java tuning on gnu/linux for busy dev
TRANSCRIPT
Wprowadzenie do strojenia Javy na
GNU/Linux dla zajętego programisty
Tomasz Borek, Symentis
• 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
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
Tomek in IT groups
.com
http://java.pl KrakówPoznańPragaSopot
http://geecon.org
Prod hits rock bottom● Everybody is kung-fu fighting● Must be quick like lightning
So! Being a dev, you need:
1.To know your traffic and your app and your infra
So! Being a dev, you need:
1.To know your traffic and your app and your infra2.To know recent changes
So! Being a dev, you need:
1.To know your traffic and your app and your infra2.To know recent changes3.To know your limits (sometimes comes from point 1)
So! Being a dev, you need:
1.To know your traffic and your app and your infra2.To know recent changes3.To know your limits (sometimes comes from point 1)4.To have access to monitoring
So! Being a dev, you need:
1.To know your traffic and your app and your infra2.To know recent changes3.To know your limits (sometimes comes from point 1)4.To have access to monitoring5.To adjust pooling (both thread and connection)
So! Being a dev, you need:
1.To know your traffic and your app and your infra2.To know recent changes3.To know your limits (sometimes comes from point 1)4.To have access to monitoring5.To adjust pooling (both thread and connection)6.To peruse logs and pull out anomalies
So! Being a dev, you need:
1.To know your traffic and your app and your infra2.To know recent changes3.To know your limits (sometimes comes from point 1)4.To have access to monitoring5.To adjust pooling (both thread and connection)6.To peruse logs and pull out anomalies7.TO TUNE JVM
So! Being a dev, you need:
1.To know your traffic and your app and your infra2.To know recent changes3.To know your limits (sometimes comes from point 1)4.To have access to monitoring5.To adjust pooling (both thread and connection)6.To peruse logs and pull out anomalies7.TO TUNE JVM
JVM? Meaning?
• Sun Hotspot• IBM• JRockit• IceTea• OpenJDK• TCK decides
JVM? Meaning?
• Sun Hotspot• IBM• JRockit• IceTea• OpenJDK• TCK decides
JVM? Meaning?
• Sun Hotspot – but which version?• IBM• JRockit• IceTea• OpenJDK• TCK decides
JVM? Meaning?
• Sun Hotspot – but which version? And architecture?• IBM• JRockit• IceTea• OpenJDK• TCK decides
So! JVM tuning?
1.To adjust GC, based on it's logs
So! JVM tuning?
1.To adjust GC, based on it's logs2.To adjust (native) heap
So! JVM tuning?
1.To adjust GC, based on it's logs2.To adjust (native) heap 3.Tweaking JVM starting flags
So! JVM tuning?
1.To adjust GC, based on it's logs2.To adjust (native) heap 3.Tweaking JVM starting flags4.To use TOOLS
Today!● JVM tuning ● Diagnosing performance problems ● Tools● All in a rush
JVM tuning
Takeaway #1
JVM is a process
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!
OOM flavours?
OOM flavours● Out of HeapSpace
OOM flavours● Out of HeapSpace● PermGen error
OOM flavours● Out of HeapSpace● PermGen error● Unable to create native thread
OOM flavours● Out of HeapSpace● PermGen error● Unable to create native thread● There are others, these are most popular
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.
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.
API says OutOfMemoryError is● Due to failure in allocating an object after garbage
collection.● Nothing about threads.● Nothing about PermGen.
How much memory JVM uses?● Say you start it with Xmx == Xms == 1GB
How much memory JVM uses?● Say you start it with Xmx == Xms == 1GB● 1GB?
How much memory JVM uses?● Say you start it with Xmx == Xms == 1GB● 1GB?● Around 1GB?
How much memory JVM uses?● Say you start it with Xmx == Xms == 1GB● 1GB?● Around 1GB?● If we talk about Java HEAP
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
Memory management
Entire RAM
What's left of RAM – C-HEAPJVM heap
-Xmx
● -Xms – minimal heap size● -Xmx – maximal heap size● When both should be set to same value?
Memory management
Entire RAM
What's left of RAM – C-HEAPJVM heap
What's left – C-HEAPJVM opsJVM heap
-Xmx
PermGen
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
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.
Memory management
What's left – C-HEAPJVM opsJVM heap
-Xmx
PermGen
GC● When it runs?
GC● When it runs?● Minor collection?
GC● When it runs?● Minor collection?● Major collection?
GC● When it runs?● Minor collection?● Major collection?● How can a dev tune GC?
Generational GC
Tenured – where long-lived are promotedEden – 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
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
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
JVM tuning
1.To adjust GC, based on it's logs2.To adjust (native) heap 3.Tweaking JVM starting flags4.To use TOOLS – later
Takeaway #2
Log GC
Takeaway #3
GC tuning is a trade-off
Diagnosing performance problems
„The Box”
• Heinz Kabutz, Kirk Pepperdine• Top - bottom
„The Box”
• TRAFFIC: ?TRAFFIC
„The Box”
• TRAFFIC: how is app used? TRAFFIC: people, automatic
„The Box”
• TRAFFIC: how is app used?• CODE: ?
TRAFFIC: people, automatic
Application CODE
„The Box”
• TRAFFIC: how is app used?• CODE: threads, algos, data structures...
TRAFFIC: people, automatic
CODE: threads, data structs, algo
„The Box”
• TRAFFIC: how is app used?• CODE: threads, algos, data structures...• JVM: ?
TRAFFIC: people, automatic
CODE: threads, data structs, algo
JVM
„The Box”
• TRAFFIC: how is app used?• CODE: threads, algos, data structures...• JVM: ?
TRAFFIC: people, automatic
CODE: threads, data structs, algo
JVM: flags, GC
„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
„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
„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
„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
„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
„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
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
Takeaway #1
The Box
Takeaway #2
GNU/Linux perf? Brendan Gregg
TOOLS
Takeaway #1
GNU/Linux surely has a tool for that
How to find your java process?● ps … | grep java●
How to find your java process?● ps … | grep java● pgrep java
How to find your java process?● ps … | grep java● pgrep java● jps
How to change flags on-the-fly?● jinfo
How to dump threads or heap?● kill -3
How to dump threads or heap?● kill -3● jstack
How to dump threads or heap?● kill -3● jstack● jhat (heap)
jvisualvm● Deserves it's own slide● Profiler, sampler● Monitor (heap, threads, etc.)● Calls GC, does dumps
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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