An InDepth Examination of Java IO Performance and Possible Tuning Strategies

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An In-Depth Examination of Java I/O Performance
and Possible Tuning Strategies

• Kai Xu xuk_at_cs.wisc.edu
• Hongfei Guo guo_at_cs.wisc.edu

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Outline

• Why bother? (Problems)
• Our goals
• Java I/O overview
• Tests design
• Test results and analysis
• Conclusions

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Why bother?

• Growing interest in using Java
• Much works had been done in Java performance
  evaluation but
• NOT in Java I/O

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Our Goals

• Is it really bad (Compared with C/C)
• How bad
• Possible tuning strategies
• How well they work

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An Overview of Java I/O Classes
Random AccessFile
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Test Design

• Access patterns
• Sequential write/read
• Random write/read
• Data interested
• Elapse time, CPU breakdown
• Comparison group C/C

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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

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Test Setup

• Hardware configuration
• CPU Pentium III 667 MHz
• Memory 128 MB
• Disk 10 GB IDE
• Software configuration
• OS Redhat 6.2
• JVM JDK 1.2.2
• Profiling Tools
• PerfAnal profiler, gprof profiler
  2.9.5, time

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Test 1 The lowest level Java I/O

• Test parameters
• buffer size 0 Byte
• operation size 1 Byte
• Sequential Write/Read
• Random Write/Read

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Sequential Write/Read
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Breakdown -- File size 100M
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Random Write/Read
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Breakdown -- File size 10M
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Test 1 Analysis

• Java raw I/O 200x slower
• Java system calls cost more
• read 224x
• write 158x
• Random Access is similar

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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

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Buffering Strategies in Java
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CPU Breakdown
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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

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Test 3 Direct Buffering

• Test parameters
• file size 100 MB
• operation size 1 Byte
• Sequential Write/Read
• Random Write/Read

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Sequential Write/Read
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Breakdown Java
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Breakdown C
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Random Write/Read
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Breakdown Java
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Breakdown C
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Test 3 Analysis

• Direct buffering improves I/O 50
• reducing system calls
• slower than C/C 300
• Larger buffer? no big gain Amdahls law!
• Does not help in random access
• low hit ratio less than 1

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Test 4 Operation Size

• Test parameters
• buffer size 0 Byte
• Sequential Write/Read
• Random Write/Read

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Sequential Write/Read 100M
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Random Write/Read 10M
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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

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Test 5 Java JNI

• Test parameters
• file size 100 MB
• buffer size 4 KB
• Sequential Write/Read

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Java JNI Buffering
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Breakdown JNI buffering
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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.

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Conclusions

• Java raw I/O 200x slower than C
• Buffering improves I/O
• Reducing system calls
• 220 improvement vs. no buffer
• But, still 364x slower than C
• Random I/O no help with buffering?
• locality of access

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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

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Thank You