Databases basically come in 4 sizes:

1= The entire DB fits into memory.
2= The performance critical table(s) fit(s) into memory
3= The indexes of the performance critical table(s) fit into memory.
4= Neither the performance critical tables nor their indexes fit into memory.

Performance decreases (exponentially), and development + maintenance 
cost/difficulty/pain increases (exponentially), as you go down the list.

While it is often not possible to be in class "1" above, do everything you can 
to be in at least class "3" and do everything you can to avoid class "4".

At ~$75-$150 per GB as of this post, RAM is the cheapest investment you can 
make in a high perfomance, low hassle DBMS.  IWill's and Tyan's 16 DIMM slot 
mainboards are worth every penny.


-----Original Message-----
Sent: Oct 27, 2005 3:31 PM
Subject: [PERFORM] How much memory?

Is there a rule-of-thumb for determining the amount of system memory a 
database requres (other than "all you can afford")? 

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