An In-Depth Examination of Java I/O Performance

and Possible Tuning Strategies

Kai Xu xuk@cs.wisc.edu

Hongfei Guo guo@cs.wisc.edu

Outline

• Why bother? (Problems)

• Our goals

• Java I/O overview

• Tests design

• Test results and analysis

• Conclusions

Why bother?

• Growing interest in using Java

• Much works had been done in Java

performance evaluation but• NOT in Java I/O

Our Goals

• Is it really bad (Compared with C/C++)

• How bad

• Possible tuning strategies

• How well they work

Random AccessFile

OutputStream InputStream

FileOutputStream

FilterOutputStream

ByteArrayOutputStream

BufferedOutputStream

DataOutputStream

FileInputStream

FilterInputStream

ByteArrayInputStream

BufferedInputStream

DataInputStream

An Overview of Java I/O Classes

Test Design

• Access patterns

Sequential write/read

Random write/read

• Data interested

Elapse time, CPU breakdown

• Comparison group: C/C++

Test Design (continued)

• Tests on basic Java I/O strategies

Test 1: The lowest level I/O

Test 2: Buffered I/O

Test 3: Direct buffering

Test 4: Operation size

Test 5: Java JNI

Test Setup

• Hardware configurationCPU: Pentium III 667 MHz

Memory: 128 MB

Disk: 10 GB IDE

• Software configurationOS : Redhat 6.2

JVM : JDK 1.2.2

• Profiling Tools: PerfAnal profiler, gprof profiler 2.9.5, time

Test 1: The lowest level Java I/O

• Test parameters:

buffer size : 0 Byte

operation size : 1 Byte

• Sequential Write/Read

• Random Write/Read

Sequential Write/Read

0

100

200

300

400

500

600

700

800

0 10 20 30 40 50 60 70 80 90 100

File Size (M)

Ela

pse

Tim

e (s

)

C

Java

Breakdown -- File size: 100M

0

50

100

150

200

250

300

350

400

read write etc.cpu other

Tim

e (

s)

C

Java

0

50

100

150

200

250

1 2 3 4 5 6 7 8 9 10

File Size (M)

Ela

ps

e T

ime

(s

)

C

Java

Random Write/Read

Breakdown -- File size: 10M

0

10

20

30

40

50

60

70

read w rite seek other cpu w aiting

Tim

e (s

)

CJava

Test 1 Analysis

• Java raw I/O: 200%x slower

• Java system calls cost more read : 224%x write: 158%x

• Random Access is similar

Test 2: Buffered I/O in Java

• Test parameters:

buffer size : 1024 Bytes

file size : 100 MB

• Sequential Write/Read

• Buffering Strategies: No Buffering:

(FileInputStream/FileOutputStream) BufferedInputStream/BufferedOutputStream Direct Buffering

Buffering Strategies in Java

0

100

200

300

400

500

600

700

800

Total Seq Write Seq Read

No Buffer

Buffered Stream

Direct Buffer

CPU Breakdown

0

20

40

60

80

100

120

140

160b

uff

er.

rea

d

bu

ffe

r.w

rite

re

ad

wri

te

arr

ay

co

py

Tim

e (

s)

BufferedStream

Direct Buffer

Test 2 Analysis

• Buffering improves I/O reducing system calls

• Buffered Stream: ~25%

• Direct Buffering: ~40% special purpose vs. general purpose

• No buffering for random access

Test 3: Direct Buffering

• Test parameters:

file size : 100 MB

operation size : 1 Byte

• Sequential Write/Read

• Random Write/Read

Sequential Write/Read

0

100

200

300

400

500

600

700

800

0 2 4 6 8 10 12

Buffer Size (2^x Bytes)

Ela

ps

e T

ime

( s

)

C

Java

Breakdown – Java

0

50

100

150

200

250

300

350

400

450

500

16B 32B 64B 128B 256B 512B 1K 2K 4K 1M 10M

Buffer Size

Tim

e (

s)

other

etc. CPU

memcpy

read

write

Breakdown – C

0

20

40

60

80

100

120

16B 32B 64B 128B 256B 512B 1K 2K 4K 1M 10M

Time (s)

Bu

ffer

Siz

e

wait

etc. CPU

memcpy

read

write

Random Write/Read

0

100

200

300

400

500

600

700

800

900

0 2 4 6 8 10 12

Buffer Size (2^x Bytes)

Ela

pse

Tim

e (s

)

C

Java

Breakdown – Java

0

100

200

300

400

500

600

700

800

900

16B 32B 64B 128 256B 512B 1K 2K 4K 10M

Buffer Size

Tie

m (

s)

Otheretc. CPUSeekWriteRead

Breakdown – C

0

50

100

150

200

250

300

350

400

450

16B 32B 64B 128B 256B 512B 1K 2K 4K 10M

Buffer Size

Tim

e (s

)

idle

etc.CPU

seek

read

write

Test 3 Analysis

• Direct buffering improves I/O: ~50% reducing system calls slower than C/C++: ~300%

• Larger buffer? no big gain: Amdahl’s law!

• Does not help in random access low hit ratio: less than 1%

Test 4: Operation Size

• Test parameters:

buffer size : 0 Byte

• Sequential Write/Read

• Random Write/Read

Sequential Write/Read: 100M

0

100

200

300

400

500

600

700

800

0 2 4 6 8 10 12

Operation Size (2^x Bytes)

Ela

ps

e T

ime

(s

)

C

Java

Random Write/Read: 10M

0

50

100

150

200

250

0 2 4 6 8 10

Operation Size ( 2^x Byte)

Ela

ps

e T

ime

(s

)

C

Java

Test 4 Analysis

• Increasing operation size helps: ~ 85%reducing I/O system calls comparable to C/C++

• Large operation size

– no big gain.

• Random Access is similar

Test 5: Java JNI

• Test parameters:

file size : 100 MB

buffer size : 4 KB

• Sequential Write/Read

Java JNI Buffering

0

50

100

150

200

250

300

350

0 2 4 6 8 10

Operation Size (2^x Bytes)

Ela

pse

Tim

e (s

)

JNI

Direct Buffer

C

Breakdown – JNI buffering

0

50

100

150

200

250

300

1B 4B 16B 64B 256B 1K

Operation Size

Ela

pse

Tim

e (s

)

idle

etc.CPU

jniwrite

jniread

Test 5 Analysis

• I/O system calls are cheap (C/C++ level);• But, cost of calling native method is high;• Small operation size:

more native calls, comparable to Direct Buffering;

• Large operation size:less native calls,comparable to C/C++.

Conclusions

• Java raw I/O: 200%x slower than C• Buffering improves I/O

Reducing system calls220% improvement vs. no bufferBut, still 364%x slower than C

• Random I/O – no help with buffering? – locality of access;

Conclusions (continued)

• Increasing operation size helpsComparable to C/C++

• JNIsystem calls are cheap (C/C++ level);cost of calling native method is high;reduce native call times:

Comparable to C/C++

Thank You…