Release candidate, memory adjusting minecraft server launch

#!/bin/bash
# This line is for starting from mac os icon double click
cd "$( dirname "$0" )"

## V1.2: We now play with -XX:TargetSurvivorRatio=n to reduce waste in new, permitting more
## space to be used

# Configurables:
# -d32 is for heap size up to 2.5gb.
# Change to "-d64 XX:+UseCompressedOops" if you use more.
# ** Mention that flag specifically, do not rely on it being autoset.
# ** Known and documented JVM bug -- https://forums.oracle.com/forums/thread.jspa?messageID=10017916

# CMSInitiatingOccupancyFraction: Determine how frequently to do a full CMS
# sweep. Lines like:
# 1308.811: [Full GC (System) ...
# indicate "CMS failure". This means a full "pause the app and full GC".
# Too many: Lower the percentage.
# Too low a percentage: More CMS full sweeps (looks like:)
# 171.808: [GC [1 CMS-initial-mark: 212329K(367040K)] ...
# and usually many, many more lines after that, ending with
# 173.156: [CMS-concurrent-reset: 0.003/0.003 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
# Note the time stamps between those.

# -XX:+UseAdaptiveGCBoundary -- apparently, adjust the boundary between new and tenured as needed.
# Nice to see; did not know about it before.
# Sadly, it seems to have no effect.

# -XX:+CMSIncrementalMode: Tells the garbage collector to break the job into many small parts.
# May result in better performance. Essential on systems with few cores.

# Memory tuning:
# Command line controls total heap, and "new". "Tenured" is the difference.
# Bigger "new": Less frequent collections.

# These numbers are in "Megabytes", the java "m" suffix.

# The rule of memory tuning:
# SurvivorSpace * (SurvivorRatio + 2) = New
# ("SurvivorSpace" is twice the actual surviving threshold.)
# SurvivorSpace * SurvivorRatio = Eden.
# Two additional survivor spaces are used to copy surviving objects across minor collections.

# MAX: Maximum heap space used.
# Does not include permanent (byte/compiled code)
# Does not include JVM overhead
MAX=800

# Tenured: Desired long-term storage space
# Will vary based on mods, and "loaded chunks"
# -- how many parties of players close to each other.
#
# Starting assumption: 250 for 1 person, plus 50 per group
# of players near each other.
#
# That is a guess. Please report what numbers work for your server.
Tenured=350

# Most important tuning number. Survivor.
# Making this higher: Fewer full collections, but more wasted space.
# During startup, expect this to overflow frequently.
# Dynamic maps wants this at least 100, preferrably 125.
# Actual space allocated is 2 spaces, each one twice this size.
# "waste/overhead" will be two about to three times this number.
# *** Maximum of 1/6rd of "new"
# Pay attention to the tenuring distribution logs.
# *** This should be enough for generation 3 95%+ of the time. ***
# ** TOO SMALL WILL KILL YOUR GARBAGE COLLECTION **
# ** TOO BIG WILL WASTE SPACE **
SurvivorCopySize=12

# Survivor target ratio. Java defaults to 50%, which wastes a lot of space. If you know how much
# you need (see below), you can set this value higher; this gives less waste and "better performance".

TargetSurvivorRatio=90

## Notes on "SurvivorCopySize":
# Flying around in creative mode, in already generated chunks will want
#   at least 30-35, preferrably 40 meg.
# Standing around, single player, can be happy with less than 1.
# Even in Mystcraft, with massive amounts of decay everywhere, 95% of the time 1 meg suffices.
# Moving around a little, doing basic building/digging, about 3.
#
# The rule: You want to see "new threshold 4 (max 4)" most of the time.
# The total value at age three --
# - age   3:      36712 bytes,    5897520 total
# should be less than this 95% of the time.
# 12 meg is more than enough for one person with EBXL, Mystcraft, Twilight Forest,
# and Custom Ore Gen. Even in EBXL's extreme jungle with Mystcraft's decay littering the ground.
#
# The single biggest factor is chunks loaded; that will depend more on parties than on players,
# and the speed at which they move. Adjust to your server, and your mods.
#
# Single player won't need that much. Really.

# Second most important tuning. Eden.
# Making this bigger means less frequent small collections.
# General rule: Make this as big as your memory can handle.
# Must be at least 2x SurvivorCopySize. Java requires it to be
# an integer multiple of that value.

desiredEden=100

# Summary: Approximately desiredEden, plus 2 times Survivor,
# plus 100, will be used by java to start the heap. Up to a max of MAX.
# Script will attempt to ensure at least Tenured space exist;
# should exit with a message if it cannot.
#
# In theory, Java will allocate extra space to new or tenured as needed.
# In practice, I've never seen it increase "new".
# ** Update! Just found a config flag conflict, and updated.
# I suspect I've now gotten it to increase "new" as demand goes up.
#
# See the bottom of the config section for more.

# If your shell cannot do math, replace these with an appropriate constant

MaxNew=$(($MAX - $Tenured))

## Survivor=$((2 * $SurvivorCopySize))
## Working with survivor target. "2" is for 50%. For 90%, it's much closer to 1.
## What we want is 100 / target percentage, as the ratio instead of 2.
## For integer only shell math, we re-write as (100 * survivor) / target, which gives us
## close integer to the desired result -- as close as we can get in the shell.

Survivor=$(( ($SurvivorCopySize * 100 ) / $TargetSurvivorRatio ))

## Equally, the "3" in sanity test is from 3 bins -- two survivors, one eden.
## But that does NOT change here -- it's still the sanity test lower limit.

sanityTest=$((3 * $Survivor))
if [ $sanityTest -gt $MaxNew ]
then
    echo Memory config error >& 2
    exit 1
fi

# We cannot use more than MaxNew.

# The idea:
# 1. Find the multiple of Survivor that is bigger than S and less than MN.
# 2. Determine survivor ratio from that. Subtract 2 (java.)
# 3. Specify -Xmn for new, and survivor ratio, to set eden and new.

# "New" will be Eden plus 2* Survivor.

# MaxRatio -- what the ratio is if we use all of maxnew.
MaxRatio=$(( ($MaxNew / $Survivor) - 2 ))
# DesiredRatio -- what the ratio is based on declared eden space
# There is no "-2" here -- this will allocate eden plus 2* survivor.
desiredRatio=$(( ($desiredEden / $Survivor)  ))

# SurvivorSpace * (SurvivorRatio + 2) = New

# Now check for "desired Eden". If survivor is not an exact multiple of DE,
# then we have just rounded down. Test for this, and if so, see if we can
# raise it up (watch out for maxnew)

## TODO! FIXME! This is a cheap approximation
if ( [ $(( $desiredRatio + 1 )) -le $MaxRatio ] )
then    desiredRatio=$(( $desiredRatio + 1 ))
fi

desiredNew=$(($Survivor * ($desiredRatio + 2) ))
biggerNew=$(($Survivor * ($MaxRatio + 2) ))

echo Debug: Max ratio $MaxRatio, desiredRatio $desiredRatio
echo Debug: biggerNew $biggerNew, should be less than MaxNew $MaxNew
echo Debug: desired eden $desiredEden, survivor $Survivor, actual new $desiredNew

# desiredNew: Gives an eden up to, not bigger, than desiredEden.
# biggerNew: Gives an eden at least as big as desiredEden.
# FIXME: DesiredNew / ratio should be smallest at least as big as desiredEden
# This means, if less, then add 1 to ratio and add to new.
#
# "Bigger" assigns ALL non-tenured memory to new.

# Q: Desired numbers? Bigger/Max numbers?

# Choose one of these pairs

# New space is small -- specified eden.
NEW=$desiredNew
RATIO=$desiredRatio

# Tenured is small -- specified tenured space.
## Should Not Be Needed -- "NewSize" and "MaxNewSize" specified separately.
# In theory, Java should now adjust new as neeed.
#NEW=$biggerNew
#RATIO=$MaxRatio

START=$(($NEW + 100))

## TESTME: Does "MaxNewSize" matter if we have adaptive GC boundary? Does it hurt?

exec java \
    -d32 -server \
    -Xms${START}m -Xmx${MAX}m \
    -XX:NewSize=${NEW}m -XX:MaxNewSize=${MaxNew}m \
    -XX:+UseAdaptiveGCBoundary \
    -XX:SurvivorRatio=$RATIO \
    -XX:TargetSurvivorRatio=$TargetSurvivorRatio \
    -XX:CompileThreshold=3000 \
        -XX:CMSInitiatingOccupancyFraction=95 \
\
        -XX:MaxPermSize=150m \
    -XX:+UseConcMarkSweepGC -XX:+UseParNewGC \
    -XX:MaxHeapFreeRatio=20 \
    -XX:MinHeapFreeRatio=15 \
    -XX:MaxTenuringThreshold=4 \
    -XX:+PrintHeapAtGC -XX:+PrintTenuringDistribution \
    -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -Xloggc:GC.log \
    -jar new_server.jar nogui 147test

# The last word of that exec statement -- '147test' -- is just something that shows up in
# the process list, so I can tell which process is which server (each copy of this script
# has a different name in that field).