Max tuples that can be handled by a reducer

[Prasanth J]

Hi

I wanted to find the maximum number of tuples a reducer can handle. For that I 
am using the following inside an UDF in a sampling job

maxTuples = Runtime.getRuntime.maxMemory() / tuple.getInMemorySize();

I am little skeptical about the maxMemory() usage as it will be different in 
sampling job and the actual job. 
Does this always provide a good estimate of the max tuples a reducer can handle?

Thanks
-- Prasanth