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JVM Tuning in a rush Tomasz Borek, Symentis

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• Infected in childhood • From me parents • Amstrad, ElWro Junior • Games! Doh! • Mem pages in DOS anyone? • In IT • ETL, crawlers, web-app, archi • IAAS, SAAS, own servers • Java 4 – 7, GNU/Linux, SQLs • Ardent “activist” Tomasz Borek

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Can be found in the net! :P https://lafkblogs.wordpress.com/ https://twitter.com/lafk_pl https://pl.linkedin.com/in/tjborek GeeCON, ChamberConf, Confitura, Lambda Days, LambdaCon, Java Developer Days, JavaDay Lviv, JavaDay Kiev

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Tomek in IT groups .com http://java.pl Kraków Poznań Praga Sopot http://geecon.org

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Prod hits rock bottom ● Everybody is kung-fu fighting ● Must be quick like lightning

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So! Being a dev, you need: 1.To know your traffic and your app and your infra

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So! Being a dev, you need: 1.To know your traffic and your app and your infra 2.To know recent changes

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So! Being a dev, you need: 1.To know your traffic and your app and your infra 2.To know recent changes 3.To know your limits (sometimes comes from point 1)

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So! Being a dev, you need: 1.To know your traffic and your app and your infra 2.To know recent changes 3.To know your limits (sometimes comes from point 1) 4.To have access to monitoring

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So! Being a dev, you need: 1.To know your traffic and your app and your infra 2.To know recent changes 3.To know your limits (sometimes comes from point 1) 4.To have access to monitoring 5.To adjust pooling (both thread and connection)

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So! Being a dev, you need: 1.To know your traffic and your app and your infra 2.To know recent changes 3.To know your limits (sometimes comes from point 1) 4.To have access to monitoring 5.To adjust pooling (both thread and connection) 6.To peruse logs and pull out anomalies

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So! Being a dev, you need: 1.To know your traffic and your app and your infra 2.To know recent changes 3.To know your limits (sometimes comes from point 1) 4.To have access to monitoring 5.To adjust pooling (both thread and connection) 6.To peruse logs and pull out anomalies 7.TO TUNE JVM

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So! Being a dev, you need: 1.To know your traffic and your app and your infra 2.To know recent changes 3.To know your limits (sometimes comes from point 1) 4.To have access to monitoring 5.To adjust pooling (both thread and connection) 6.To peruse logs and pull out anomalies 7.TO TUNE JVM

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JVM? Meaning? • Sun Hotspot • IBM • JRockit • IceTea • OpenJDK • TCK decides

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JVM? Meaning? • Sun Hotspot • IBM • JRockit • IceTea • OpenJDK • TCK decides

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JVM? Meaning? • Sun Hotspot – but which version? • IBM • JRockit • IceTea • OpenJDK • TCK decides

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JVM? Meaning? • Sun Hotspot – but which version? And architecture? • IBM • JRockit • IceTea • OpenJDK • TCK decides

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So! JVM tuning? 1.To adjust GC, based on it's logs

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So! JVM tuning? 1.To adjust GC, based on it's logs 2.To adjust (native) heap

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So! JVM tuning? 1.To adjust GC, based on it's logs 2.To adjust (native) heap 3.Tweaking JVM starting flags

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So! JVM tuning? 1.To adjust GC, based on it's logs 2.To adjust (native) heap 3.Tweaking JVM starting flags 4.To use TOOLS

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Today! ● JVM tuning ● Diagnosing performance problems ● Tools ● All in a rush

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JVM tuning

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Takeaway #1 JVM is a process

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Being a process means ● OS architecture enforces JVM architecture ● Your memory is limited by OS and other processes – Heap is one – C-heap is another! ● IO-wise and thread-wise: – Your threads and files opened are limited by ulimit ● File descriptors!

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OOM flavours?

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OOM flavours ● Out of HeapSpace

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OOM flavours ● Out of HeapSpace ● PermGen error

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OOM flavours ● Out of HeapSpace ● PermGen error ● Unable to create native thread

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OOM flavours ● Out of HeapSpace ● PermGen error ● Unable to create native thread ● There are others, these are most popular

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API says OutOfMemoryError is ● Thrown when the Java Virtual Machine cannot allocate an object because it is out of memory, and no more memory could be made available by the garbage collector. OutOfMemoryError objects may be constructed by the virtual machine as if suppression were disabled and/or the stack trace was not writable.

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API says OutOfMemoryError is ● Thrown when the Java Virtual Machine cannot allocate an object because it is out of memory, and no more memory could be made available by the garbage collector. OutOfMemoryError objects may be constructed by the virtual machine as if suppression were disabled and/or the stack trace was not writable.

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API says OutOfMemoryError is ● Due to failure in allocating an object after garbage collection. ● Nothing about threads. ● Nothing about PermGen.

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How much memory JVM uses? ● Say you start it with Xmx == Xms == 1GB

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How much memory JVM uses? ● Say you start it with Xmx == Xms == 1GB ● 1GB?

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How much memory JVM uses? ● Say you start it with Xmx == Xms == 1GB ● 1GB? ● Around 1GB?

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How much memory JVM uses? ● Say you start it with Xmx == Xms == 1GB ● 1GB? ● Around 1GB? ● If we talk about Java HEAP

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Memory management Entire RAM ● 32 bits: can address less than 4GB. ● 64 bits: can address… theoretically 16 EB. – Still – much more! ● There's much more to 32vs64 but that's for another time

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Memory management Entire RAM What's left of RAM – C-HEAP JVM heap -Xmx ● -Xms – minimal heap size ● -Xmx – maximal heap size ● When both should be set to same value?

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Memory management Entire RAM What's left of RAM – C-HEAP JVM heap What's left – C-HEAP JVM ops JVM heap -Xmx PermGen

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PermGen ● Permanent Generation – Early Java – for JDK classes – and Strings ● Back then – good idea ● Now removed – JDK 7 – Strings no longer in PermGen – JDK 8 – no PermGen at all

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PermGen ● Permanent Generation – Early Java – for JDK classes – and Strings ● Back then – good idea ● Now removed – JDK 7 – Strings no longer in PermGen – JDK 8 – no PermGen at all Quick fix? Increase PermGen size.

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Memory management What's left – C-HEAP JVM ops JVM heap -Xmx PermGen

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GC ● When it runs?

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GC ● When it runs? ● Minor collection?

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GC ● When it runs? ● Minor collection? ● Major collection?

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GC ● When it runs? ● Minor collection? ● Major collection? ● How can a dev tune GC?

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Generational GC Tenured – where long-lived are promoted Eden – infants that die quickly ● Studies showed: – most objects die young – Some live really long ● Ergo: short- and long-lived division ● Minor collection: Eden ● Major collection: whole heap

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Generational GC - mechanics ● In fact Eden has also 2 Survivor spaces – To handle locality – Helps compress after freeing space – First promotion to survivor, then to tenured ● Flags tell: – How many GCs object must survive to be promoted – How large Eden / Tenured / Survivors spaces are – What is logged (how details GC logs are) – Many, MANY more

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Memory management trade-offs ● Large heap – large full GC – small native and C-heap? ● Smaller heap – minor GC may be enough ● Make sure your objects die young and only really long lived reach tenured

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JVM tuning 1.To adjust GC, based on it's logs 2.To adjust (native) heap 3.Tweaking JVM starting flags 4.To use TOOLS – later

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Takeaway #2 Log GC

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Takeaway #3 GC tuning is a trade-off

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Diagnosing performance problems

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„The Box” • Heinz Kabutz, Kirk Pepperdine • Top - bottom

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„The Box” • TRAFFIC: ? TRAFFIC

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„The Box” • TRAFFIC: how is app used? TRAFFIC: people, automatic

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„The Box” • TRAFFIC: how is app used? • CODE: ? TRAFFIC: people, automatic Application CODE

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„The Box” • TRAFFIC: how is app used? • CODE: threads, algos, data structures... TRAFFIC: people, automatic CODE: threads, data structs, algo

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„The Box” • TRAFFIC: how is app used? • CODE: threads, algos, data structures... • JVM: ? TRAFFIC: people, automatic CODE: threads, data structs, algo JVM

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„The Box” • TRAFFIC: how is app used? • CODE: threads, algos, data structures... • JVM: ? TRAFFIC: people, automatic CODE: threads, data structs, algo JVM: flags, GC

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„The Box” • TRAFFIC: how is app used? • CODE: threads, algos, data structures... • JVM: starting flags, GC • OS: ? TRAFFIC: people, automatic CODE: threads, data structs, algo JVM: flags, GC OS

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„The Box” • TRAFFIC: how is app used? • CODE: threads, algos, data structures... • JVM: starting flags, GC • OS: ulimit, FS, config, archi, other procs… TRAFFIC: people, automatic CODE: threads, data structs, algo JVM: flags, GC OS: FS, config, limits

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„The Box” • TRAFFIC: how is app used? • CODE: threads, algos, data structures... • JVM: starting flags, GC • OS: ulimit, FS, config, archi, other procs… • VIRT: ? TRAFFIC: people, automatic CODE: threads, data structs, algo JVM: flags, GC OS: FS, config, limits VIRT

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„The Box” • TRAFFIC: how is app used? • CODE: threads, algos, data structures... • JVM: starting flags, GC • OS: ulimit, FS, config, archi, other procs… • VIRT: hell depends! TRAFFIC: people, automatic CODE: threads, data structs, algo JVM: flags, GC OS: FS, config, limits VIRT

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„The Box” • TRAFFIC: how is app used? • CODE: threads, algos, data structures... • JVM: starting flags, GC • OS: ulimit, FS, config, archi, other procs… • VIRT: hell depends! • HARDWARE: ? TRAFFIC: people, automatic CODE: threads, data structs, algo JVM: flags, GC OS: FS, config, limits VIRT HARDWARE

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„The Box” • TRAFFIC: how is app used? • CODE: threads, algos, data structures... • JVM: starting flags, GC • OS: ulimit, FS, config, archi, other procs… • VIRT: hell depends! • HARDWARE: 32 vs 64, RAM, BIOS, drivers… TRAFFIC: people, automatic CODE: threads, data structs, algo JVM: flags, GC OS: FS, config, limits VIRT HARDWARE

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Brendan Gregg – USE • Utilization, Saturation, Errors • Use – how much in use is your resource • Saturation – how many requests await (waiting queue) • Errors – what errors are thrown by resource • http://www.brendangregg.com/usemethod.html • Create a checklist for each important resource, for finding out Utilization, Saturation and Errors and you'll know how to soon find out what is going on with resource

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Takeaway #1 The Box

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Takeaway #2 GNU/Linux perf? Brendan Gregg

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TOOLS

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Takeaway #1 GNU/Linux surely has a tool for that

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How to find your java process? ● ps … | grep java ●

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How to find your java process? ● ps … | grep java ● pgrep java

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How to find your java process? ● ps … | grep java ● pgrep java ● jps

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How to change flags on-the-fly? ● jinfo

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How to dump threads or heap? ● kill -3

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How to dump threads or heap? ● kill -3 ● jstack

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How to dump threads or heap? ● kill -3 ● jstack ● jhat (heap)

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jvisualvm ● Deserves it's own slide ● Profiler, sampler ● Monitor (heap, threads, etc.) ● Calls GC, does dumps

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SUMMARIZING ● For being rushed – prepare in advance – Monitoring, logs, ceilings, etc. ● Log GC ● JVM is a process – all process limits in your OS apply ● The Box ● Brendan Gregg ● GNU/Linux – tools unparalleled

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