How can i identified Best number of Mappers and Reducers in my cluster

[Sivaji]

Hi Every one,

In my organisation we are using 6 node cluster, i am running some pig scripts on more then 10 m of records, i want set no.of mappers and reducers, 

HOW can i know how many reducers i can set for my pig script ? what is the best performance of mappers size ? i am using below code to set mapps and reducers,

SET default_parallel 200;

SET mapred.min.split.size 256000;

SET mapred.max.split.size 256000;

SET pig.noSplitCombination true;

SET mapred.max.jobs.per.node 1; 

Thanks