92209431 Java Performance

7/28/2019 92209431 Java Performance

1/20

JAVA MEMORY MANAGEMENT

GARBAGE COLLECTION TUNING +SIZING MEMORY GENERATIONS


2/20

OVERVIEW

Theory and concepts:

JVM memory areas

GC

Tuning

SAP standards

Tools for logfile analysis

HPJMeter

JVMStat

SAP Memory Analyser

Case Study

Discussion


3/20

JAVA VS C++

# include < string>

int main ( int argc, cha r ** argv)

{

int i;string * var;

for (i = 0; i < 1000; i + + )

{

var = new string (memory leaking or not);delete (var);

}


4/20

JAVA VS C++

import java.lang.String;

public sta tic void main ( String [] a rguments)

{

int i;String var;

for (i = 0; i < 1000; i + + )

{

var = new String (memory never lea king);}

}


5/20

TOWARDS HOTSPOT JVM


6/20

HOTSPOT JVM


7/20

HOW DOES GC WORK


8/20

HOW DOES GC WORK


9/20

HOW DOES GC WORK


10/20

HOW DOES GC WORK


11/20

GC LOGGING -verbose:gc

[GC 325407K->83000K(776768K), 0.2300771 secs]

[GC 325816K->83372K(776768K), 0.2454258 secs]

[Full GC 267628K->83769K(776768K), 1.8479984 secs]

-XX:+PrintGCDetails

[GC [DefNew: 64575K->959K(64576K), 0.0457646 secs] 196016K->133633K(261184K), 0.0459067 secs]]

-XX:+PrintGCTimeStamps

111.042: [GC 111.042: [DefNew: 8128K->8128K(8128K),

0.0000505 secs]111.042: [Tenured: 18154K->2311K(24576K),0.1290354 secs] 26282K->2311K(32704K), 0.1293306 secs]

Logfile:


12/20

GC LOGGING

-XX:+PrintTenuringDistribution

1096.789: [GC 1096.789: [ParNew Desired survivor size 86232268 bytes, new threshold 6 (max12)

- age 1: 50754696 bytes, 50754696 total

- age 2: 12147696 bytes, 62902392 total

- age 3: 12295552 bytes, 75197944 total-age 4: 6537136 bytes, 81735080 total

- age 5: 2435944 bytes, 84171024 total

- age 6: 3013488 bytes, 87184512 total

- age 7: 627368 bytes, 87811880 total

- age 8: 999536 bytes, 88811416 total

- age 9: 924656 bytes, 89736072 total

- age 10: 1811480 bytes, 91547552 total

: 554848K->89528K(561792K), 0.5317388 secs] 607743K->146164K(1217152K) icms_dc=18 ,0.5326526 secs]


13/20

PERFORMANCE CONCEPTS

TROUGHPUT: % of runtime in GC

PAUSE

FOOTPRINT

PROMPTNESS


14/20

GC DESIGN

SERIAL vs PARALLEL

CONCURRENT vs STOPTHEWORLD

COMPACTING vs NONCOMPACTING vsCOPYING


15/20

FOUR GARBAGE COLLECTORS

Default Collector

-XX:+UseParallelGC

-XX:UseConcMarkSweepGC

-Xincgc


16/20


17/20

PARALLEL GC

Minor collections only

+2 Processor machines -> Overhead

Fragmentation Tenured generation

Stop the World Full GC -> Performance Trap

-XX:ParallelGCThreads=


18/20

CONCURRENT

Parallel Minor GC

Concurrent Full GC

Fragmentation

Minors during Full Collections Memory + resource intensive -> free thread

Future to overcome Performance Trap

Large Tenured Generation High Troughput, low pauses, lower footprint, better

promptness


19/20

TUNING GUIDELINES Use tools to get an idea of the applications lifetime distribution

++ objects alive during GC = longer pauses

Young Generation Guarantee

++ Eden space and Survivor spaces:

Fast collection because more dead object Less collections does not equal longer pauses

Less copying

Less often full collections + faster full collections

More processors = more memory needed (esp Eden)

Set memory sizes optimal, test a GC, retune memory sizes

Performance trap non scalability of JVM


20/20

SAP SETTINGS

Sapnote 723909

-verbose:gc

-XX:+PrintGCDetails

-XX:+PrintGCTimeStamps

-XX:NewSize = -XX:MaxNewSize

-XX:PermSize = -XX:MaxPermSize (256m 512m)

-Xms = -Xmx = 2048 MB (170m Dispatcher + 50m per extra server)

-XX:NewSize = 1/6 Xmx (1/3 Dispatcher)

-Xss2m

-XX:SurvivorRatio=2

-XX:TargetSurvivorRatio=90

-XX:+UseParNewGC

-XX:+PrintTenuringDistribution

-XX:MaxTenuringThreshold=31

-XX:+UseTLAB

-XX:+UseConcMarkSweepGC

-XX:DisableExplicitGC

92209431 Java Performance

Documents