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Understanding
Memory Management of JavaVM
in 15 minutes
@stanaka / id:stanaka
JVM Operation Casual Talks at 2014/4/7
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Shinji TANAKA
CTO at Hatena Co., Ltd.
࠷ۙͷ׆ಈ: Immutable Infrastructure
@stanaka / id:stanaka
We’re Hiring at both
KYOTO and TOKYO!
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Java Virtual Machine
ʮͯͳʯͰಈ͍͍ͯΔ(͍ͨ)JavaVM
Hadoop
Solr
Elasticsearch
Scala ← new!
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powered by Scala
https://mackerel.io/
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JVMͷࠔΓͲ͜Ζ
ࡉ͔ͳνϡʔχϯά͕Ͱ͖Δ
ىಈ͕͍
σϑΥϧτ͕͍͚ͯͳ͍
ωοτ্ʹݹ͍ใ͕ଟ͍
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JVMͷࠔΓͲ͜Ζ
ࡉ͔ͳνϡʔχϯά͕Ͱ͖Δ
ىಈ͕͍
σϑΥϧτ͕͍͚ͯͳ͍
ωοτ্ʹݹ͍ใ͕ଟ͍
G1HeapRegionSizeͬͯͳʹ?
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JVMͷࠔΓͲ͜Ζ
ࡉ͔ͳνϡʔχϯά͕Ͱ͖Δ
ىಈ͕͍
σϑΥϧτ͕͍͚ͯͳ͍
ωοτ্ʹݹ͍ใ͕ଟ͍
͍͜ͳ͢ʹɺͪΌΜͱ͕ͨࣝ͠ඞཁ!!
G1HeapRegionSizeͬͯͳʹ?
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Memory Model in JavaVM
Stack ← ελοΫྖҬ
εϨου͝ͱʹ͋Δ
Non Heap ← JavaVM෦Ͱ͏ྖҬ
ίʔυΩϟογϡ (JIT݁ՌͳͲ)
Permanent Generation (Java8͔Βআ)
Heap ← ΞϓϦέʔγϣϯ͕͏ྖҬ
GCର
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Heap
Young Generation
Eden Space
Survivor Space (ෳ͋Δ)
Old / Tenured Generation
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Garbage Collection Algorithms
Mark & Sweep
Mark & Compaction
Generational GC (JDK 1.2, 1998)
Parallel GC
Incremental GC (-Xincgc, Java8Ͱඇਪ)
Concurrent Mark-Sweep GC, CMS (JDK 1.4.1 2002)
Garbage-First GC, G1 GC (JDK 1.6u14 2009)
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Minor-GC
from Memory Management in the Java HotSpot Virtual Machine [Whitepaper2006]
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Minor-GC
from Memory Management in the Java HotSpot Virtual Machine [Whitepaper2006]
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Parallel Collector
from Memory Management in the Java HotSpot Virtual Machine [Whitepaper2006]
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Concurrent GC (CMS)
from Memory Management in the Java HotSpot Virtual Machine [Whitepaper2006]
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Pros/Cons of CMS
Pros
Concurrent!
Stop-the-World͕͔͍࣌ؒ
Cons
Old Gen͕flagmentԽ(compaction͞Εͳ͍)͠
Old GenͰͷϝϞϦ֬อ͕͘ͳΔ
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CMS / G1
from The Garbage-First Garbage Collector [JavaOne2008]
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CMS vs G1
͞ΕͨYoungྖҬΛ࣋ͨͳ͍ (G1)
Heap͕ϦʔδϣϯͰׂ͞ΕΔ
ΦϒδΣΫτஔͷ࠷దԽ͕͞ΕΔ(G1)
SparseͳϦʔδϣϯ࠶ஔ͞ΕCompaction͞ΕΔ
Snapshot-at-the-beginingʹΑΔMarking(G1)
CMSͰDirty-card
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GC Benchmark
Parallel CMS G1
Total GC
pauses
20,930ms 18,870ms 62,000ms
Max GC pause 721ms 64ms 50ms
JIRA benchmark test for 30 minutes
with -Xms256m -Xmx768m -XX:MaxPermSize=256m
https://plumbr.eu/blog/g1-vs-cms-vs-parallel-gc
Tuning͢ΔͱG1ͷ΄͏͕CPUෛՙ
ؚΊͯྑ͍ͱ͍͏݁Ռ͋Δ [JavaOne2013]
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ͲͷGCΛ͏͖?
ϫʔΫϩʔυͱαʔόʔεϖοΫ࣍ୈ
ώʔϓαΠζ (ඦMBʙेGBʙTB)
ΦϒδΣΫτੜɺαΠζɺण໋ͷ
CPUޮͱϨΠςϯγͱνϡʔχϯάͷखؒ
τϨʔυΦϑ
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Reference
Memory Management in the Java HotSpot Virtual Machine
ˑ http://www.oracle.com/technetwork/java/javase/memorymanagement-whitepaper-150215.pdf
[Whitepaper2006]
A Generational Mostly-concurrent Garbage Collector
https://www.cs.purdue.edu/homes/hosking/ismm2000/papers/printezis.pdf [ISMM2000]
The Garbage-First Garbage Collector
http://www.oracle.com/technetwork/java/javase/tech/g1-intro-jsp-135488.html
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.63.6386&rep=rep1&type=pdf [ISMM2004]
ˑ http://www.oracle.com/technetwork/server-storage/ts-5419-159484.pdf [JavaOne 2008]
Garbage-First Garbage Collector: Migration to, Expectations and Advanced Tuning.
ˑ http://www.slideshare.net/MonicaBeckwith/garbage-first-garbage-collector-g1-gc-migration-to-
expectations-and-advanced-tuning [JavaOne2013]
Java Virtual Machine Technology
http://docs.oracle.com/javase/8/docs/technotes/guides/vm/
International Symposium on Memory Management (ISMM)
http://www.sigplan.org/conferences/ismm/main