A point on 4: Find or, in very extreme circumstances, write your own very lightweight profiler you can run on production servers. This will be a life-saver.
The bottlenecks are very rarely where you think they are. Even when they are, there is typically lots of low hanging fruit hanging around that you don't know about until you profile.
Also, you should have some sort of monitoring software running aggregating stuff like server loads, connection stats, number of db requests, memcached hits/misses, etc. Cacti I find quite good for this.
The bottlenecks are very rarely where you think they are. Even when they are, there is typically lots of low hanging fruit hanging around that you don't know about until you profile.
Also, you should have some sort of monitoring software running aggregating stuff like server loads, connection stats, number of db requests, memcached hits/misses, etc. Cacti I find quite good for this.