- APC : APC (Alternative PHP Cache) is a PHP OP code cache. It is a very quick win when working with PHP and can offer a great performance boost when using Drupal. It is very much a “set it and forget it” type of application which can just be installed, enabled and left to do it’s thing.
- Memcache : Drupal's support for memcache is really good and easy to implement.There is a memcache drupal module(https://drupal.org/project/memcache) to integerate the memcache on the site.
- Varnish : When you have a lot of anonymous users reverse proxy cache can save you a lot of server load. Varnish is one of the more popular solutions within the Drupal world. Varnish sits in front of your web server application, for example Apache, Nginx or lighttpd, and can run on the same server or a remote server.Use the varnish module to integrate the varnish on your site https://drupal.org/project/varnish
- Boost : Boost provides static page caching for Drupal enabling a very significant performance and scalability boost for sites that receive mostly anonymous traffic. For shared hosting this is your best option in terms of improving performance. On dedicated servers, you may want to consider Varnish instead. When the page is then requested it is loaded quickly, because it is coming straight from the disk and no PHP or MySQL processing is needed.See the Boost module here https://drupal.org/project/boost
- Disable Database logging module : This module logs the action performed on the site to the database.Use syslog module which is also in drupal core.Using syslog you can also write the more technical log entires to the server's standard log on the file system and save the database queries.
- Enable Page & Block Cache : Enable Drupal caching (Administer > Configuration > Performance). When enabled, Drupal will render the page and associated blocks once, and then save that result in the database. This can drastically reduce the number of database calls run on a page since the results are pre-rendered. Drupal’s caching engine is most effective for anonymous visitors – if your site is mostly “read only” and doesn’t have visitors logging in, caching can make a dramatic improvement in site load speed.
- Increase Cache Lifetime : An option for some sites may be to increase the cache lifetime. This determines how long Drupal will hold onto a cached result before it will re-generate the page. If you have frequently changing content, you may want to set the cache lifetime to only 5 minutes, but if your content doesn’t change often, an acceptable value may be several hours.The cache lifetime depends on your site usage.
- Disable Un-used Modules from the site .
if you have done all the performance tips written above and you are still getting the performance problems then either get the suggestions from the High performance drupal group https://groups.drupal.org/high-performance
There are also some of the related performance related articles.See there links below