Load balancing: Is the technique of sharing work load among many resources so no single resource gets over loaded!
e.g DNS Load balancing -is to distribute requests to different servers though resolving the domain name to different IP addresses of servers, Database Load balancing - is to balance database access requests among cluster of database servers, in order to achieve database scalability and high availability
memcached: High performance, memory-object caching, used in speeding up dynamic web applications by reducing the number of time the database has to be read.
Must reads on Drupal Performance
1. Essential performance tuning for Drupal web sites by Nadeau software consulting -- This article is FAB! Just what we need to do for a drupal site!!
2. Drupal performance by Dries Buytaert
3. Scaling with MySQL replication
4. Optimizing Apache and PHP
5. Server tuning Consideration - from Drupal Handbook