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From Bryan Keller <brya...@gmail.com>
Subject Max mappers and reducers
Date Sun, 04 Sep 2011 01:41:45 GMT
Is there any rule-of-thumb for setting the maximum number of mappers and reducers per task
tracker, via the mapred.tasktracker.xxx.tasks.maximum properties? I have data nodes with 24-cores
(4 CPUs w/ 6 cores) and 24 GB RAM. I have the child processes using -Xmx1024m, so 1 GB each.

I currently have the maximums set to 16. This potentially will result in 32 processes (16
mappers and 16 reducers), so more processes than cores and more potential memory use than
physical memory. However, it also potentially leaves resources unused if I am running a map-only
job, in which only 16 mapper processes will be used, so 8 cores and 8 GB aren't doing much.

What have others been setting these values to, and for what hardware?


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