend server -- running Drupal site under proxy server. Varnish should not run with boost.

Memcache should also used to reduce alot of query to mysql.