Pin Apache Cassandra compaction threads to a core

pin-compaction.sh

#!/bin/bash
# A quick & dirty script to pin compaction threads to a core without
# any consideration for HT or what kind of compaction any given thread
# is doing.
# atobey@datastax.com 2015-08-02

# match all processes with nice value 4, which is hard-coded in Cassandra
pids=$(ps -eLo nice,tid,args |awk '/^ *4 .*java/{print $2}')

ncores=$(grep ^processor /proc/cpuinfo |wc -l)

offset=1
for pid in $pids
do
        core=$(($ncores - $offset))
        offset=$(($offset + 1))
        if [ $offset -gt $ncores ] ; then
          offset=1
        fi
        
        taskset -pc $core $pid
        ionice --class 3 --pid $pid
done