Drupal is a robust content management system with hundreds of modules�add-ons that extend the functionality of Drupal core. You can do lots of things to increase the performance of your Drupal site. Let�s see a few aids.
Planning:
�Bloat� is one of the major things affecting the Drupal Website Development. Guess how? You might want to install many modules available but don�t. Plan ahead, know its uses, experiment how well they work and does it fulfil your needs. Most modules offer an �uninstall� function, but they don�t. So always test a module on a dev environment and later can delete it all and start again if needed. This will prevent storing unnecessary data storage in the database.
Updates:
Updates to Drupal core and module add-ons happen occasionally which includes performance improvements; so keeping them up to date is vital. Every update needs to carry some level of caution; test these updates before pushing them live because you never know what all features could have changed, removed or broken.
Pressflow:
Drupal 6 had many issues that restricted the some third party performance tools such as Varnish reverse proxy cache. These issues were all resolved in a distribution of Drupal called �Pressflow�. Therefore, it�s the best idea to upgrade Drupal 6 to Pressflow. All of the changes made in Drupal 6 for Pressflow were worked on by the Drupal community and later added to Drupal 7. If you are looking to build a new site using Drupal, then Drupal version 7 should be your choice.
APC:
APC (Alternative PHP Cache) is a PHP OP code cache. You can count on it for good performance! Doesn�t matter you work on either PHP or Drupal. It is very much a �set-get-go� type of application which can just be installed, enabled and left to do its thing. Many Drupal specific hosting companies will already have APC setup and running so you may even be using it without noticing.
Memcache:
Truth be told, Drupal�s support for Memcache is really good across Drupal 6 and Drupal 7, this is an advantage even if you have an older site. It has a fantastic caching system where any module can create or write to a standard cache table and then use a specific API to write to these cache tables. With these cache tables it can save large complex PHP tasks or MySQL queries, meanwhile creating more slow queries for reading and writing the cache. Memcache relieves that problem by storing all of these cache tables in memory. Sounds Great, Right?