2.9.10 Availability and performance

If a single server is responsible for name space, there is still single point of failure, and a performance bottleneck.

Most systems therefore

• Replicate name list to other servers. Also increases performance for heavily accessed parts of name space eg secondary servers in DNS
• Cache information received by lookup. No need to repeat lookup if asked for same information again. Increases performance. Implemented in both client side and server (in recursive calls) in DNS.

If information is cached, how do we know when its invalid? May attempt to use inconsistent information.