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An In-Depth Examination of Java
I/O Performance
and
Possible Tuning Strategies
Kai Xu
[email protected]
Hongfei Guo [email protected]
Outline
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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
•
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Is it really bad (Compared with C/C++)
How bad
Possible tuning strategies
How well they work
An Overview of Java I/O Classes
OutputStream
Random
AccessFile
InputStream
FileOutputStream
FileInputStream
ByteArrayOutputStream
ByteArrayInputStream
FilterOutputStream
FilterInputStream
BufferedOutputStream
BufferedInputStream
DataOutputStream
DataInputStream
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 configuration
CPU:
Memory:
Disk:
Pentium III 667 MHz
128 MB
10 GB IDE
• Software configuration
OS :
JVM :
Redhat 6.2
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
800
Elapse Time (s)
700
600
500
C
400
Java
300
200
100
0
0
10
20
30
40
50
60
File Size (M)
70
80
90
100
Breakdown -- File size: 100M
400
350
Time (s)
300
250
C
Java
200
150
100
50
0
read
write
etc.cpu
other
Random Write/Read
250
Elapse Time (s)
200
150
C
Java
100
50
0
1
2
3
4
5
6
File Size (M)
7
8
9
10
Breakdown -- File size: 10M
70
60
Time (s)
50
40
C
Java
30
20
10
0
read
write
seek
other cpu
waiting
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
800
700
600
500
No Buffer
Buffered Stream
Direct Buffer
400
300
200
100
0
Total
Seq Write
Seq Read
CPU Breakdown
160
140
100
80
60
40
20
arraycopy
write
read
buffer.write
0
buffer.read
Time (s)
120
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
800
700
Elapse Time ( s )
600
500
C
400
Java
300
200
100
0
0
2
4
6
8
Buffer Size (2^x Bytes)
10
12
Breakdown – Java
500
450
400
Time (s)
350
other
etc. CPU
memcpy
read
write
300
250
200
150
100
50
0
16B
32B
64B 128B 256B 512B
1K
Buffer Size
2K
4K
1M
10M
Breakdown – C
120
100
wait
Buffer Size
80
etc. CPU
memcpy
60
read
write
40
20
0
16B
32B
64B 128B 256B 512B
1K
2K
4K
1M
10M
Random Write/Read
900
800
Elapse Time (s)
700
600
500
C
Java
400
300
200
100
0
0
2
4
6
8
Buffer Size (2^x Bytes)
10
12
Breakdown – Java
900
800
700
Other
etc. CPU
Seek
Write
Read
Tiem (s)
600
500
400
300
200
100
0
16B
32B
64B
128 256B 512B
Buffer Size
1K
2K
4K
10M
Breakdown – C
450
400
350
idle
etc.CPU
seek
read
write
Time (s)
300
250
200
150
100
50
0
16B 32B 64B 128B 256B 512B 1K
Buffer Size
2K
4K 10M
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
800
Elapse Time (s)
700
600
500
C
Java
400
300
200
100
0
0
2
4
6
8
Operation Size (2^x Bytes)
10
12
Random Write/Read: 10M
250
Elapse Time (s)
200
150
C
Java
100
50
0
0
2
4
6
Operation Size ( 2^x Byte)
8
10
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
350
Elapse Time (s)
300
250
JNI
200
Direct Buffer
150
C
100
50
0
0
2
4
6
8
Operation Size (2^x Bytes)
10
Breakdown – JNI buffering
300
Elapse Time (s)
250
200
idle
etc.CPU
jniwrite
jniread
150
100
50
0
1B
4B
16B
64B
Operation Size
256B
1K
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 calls
220% improvement vs. no buffer
But, still 364%x slower than C
• Random I/O – no help with buffering?
– locality of access;
Conclusions (continued)
• Increasing operation size helps
Comparable to C/C++
• JNI
system calls are cheap (C/C++ level);
cost of calling native method is high;
reduce native call times:
Comparable to C/C++
Thank You…