jheap

#!/bin/bash

#
# Prints the number of MB in the Old Generation and how many
# MB are consumed by top memory-consuming classes.
#
# Usage: jheap [-gc] process_id
#
# -gc will cause a GC to be triggered just before the measurement
#
# NOTE: If you're running in Linux, due to a ptrace bug, you might have to run the following
# before this will work properly:
#
# echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope
#

die() {
  echo "$1"
  exit 1
}

die_missing_id() {
  die "Process id required (-h for help)"
}

if [[ -z $1 ]]; then
  die_missing_id
fi

if [[ $1 == "-h" ]]; then
  echo "Usage: jheap [-gc] process_id"
  exit 0
fi

if [[ $1 == "-gc" ]]; then
  if [[ -z $2 ]]; then
    die_missing_id
  fi
  process_id=$2
else
  process_id=$1
fi

if [[ $(jps | grep "^$process_id " | wc -l | awk '{ print $1 }') != "1" ]]; then
  die "No such Java process: $process_id"
fi

if [[ $1 == "-gc" ]]; then
  jcmd $process_id GC.run > /dev/null 2>&1
fi

jmap -heap $process_id 2> /dev/null |grep -A2 "Old Generation"|tail -1|awk '{ mb = $3 / 1024 / 1024 ; printf("%.1f MB used by old generation\n" , mb) }'
jmap -histo $process_id|grep " [[:digit:]]\{7\}  \S"|awk '{ num = $2 ; mb = $3 / 1024 / 1024 ; class = $4 ; printf("%.1f MB used by %s instances of %s\n", mb, num, class) }'|sort -nr