RC 6, 32/64-bit memory adjusting minecraft server launcher

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

# V1.7: Borderline case existed where memory allocation would be in error.
# Example: Survivor copy of 90, 90% => Survivor space of 100.
# Desired Eden of 250.
# Would attempt to allocate 200 for eden, 200 for two survivors.
# That's 400 for new, even if "MaxNew" was 350.

# Right behavior in this case?
# No clear answer.
# What's more important: making sure you have as much eden as you ask for,
# or limiting your "new" memory?
#
# Answer used here: "new" memory is more important than tenured,
# as long as tenured is big enough. So, if that happens, we force maxnew up to fit.
# When this happens, a warning is printed. Pay attention to your logs when this
# happens -- tenured overflow results in very large amounts of full collections
# because small collections cannot clear eden.

## V1.6. This time the 64 bit flag works.
# Again: This is throwing "too much" memory at eden/survivor.
# Pay attention to the GC log. Sections like

# 1552.959: [CMS-concurrent-reset-start]
# 1552.965: [CMS-concurrent-reset: 0.005/0.005 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
# {Heap before GC invocations=17 (full 1):
#  par new generation   total 180224K, used 146721K [0000000009000000, 0000000016c00000, 0000000025200000)
#   eden space 135168K, 100% used [0000000009000000, 0000000011400000, 0000000011400000)
#   from space 45056K,  25% used [0000000014000000, 0000000014b48750, 0000000016c00000)
#   to   space 45056K,   0% used [0000000011400000, 0000000011400000, 0000000014000000)
#  concurrent mark-sweep generation total 102400K, used 63696K [0000000025200000, 000000002b600000, 000000003b000000)
#  concurrent-mark-sweep perm gen total 24940K, used 21197K [000000003b000000, 000000003c85b000, 0000000044600000)

# The "CMS-concurrent-reset" means it has finished a full collection.
# The "concurrent mark-sweep generation" line has the tenured allocation
# In this case, 63 MB of long-term data.

# Sections like

# 56.089: [GC 56.089: [ParNew
# Desired survivor size 41523608 bytes, new threshold 4 (max 4)
# - age   1:   17033216 bytes,   17033216 total
# - age   2:   22458216 bytes,   39491432 total
# - age   3:      14552 bytes,   39505984 total
# - age   4:     136648 bytes,   39642632 total

# 17 MB of temporary space was recently allocated; just under 40 MB of temporaries are "surviving"
# and not immediately useless. (This comes from startup; almost all of that will be valid for the life
# of the program run.)

# Age 4 overflows (age 4's total larger than the max, or worse, "new threshold 2" or other small number)
# means the potential for tenured space to grow unnecessarily. This kills long-term performance.

## V1.5-corrected: 64 bit version, and ** LOTS OF MEMORY ALLOCATION **
# This is to give information for data collection.
# Determine how much your system uses, and then adjust numbers down to avoid waste
#
# Specifically: By making the memory pools large, we see how much is used.
# Then, we can determine what to cut them down to.
#
# This will probably be the last CMS version; G1GC next.

java=/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Commands/java

## V1.4: Java is now customizable (see the above line), thank you oracle for a
## java (1.7) that does not support 32 bit servers for reduced memory consumption.

## V1.3: The -XX:SoftRefLRUPolicyMSPerMB=0 flag got lost! Back in now.
## This flag defaults to 1000, and can cause memory leaks.

## 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. (NB: apparently only 1.5 gb on microsoft windows?)
# 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

JVM_SIZE="-d32 -server"
# JVM_SIZE="-d64 -XX:+UseCompressedOops -server"

# CMSInitiatingOccupancyFraction: Determine how frequently to do a full CMS
# Special: New "Most important". This primarily affects long-term growth
# of the heap. The percentage of used space before CMS starts a collection.
# 95 is sufficient for general stuff. 85 is useful for things that suddenly
# need a lot.
# Dynamic maps, in particular, no longer needs 125 MB of survivor -- it can
# get by with 60-75. It can go much lower, but then the garbage collections
# need to be started sooner, or else it will never have enough memory and
# always grow the heap.
#
# To clarify: This is obsolete -- completely -- in G1GC.
# This needs to be low enough that sudden spurts of temporary memory trigger
# garbage collection first.
# This should be re-worked as a "MB safety level" -- for example, if you have
# 300 MB of tenured, and want at least 30 MB free. But Java don't work that way.
# As tenured increases, this will also increase the "keep free" level.
CMSInitiatingOccupancyFraction=80

# 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=1300

# 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=500

# Most important tuning number. Survivor.
# Making this higher: Fewer full collections, but more wasted space.
# During startup, expect this to overflow frequently.
# 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 **
# (worse, it will cause tenured space to grow.)
# ** TOO BIG WILL WASTE SPACE **
# (this is a minor issue overall.)
#
# To clarify: You can easily use 12 here if you stay primarily in one place.
# You can even use less, but the memory savings are not significant.
# Biggest usage I've seen: dimension travel (see below) and dynamic maps with
# low angle (20 degree) maps.
#
# *** Recommendations
# If you do a lot of dimension travel -- including using a nether hub to get
# around, or lots of Mystcraft books (two links to go from A to B in the same
# world), then you want 65 MB if you can afford it, or 53 MB minimum. That's
# for one person; groups will be higher.
# (tested in a world with forests at the hub zone; may be higher for extreme hills,
# jungles, or jungle-hills (expected to be the worst case.))
#
# If you do a lot of high speed rail travel over large distances, a minimum of
# 40 MB. Ditto if you use a lot of flight mode movement. More if you have a
# speed boost.
#
# If you do very little travel -- if you are just building in one spot -- then
# 15 MB is plenty.
#
# If you are testing a new mod pack, and have no clue what you need, start at 100.
# If you are working with a multiplayer server, I don't know what to advise --
# test and tell me.

# SurvivorCopySize=65
SurvivorCopySize=100

# 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 (implies lots of block
# updates), 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 98% 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. Remember, teleportation
# will raise this value very rapidly.
#
# To clarify the problem: An overflow here forces memory into tenured space. If tenured is
# nearly full -- lets say Java will start a garbage collection soon -- then this can force
# more space to be allocated to tenured.
#
# Forcing more space into tenured is the disaster that this is all about preventing.
# Tenured space is more expensive to collect, and Java does not release this back to the
# operating system when it does not need it. This means, on systems that are doing more than
# just a minecraft server (say, a client, a browser, perhaps voice chat software, etc), this
# will impact your whole system's performance.
#
# A secondary effect of overflow is forcing earlier/more frequent full collections.
# For single/dual processors, this may be the more dominant factor.
# For 4/8 core processors, this is minor.

# 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 Survivor. Java requires it to be
# an integer multiple of Survivor.

desiredEden=250

# Summary: Approximately desiredEden, plus 2 times Survivor,
# plus 130, 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".
#
# 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 sufficient -- specified eden.
NEW=$desiredNew
RATIO=$desiredRatio

# borderline case: Not quite the desired eden, we ran into maxnew.
# Disable these; we'd rather raise maxNew for Minecraft.
## NEW=$biggerNew
## RATIO=$MaxRatio

### 1.7 bug fix! Turns out that borderline cases could fail.
if ( [ $NEW -gt $MaxNew ] )
then
    MaxNew=$NEW
    ## CAUTION! "Start" below may fail.
    ## If you get here, then you need to watch out for tenured overflow
    echo "** Launcher adjusted MaxNew; make sure tenured space is big enough"
fi

START=$(($NEW + 130))
# Experimal behavior: Starting up, and loading one person into a world, takes
# 130 MB of tenured space to have Java "happy". Less just results in repeated
# full collections while Java raises the amount of allocated memory.

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

# A few more notes ...

# -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.

# -XX:CompileThreshold: Tells Java when to convert bytecode into compiled code.
# Server defaults to something like 15,000, which is appropriate for something that will
# run for months, and horrible for something that will run for a few hours.
# Non-server defaults to ... 1000? 1500? Much lower.

exec $java \
    $JVM_SIZE \
    -Xms${START}m -Xmx${MAX}m \
    -XX:NewSize=${NEW}m -XX:MaxNewSize=${MaxNew}m \
    -XX:+UseAdaptiveGCBoundary \
    -XX:SurvivorRatio=$RATIO \
    -XX:TargetSurvivorRatio=$TargetSurvivorRatio \
    -XX:CompileThreshold=3000 \
    -XX:CMSInitiatingOccupancyFraction=$CMSInitiatingOccupancyFraction \
\
    -XX:SoftRefLRUPolicyMSPerMB=0 \
    -XX:MaxPermSize=150m \
    -XX:+UseConcMarkSweepGC -XX:+UseParNewGC \
    -XX:MaxHeapFreeRatio=20 \
    -XX:MinHeapFreeRatio=15 \
    -XX:+DisableExplicitGC \
    -XX:MaxTenuringThreshold=4 \
    -XX:+PrintHeapAtGC -XX:+PrintTenuringDistribution \
    -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -Xloggc:GC.log \
    -jar new_server.jar nogui 151myst10.3

# The last word of that exec statement -- '151myst10.3' -- 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).