One common server bottleneck is DNS lookups. Many common server tasks such as from looking up hostnames to write Apache logfiles and processing incoming mail require the use of DNS queries. If you're running a high-traffic system it might be useful to cache previous lookups.

There are several different packages you can use for caching DNS requests - including bind, djbdns, dnsmasq and pdnsd.

The pdnsd package is a very simple and lightweight tool for DNS caching. It will, like many of the other systems, act as a small DNS server forwarding requests to a "real" DNS server and caching the responses.

When pdnsd is stopped it will save all the lookups which have been made against it so they may be reloaded when it starts again.

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