자바 성능 강의

Java Perfor-mance Tuning조대협

인사 !!

조대협

• 개발자• 웹로직 기술 지원 엔지니어• 장애 진단 , 성능 튜닝• 컨설턴트 (SOA,EAI,ALM,Enterprise 2.0)• 아키텍트 ( 대용량 분산 시스템 )• APAC 클라우드 수석 아키텍트• 프리렌서• 지금은 Chief(Cheap?) 아키텍트

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ICEBREAK

질문 : 성능이란 ??

• 안나오면 파트장님한테 깨지는 것• 다음은 그룹장님에게 깨지는 것• 막판은 실장님에게 소환 당하는 것• 동시에 처리할 수 있는 트렌젝션의 양과 ,

응답시간 . (TPS & Response Time)

오늘은 ?

• 성능 엔지니어링• 자바 애플리케이션의 병목 구간 발견• JVM 튜닝• 잡다한 자바 성능팁

성능 엔지니어링

• 언제 ?


• 접근 방법• 문제의 정의 : 느려요 (X)

• Break down ( 구간 )• Isolate• Narrow down• Bottleneck 발견• 해결


• 필요한것은 ? 도구 : 부하테스트 도구 , 모니터링 도구 , 프로파일링 도구

역량 : FIN_WAIT 가 모지 ?

전문 지식 : 내부구조가 어떻게 되지 ?

경험 그리고 집요함 !! 이것이 포인트 !! ( 여기서

다 갈림 )

Chapter 1. 자바 애플리케이션의 병목 구간 찾아내기

일반적인 자바 서버 애플리케이션의 구조

User AP

WAS

JVM DBMSWeb Server

Network

Client

Legacy

기본지식

• 쓰레드 풀링

Thread Pool

Idle Thread(Waiting)

request

Thread Pool

Working Thread(Handling request)

request

response

Thread Pool

Working Thread

기본 지식

• 자바 쓰레드 상태 전이

Runnable

newstart

BlockedSleep/done sleep

Wait/no-tifySuspend/Re-sume

Block on IO/IO complete

dead

stop

<< Thread State Diagram >>

- Runnable : running- Suspended,Locked : waiting on monitor entry / waiting on condition /MW- Wait : Object.Wait()

일반적인 자바 서버의 구조

• 대부분 비슷WebServerOR BrowserOR Client

Dispatcher

Request Queue

ThreadPool

ConnectionPool

Thread Queue

JMS Thread Queue

APP1 Thread Queue

APP2 Thread Queue

Other ResourcesConnector

Working Thread

IdleThread

대부분 Queue + Thread Pool 구조(Tomcat,Jboss,WebLogic 등 )

쓰레드 덤프

• Thread dump– Snapshot of java ap (X-ray)– We can recognize thread running

tread state by “continuous thread dump”

Slow down in WAS & User AP

• Getting Thread Dump– Unix : kill –3 pid , Windows : Ctrl + Break– Get thread dump about 3~5 times be-

tween 3~5secsThreads

Time

Working thread

Thread dump


• Thread dump– It displays all of thread state by

“THREAD STACK”

"ExecuteThread: '42' for queue: 'default'" daemon prio=5 tid=0x3504b0 nid=0x34 runnable [0x9607e000..0x9607fc68]

at java.net.SocketInputStream.read(SocketInputStream.java:85) at oracle.net.ns.Packet.receive(Unknown Source) at oracle.net.ns.NetInputStream.getNextPacket(Unknown Source) at oracle.net.ns.NetInputStream.read(Unknown Source) at oracle.net.ns.NetInputStream.read(Unknown Source) at oracle.net.ns.NetInputStream.read(Unknown Source) at oracle.jdbc.ttc7.MAREngine.unmarshalUB1(MAREngine.java:730) at oracle.jdbc.ttc7.MAREngine.unmarshalSB1(MAREngine.java:702) at oracle.jdbc.ttc7.Oall7.receive(Oall7.java:373) at oracle.jdbc.ttc7.TTC7Protocol.doOall7(TTC7Protocol.java:1427) at oracle.jdbc.ttc7.TTC7Protocol.fetch(TTC7Protocol.java:911) at oracle.jdbc.driver.OracleStatement.doExecuteQuery(OracleStatement.java:1948) at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:2137) at oracle.jdbc.driver.OraclePreparedStatement.executeUpdate(OraclePreparedStatement.java:404) at oracle.jdbc.driver.OraclePreparedStatement.executeQuery(OraclePreparedStatement.java:344) at weblogic.jdbc.pool.PreparedStatement.executeQuery(PreparedStatement.java:51) at weblogic.jdbc.rmi.internal.PreparedStatementImpl.executeQuery(PreparedStatementImpl.java:56)

Thread name Thread id (signature)Thread State

Program stack of this thread

Sun JVM


• How to analysis thread dumpMYTHREAD_RUN(){ 1 call methodA();} methodA(){

//doSomething(); 2 call methodB();} methodB(){

//call methodC(); 3}

methodC(){

// doSomething 4 for(;;){// infinite loop } 5}

“MYTHREAD” runnable 1at …MYTHREAD_RUN(): “MYTHREAD” runnable 2at …methodA() at …MYTHREAD_RUN(): “MYTHREAD” runnable 3at …methodB()at …methodA()at …MYTHREAD_RUN(): “MYTHREAD” runnable 4at …methodC()at …methodB()at …methodA()at …MYTHREAD_RUN():

“MYTHREAD” runnable at …methodC()at …methodB()at …methodA()at …MYTHREAD_RUN():

계속 이모양이반복됨

Source codeThread dumps


• CASE 1. Lock contention– In the java application java thread wait

for lock in synchronized method– Occurred in multi threaded program– Reduce frequency of synchronized

method– Synchronized block must be imple-

mented to be end as soon as possible (※ IO? )

public void synchronized methodA(Object param){ //do something while(1){}}

< sample code >


• CASE 1. Lock contention

Thread1 Thread3

Thread2

Thread4

Sychronized MethodA

Threads

Time

Thread1 – That has a lock

Thread 2.3.4 – waiting for lock


• CASE 1. Lock contention : Thread dump example"ExecuteThread: '12' for queue: 'weblogic.kernel.Default'" daemon prio=10 tid=0x0055ae20 nid=23 lwp_id=3722788 waiting for monitor entry [0x2fb6e000..0x2fb6d530]

:at java.lang.ClassLoader.loadClass(ClassLoader.java:255)

:at org.apache.xerces.jaxp.SAXParserFactoryImpl.newSAXParser(Unknown Source)at org.apache.axis.utils.XMLUtils.getSAXParser(XMLUtils.java:252)- locked <0x329fcf50> (a java.lang.Class)

"ExecuteThread: '13' for queue: 'weblogic.kernel.Default'" daemon prio=10 tid=0x0055bde0 nid=24 lwp_id=3722789 waiting for monitor entry [0x2faec000..0x2faec530]

at org.apache.axis.utils.XMLUtils.getSAXParser(XMLUtils.java:247)- waiting to lock <0x329fcf50> (a java.lang.Class) :

"ExecuteThread: '15' for queue: 'weblogic.kernel.Default'" daemon prio=10 tid=0x0061dc20 nid=26 lwp_id=3722791 waiting for monitor entry [0x2f9ea000..0x2f9ea530]

at org.apache.axis.utils.XMLUtils.releaseSAXParser(XMLUtils.java:283)- waiting to lock <0x329fcf50> (a java.lang.Class)at


• CASE 2. Dead lock– CWC “Circular waiting condition”– Commonly it makes WAS hang up– Remove CWC by changing lock direction– Some kind of JVM detects dead lock au-

tomatically

sychronized methodA(){ call methodB();}sychronized methodB(){ call methodC();}sychronized methodC(){ call methodA();}

< sample code >


• CASE 2. Dead lock

Thread1

Sychronized MethodA

Thread2

Sychronized MethodB

Thread3

Sychronized MethodC

Threads

Time

Thread 1

Thread 2

Thread 3

Circular waiting condition


• CASE 2. Dead lockFOUND A JAVA LEVEL DEADLOCK:----------------------------"ExecuteThread: '12' for queue: 'default'": waiting to lock monitor 0xf96e0 (object 0xbd2e1a20, a weblogic.servlet.jsp.JspStub), which is locked by "ExecuteThread: '5' for queue: 'default'""ExecuteThread: '5' for queue: 'default'": waiting to lock monitor 0xf8c60 (object 0xbd9dc460, a weblogic.servlet.internal.We-bAppServletContext), which is locked by "ExecuteThread: '12' for queue: 'default'" JAVA STACK INFORMATION FOR THREADS LISTED ABOVE:------------------------------------------------Java Stack for "ExecuteThread: '12' for queue: 'default'":========== at weblogic.servlet.internal.ServletStubImpl.destroyServlet(ServletStubImpl.java:434) - waiting to lock <bd2e1a20> (a weblogic.servlet.jsp.JspStub) at weblogic.servlet.internal.WebAppServletContext.removeServletStub(WebAppServletContext.java:2377) at weblogic.servlet.jsp.JspStub.prepareServlet(JspStub.java:207) : Java Stack for "ExecuteThread: '5' for queue: 'default'":========== at weblogic.servlet.internal.WebAppServletContext.removeServletStub(WebAppServletContext.java:2370) at weblogic.servlet.jsp.JspStub.prepareServlet(JspStub.java:207) at weblogic.servlet.jsp.JspStub.prepareServlet(JspStub.java:154) - locked <bd2e1a20> (a weblogic.servlet.jsp.JspStub) at weblogic.servlet.internal.ServletStubImpl.getServlet(ServletStubImpl.java:368) : Found 1 deadlock.========================================================

Deadlock auto detect in Sun JVM


• CASE 2. Dead lock"ExecuteThread-6" (TID:0x30098180, sys_thread_t:0x39658e50, state:MW, native ID:0xf10) prio=5at oracle.jdbc.driver.OracleStatement.close(OracleStatement.java(Compiled Code))at weblogic.jdbc.common.internal.ConnectionEnv.cleanup(ConnectionEnv.java(Compiled :

"ExecuteThread-8" (TID:0x30098090, sys_thread_t:0x396eb890, state:MW, native ID:0x1112) prio=5at oracle.jdbc.driver.OracleConnection.commit(OracleConnection.java(Compiled Code))at weblogic.jdbcbase.pool.Connection.commit(Connection.java(Compiled Code)) :

sys_mon_t:0x39d75b38 infl_mon_t: 0x39d6e288: oracle.jdbc.driver.OracleConnection@310BC380/310BC388: owner "ExecuteThread-8" (0x396eb890) 1 entry 1)

Waiting to enter: "ExecuteThread-10" (0x3977e2d0) "ExecuteThread-6" (0x39658e50)

sys_mon_t:0x39d75bb8 infl_mon_t: 0x39d6e2a8: \ oracle.jdbc.driver.OracleStatement@33AA1BD0/33AA1BD8: owner "ExecuteThread-6" (0x39658e50) 1 entry 2)

Waiting to enter: "ExecuteThread-8" (0x396eb890

Deadlock trace in AIX JVM


• CASE 3. Wait for IO Response– Situation in waiting for IO response

(DB,Network)– Commonly occurred caused by DB lock-

ing or slow responseThreads

Time

Wait for IO response


• CASE 3. Wait for IO Response"ExecuteThread: '42' for queue: 'default'" daemon prio=5 tid=0x3504b0 nid=0x34 runnable [0x9607e000..0x9607fc68] at java.net.SocketInputStream.socketRead(Native Method) at java.net.SocketInputStream.read(SocketInputStream.java:85) at oracle.net.ns.Packet.receive(Unknown Source) at oracle.net.ns.NetInputStream.getNextPacket(Unknown Source) at oracle.net.ns.NetInputStream.read(Unknown Source) at oracle.net.ns.NetInputStream.read(Unknown Source) at oracle.net.ns.NetInputStream.read(Unknown Source) at oracle.jdbc.ttc7.MAREngine.unmarshalUB1(MAREngine.java:730) at oracle.jdbc.ttc7.MAREngine.unmarshalSB1(MAREngine.java:702) at oracle.jdbc.ttc7.Oall7.receive(Oall7.java:373) at oracle.jdbc.ttc7.TTC7Protocol.doOall7(TTC7Protocol.java:1427) at oracle.jdbc.ttc7.TTC7Protocol.fetch(TTC7Protocol.java:911) at oracle.jdbc.driver.OracleStatement.doExecuteQuery(OracleStatement.java:1948) at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:2137) at oracle.jdbc.driver.OraclePreparedStatement.executeUpdate(OraclePreparedStatement.java:404) at oracle.jdbc.driver.OraclePreparedStatement.executeQuery(OraclePreparedStatement.java:344) at weblogic.jdbc.pool.PreparedStatement.executeQuery(PreparedStatement.java:51) at weblogic.jdbc.rmi.internal.PreparedStatementImpl.executeQuery(PreparedStatementImpl.java:56) at weblogic.jdbc.rmi.SerialPreparedStatement.executeQuery(SerialPreparedStatement.java:42) at com.XXXX 생략 at ……..


• CASE 4. High CPU usage– When monitoring CPU usage by

top,glance. WAS process consumes a lot of CPU - almost 90~100%

– Find it using tools below• Sun : prstat,pstack,thread dump• AIX : ps –mp,dbx,thread dump• HP : glance,thread dump• See a document “How to find bottleneck in

J2EE application “ in http://www.j2eestudy.co.kr

http://www.j2eestudy.co.kr/


• CASE 4. High CPU usage– Example in HP UX

HP glance

1. Start “glance”2. Press “G” and enter the

WAS PID3. Find the TID that con-

sumes a lot of CPU re-source

4. Get a thread dump5. Find the thread in Thread

dump that has a matched LWID with this TID

6. And find the reason and fix it


• Summarize– Thread dump is snapshot of Java Appli-

cation.– If u meet a slowdown situation, Get a

thread dump.– Analysis thread dump.– And fix it..

결론은…

이것저것 어려우시면 그냥 툴을 사서 쓰세요 . !!Jennifer APM

Chapter 2. JVM 튜닝

Generational Garbage Collection

JVM Memory Layout

• New/Young – Recently created object• Old – Long lived object• Perm – JVM classes and methods

Eden Old Perm

New/Young Old

Used in Application App binary

Total Heap Size

SS1 SS2

Garbage Collection

• Garbage Collection– Collecting unused java object– Cleaning memory– Minor GC

• Collection memory in New/Young generation

– Major GC (Full GC)• Collection memory in Old generation

Minor GC

• Minor Collection– New/Young Generation– Copy and Scavenge – Very Fast

Minor GC

Eden SS1 SS1

Copy live objects to Survivor area

New Object

Garbage

Lived Object

1st Minor GC

Old

Old

Old

Minor GC

2nd Minor GC

Old

Old

Old

New Object

Garbage

Lived Object

Minor GC

OLD

3rd Minor GC

Objects moved old space when they become tenured

New Object

Garbage

Lived Object

Major GC

• Major Collection– Old Generation– Mark and compact– Slow

• 1st – goes through the entire heap, marking unreachable objects• 2nd – unreachable objects are compacted

Major GC

Eden SS1 SS2

Eden SS1 SS2

Mark the objects to be removed

Eden SS1 SS2

Compact the objects to be removed

Server option versus Client option

• -X:NewRatio=2 (1.3) , -Xmn128m(1.4), -XX:NewSize=<size> -XX:MaxNewSize=<size>

GC Tuning Parameter

• Memory Tuning Parameter– Perm Size : -XX:MaxPermSize=64m– Total Heap Size : -ms512m –mx 512m– New Size

• -XX:NewRatio=2 Old/New Size• -XX:NewSize=128m• -Xmn128m (JDK 1.4)

– Survivor Size : -XX:SurvivorRatio=64 (eden/survivor)– Heap Ratio

• -XX:MaxHeapFreeRatio=70• -XX:MinHeapFreeRatio=40

– Suvivor Ratio• -XX:TargetSurvivorRatio=50

Support for –XX Option

• Options that begin with -X are nonstandard (not guaran-teed to be supported on all VM implementations), and are subject to change without notice in subsequent releases of the Java 2 SDK.

• Because the -XX options have specific system require-ments for correct operation and may require privileged ac-cess to system configuration parameters, they are not rec-ommended for casual use. These options are also subject

to change without notice.

Garbage Collection Model

• New type of GC– Default Collector– Parallel GC for young generation - JDK 1.4– Concurrent GC for old generation - JDK 1.4 – Incremental Low Pause Collector (Train GC)

Parallel GC

• Parallel GC– Improve performance of GC– For young generation (Minor GC)– More than 4CPU and 256MB Physical

memory required

threads

timegc

threads

Default GC Parallel GC

Young Generation

Parallel GC

• Two Parallel Collectors– Low-pause : -XX:+UseParNewGC

• Near real-time or pause dependent application• Works with

– Mark and compact collector– Concurrent old area collector

– Throughput : -XX:+UseParallelGC• Enterprise or throughput oriented application• Works only with the mark and compact collector

Parallel GC

• Throughput Collector– –XX:+UseParallelGC– -XX:ParallelGCThreads=<desired number>– -XX:+UseAdaptiveSizePolicy

• Adaptive resizing of the young generation

Parallel GC

• Throughput Collector– AggressiveHeap

• Enabled By-XX:+AggresiveHeap• Inspect machine resources and attempts to set various parameters to be op-

timal for long-running,memory-intensive jobs– Useful in more than 4 CPU machine, more than 256M– Useful in Server Application– Do not use with –ms and –mx

• Example) HP Itanium 1.4.2 java -XX:+ServerApp -XX:+AggresiveHeap -Xm-n3400m -spec.jbb.JBBmain -propfile Test1

Concurrent GC

• Concurrent GC– Reduce pause time to collect

Old Generation– For old generation (Full GC)

– Enabled by -XX:+UseConcMark-SweepGC

threads

timegc

threads

Default GC Concurrent GC

OldGeneration

Incremental GC

• Incremental GC– Enabled by –XIncgc (from JDK 1.3)– Collect Old generation whenever collect young generation– Reduce pause time for collect old generation– Disadvantage

• More frequently young generation GC has occurred.• More resource is needed• Do not use with –XX:+UseParallelGC and –XX:+UseParNewGC

Incremental GC

• Incremental GC

Minor GC

After many time of Minor GC

Full GC

Minor GC

Minor GC

Old Generation is collected in Minor GC

Default GC Incremental GC

Young Generation

OldGeneration

Incremental GC

• Incremental GC-client –XX:+PrintGCDetails -Xincgc –ms32m –mx32m

[GC [DefNew: 540K->35K(576K), 0.0053557 secs][Train: 3495K->3493K(32128K), 0.0043531 secs] 4036K->3529K(32704K), 0.0099856 secs][GC [DefNew: 547K->64K(576K), 0.0048216 secs][Train: 3529K->3540K(32128K), 0.0058683 secs] 4041K->3604K(32704K), 0.0109779 secs][GC [DefNew: 575K->64K(576K), 0.0164904 secs] 4116K->3670K(32704K), 0.0169019 secs][GC [DefNew: 576K->64K(576K), 0.0057541 secs][Train: 3671K->3651K(32128K), 0.0051286 secs] 4182K->3715K(32704K), 0.0113042 secs][GC [DefNew: 575K->56K(576K), 0.0114559 secs] 4227K->3745K(32704K), 0.0191390 secs][Full GC [Train MSC: 3689K->3280K(32128K), 0.0909523 secs] 4038K->3378K(32704K), 0.0910213 secs][GC [DefNew: 502K->64K(576K), 0.0173220 secs][Train: 3329K->3329K(32128K), 0.0066279 secs] 3782K->3393K(32704K), 0.0325125 secs

Young Generation GC Old Generation GC in Minor GC TimeMinor GC

Full GC

Sun JVM 1.4.1 in Windows OS

Garbage Collection Measurement

• -verbosegc (All Platform)• -XX:+PrintGCDetails ( JDK 1.4)• -Xverbosegc (HP)

Garbage Collection Measurement

• -verbosegc

[GC 40549K->20909K(64768K), 0.0484179 secs][GC 41197K->21405K(64768K), 0.0411095 secs][GC 41693K->22995K(64768K), 0.0846190 secs][GC 43283K->23672K(64768K), 0.0492838 secs][Full GC 43960K->1749K(64768K), 0.1452965 secs][GC 22037K->2810K(64768K), 0.0310949 secs][GC 23098K->3657K(64768K), 0.0469624 secs][GC 23945K->4847K(64768K), 0.0580108 secs]

Full GC

Total Heap Size

GC Time

Heap size after GC

Heap size before GC

GC Log analysis using AWK script

• Awk script

BEGIN{ printf("Minor\tMajor\tAlive\tFree\n");}{ if( substr($0,1,4) == "[GC "){ split($0,array," "); printf("%s\t0.0\t",array[3])

split(array[2],barray,"K") before=barray[1] after=substr(barray[2],3) reclaim=before-after printf("%s\t%s\n",after,reclaim) }

if( substr($0,1,9) == "[Full GC "){ split($0,array," "); printf("0.0\t%s\t",array[4])

split(array[3],barray,"K") before = barray[1] after = substr(barray[2],3) reclaim = before - after printf("%s\t%s\n",after,reclaim) } next;}

% awk –f gc.awk gc.log

※ Usage

gc.awk

Minor Major Alive Freed0.0484179 0.0 20909 196400.0411095 0.0 21405 197920.0846190 0.0 22995 186980.0492838 0.0 23672 196110.0 0.1452965 1749 422110.0310949 0.0 2810 192270.0469624 0.0 3657 194410.0580108 0.0 4847 19098

gc.log


< GC Time >

GC Log analysis using HPJtune

※ http://www.hp.com/products1/unix/java/java2/hpjtune/index.html

http://www.hp.com/products1/unix/java/java2/hpjtune/index.html


< GC Amount >

Garbage Collection Tuning

• GC Tuning– Find Most Important factor

• Low pause? Or High performance?• Select appropriate GC model (New Model has risk!!)

– Select “server” or “client”– Find appropriate Heap size by reviewing GC log– Find ratio of young and old generation

Garbage Collection Tuning

• GC Tuning– Full GC Most important factor in GC tuning

• How frequently ? How long ?• Short and Frequently decrease old space• Long and Sometimes increase old space• Short and Sometimes decrease throughput by Load balancing

– Fix Heap size• Set “ms” and “mx” as same• Remove shrinking and growing overhead

– Don’t• Don’t make heap size bigger than physical memory (SWAP)• Don’t make new generation bigger than half the heap

Tools

• Visual VM

Tools

• Visual VM

쓰레드 상태 모니터링

Tools

• Visual VM

패키지별 , CPU 사용량 모니터링

Example

Example

2004-01-08 오후 7:14

2004-01-09 오전 8 시 전후

2004-01-09 오후 7 시 전후

금요일 업무시간

2004-01-10오전 10 시 전후

2004-01-10오후 6 시 전후

PEAK TIME52000~56000 sec9 시 ~ 1 시간 가량

Before TunedOld Area

Example

Peak Time 시에 Old GC 시간이 4~8 sec 로 이로 인한 Hang 현상 유발이 가능함

Before TunedGC Time

Example

12 일 03:38A12 일 05:58P13 일 07:18A13 일 09:38P14 일 11:58A15 일 01:18A15 일 03:38P16 일 05:58A16 일 07:18P17 일 08:38A17 일 10:58P

Weekend

Mon Office

Our

Tue Office

Our

Thur Office

Our

Fri Office

Our

After AP TunedGC Time

Example

12 일 03:38A12 일 05:58P13 일 07:18A13 일 09:38P14 일 11:58A15 일 01:18A15 일 03:38P16 일 05:58A16 일 07:18P17 일 08:38A17 일 10:58P

Weekend

Mon Office

Our

Tue Office

Our

Thur Office

Our

Fri Office

Our

Chapter 3. 잡다한 자바 코딩 성능 팁들 .

자바 코딩팁

• 잡다하지만 기본 적인 것들 적절한 Synchronized StringBuffer ( “+” vs append) Collection (Vector,List) 등은 사이즈를 초기화 하여 사용 Collection 보다는 Array. (Collection 은 사이즈가 변동되는

경우만 ) Collection 은 편하지만 알고 쓰세요 .!! (Synchronized 되어

있을 수 있음 ) DB 는 Index 필수 (DBA 에게 Profiling 부탁 !!. Slow

Query 튜닝 ) DB 는 Connection Pooling 필수 고성능은 DB Write/Read DB 분리 캐쉬 !! ( 할수있는건 다하자 !!- 파일 , 데이타… ) 대부분 IO 문제 - 파일 , 네트워크 ,DB 마이크로 벤치 마크 !! 필수 !!

자바 코딩팁

• Logging!!!! FILE IO. 전체 성능의 5~10% SL4J + LogBack 이 대세

• FILE IO FileWriter + BufferedWriter. ( 테스트해보고 하세요 ..)

Application Server

• HTTP 1.1 Keep Alive• DB Connection Pooling• 적절한 Working Thread 수• 불필요한 Logging 자제 !!

감사합니다 . :)

자바 성능 강의

Technology