5.2.1 Problem
You need to figure out how much memory a name server will require.
5.2.2 Solution
While this answer may seem like a cop-out, the only sure-fire way to determine how much memory a name server will need is to configure it, start it, and then monitor it using a tool like top. After a week or so, the size of the named process should stabilize, and you'll know how much memory it needs.
5.2.3 Discussion
The reason it's so difficult to calculate how much memory a name server requires is that there are so many variables involved. The size of the named executable varies on different operating systems and hardware architectures. Zones have a unique mix of records. Zone data files may use lots of shortcuts (e.g., leaving out the origin, or even using a $GENERATE control statement) or none at all. The resolvers that use the name server may send a huge volume of queries, causing the name server's cache to swell, or may send just sporadic queries.
5.2.4 See Also
The BIND 9 ARM, section 2.3.
Getting Started
Zone Data
BIND Name Server Configuration
Electronic Mail
BIND Name Server Operations
Delegation and Registration
Security
Interoperability and Upgrading
Resolvers and Programming
Logging and Troubleshooting
IPv6