Enabling Java in Latency Sensitive Environments

Enabling Java
in
Latency Sensitive
Applications
Gil Tene, CTO & co-Founder, Azul Systems
©2013 Azul Systems, Inc.

Watch the video with slide
synchronization on InfoQ.com!
http://www.infoq.com/presentations
/java-tuning-latency

InfoQ.com: News & Community Site
• 750,000 unique visitors/month
• Published in 4 languages (English, Chinese, Japanese and Brazilian
Portuguese)
• Post content from our QCon conferences
• News 15-20 / week
• Articles 3-4 / week
• Presentations (videos) 12-15 / week
• Interviews 2-3 / week
• Books 1 / month

Presented at QCon San Francisco
www.qconsf.com
Purpose of QCon
- to empower software development by facilitating the spread of
knowledge and innovation
Strategy
- practitioner-driven conference designed for YOU: influencers of
change and innovation in your teams
- speakers and topics driving the evolution and innovation
- connecting and catalyzing the influencers and innovators
Highlights
- attended by more than 12,000 delegates since 2007
- held in 9 cities worldwide

High level agenda
Low Latency?

In Java?

Seriously?

The problem with . . .

What happens when you solve that problem?

The next problems

A bit of shameless bragging

About me: Gil Tene
co-founder, CTO @Azul
Systems

Have been working on “think
different” GC approaches
since 2002

Created Pauseless & C4 core
GC algorithms (Tene, Wolf)

A Long history building
Virtual & Physical Machines,
Operating Systems,
Enterprise apps, etc...

JCP EC Member...

* working on real-world trash compaction issues, circa 2004

About Azul
We make scalable Virtual
Machines

Vega

Have built “whatever it takes to
get job done” since 2002

3 generations of custom SMP
Multi-core HW (Vega)

Zing: Pure software for
commodity x86

Known for Low Latency,
Consistent execution, and Large
data set excellence


C4

Java in the low latency world?


Java in the low latency world?
Why do people use Java for low latency apps?

Are they crazy?

No. There are good, easy to articulate reasons

Projected lifetime cost

Developer productivity

Time-to-product, Time-to-market, ...

Leverage, ecosystem, ability to hire

E.g. Customer answer to:
“Why do you use Java in Algo Trading?”
Strategies have a shelf life

We have to keep developing and deploying new ones

Only one out of N is actually productive

Proﬁtability therefore depends on ability to
successfully deploy new strategies, and on the cost
of doing so

Our developers seem to be able to produce 2x-3x as
much when using a Java environment as they would
with C/C++ ...

So what is the problem?
Is Java Slow?
No

A good programmer will get roughly the same speed
from both Java and C++

A bad programmer won’t get you fast code on either

The 50%‘ile and 90%‘ile are typically excellent...

It’s those pesky occasional stutters and stammers
and stalls that are the problem...

Ever hear of Garbage Collection?

Is “jitter” even the right word for this?
Hiccups&by&Time&Interval&
Max"per"Interval"

99%"

99.90%"

99.99%"

Max"

Hiccup&Dura*on&(msec)&

25"
20"
15"
10"
5"
0"
0"

100"

200"

300"

400"

500"

&Elapsed&Time&(sec)&

99%‘ile is

25"

Max is ~30,000%
Hiccups&by&Percen*le&Distribu*on&
~60 usec

higher than “typical”

600"

Stop-The-World Garbage Collection:
Java’s Achilles heel
Let’s ignore the bad multi-second pauses for now...

Low latency applications regularly experience “small”,
“minor” GC events that range in the 10s of msec

Frequency directly related to allocation rate

So we have great 50%, 90%. Maybe even 99%

But 99.9%, 99.99%, Max, all “suck”

So bad that it affects risk, proﬁtability, service
expectations, etc.

One way to deal with Stop-The-World GC


A common way to “deal” with STW-GC
Averages and Standard Deviation


Reality: Latency is usually
strongly “multi-modal”
Usually does’t look anything like a normal
distribution

In software systems, usually shows periodic freezes

Complete shifts from one mode/behavior to another

Mode A: “good”.

Mode B: “Somewhat bad”

Mode C: “terrible”, ...

....
©2012

Another way to cope: “Creative Language”
“Guarantee a worst case of 5 msec, 99% of the time”

“Mostly” Concurrent, “Mostly” Incremental

Translation: “Will at times exhibit long monolithic stopthe-world pauses”

“Fairly Consistent”

Translation: “Will sometimes show results well outside
this range”

“Typical pauses in the tens of milliseconds”

Translation: “Some pauses are much longer than tens of
milliseconds”

Another way to deal with STW-GC


What do actual low latency developers
do about it?
They use “Java” instead of Java

They write “in the Java syntax”

They avoid allocation as much as possible

E.g. They build their own object pools for everything

They write all the code they use (no 3rd party libs)

They train developers for their local discipline

In short: They revert to many of the practices that
hurt productivity. They loose out on much of Java.

was**
It is an industry-wide problem
Stop-The-World GC mechanisms
contradict the fundamental
requirements of
low latency & low jitter apps

(** It’s 2013... We now have Zing.)

The common GC behavior across ALL
currently shipping (non-Zing) JVMs
ALL use a Monolithic Stop-the-world NewGen

“small” periodic pauses (small as in 10s of msec)

pauses more frequent with higher throughput or allocation rates

Development focus for ALL is on Oldgen collectors

Focus is on trying to address the many-second pause problem

Usually by sweeping it farther and farther the rug

“Mostly X” (e.g. “mostly concurrent”) hides the fact that they
refer only to the OldGen part of the collector

E.g. CMS, G1, Balanced.... all are OldGen-only efforts

ALL use a Fallback to Full Stop-the-world Collection

Used to recover when other mechanisms (inevitably) fail

Also hidden under the term “Mostly”...

A Recipe: address STW-GC head-on
E.g. at Azul, we decided to focus on the core problems

Scale & productivity limited by responsiveness/latency

And it’s not the “typical” latency, it’s the outliers...

Even “short” GC pauses must be considered a problem

Responsiveness must be unlinked from key metrics:

Transaction Rate, Concurrent users, Data set size, etc.

Heap size, Live Set size, Allocation rate, Mutation rate

Responsiveness must be continually sustainable

Can’t ignore “rare but periodic” events

Eliminate ALL Stop-The-World Fallbacks

Any STW fallback is a real-world failure

Existence proof: The Zing “C4” Collector  
Continuously Concurrent Compacting Collector

Concurrent, compacting old generation

!

Concurrent, compacting new generation

!

No stop-the-world fallback

Always compacts, and always does so concurrently


Benefits


An example of “First day’s run” behavior
E-Commerce application

5 msec


An example of behavior after 4 days of system tuning
Low latency application

1 msec


Measuring Theory in Practice

jHiccup:

A tool that measures and reports

(as your application is running)

if your JVM is actually running

all the time

Discontinuities in Java platform execution - Easy To Measure
Incontinuities in Java platform execution
Hiccups"by"Time"Interval"

Max"per"Interval"

99%"

99.90%"

99.99%"

Max"


1800"

I call
these
“hiccups”

1600"
1400"
1200"
1000"
800"
600"
400"
200"
0"
0"

200"

400"

600"

800"

1000"

1200"

1400"

1600"

1800"


Hiccups"by"Percen@le"Distribu@on"

1800"


1600"

Max=1665.024&

1400"
1200"
1000"
800"
600"
400"
200"
0"


0%"

90%"

99%"

&
99.9%"

&
Percen*le&

99.99%"

99.999%"

A telco
App with
a bit of a
“problem”

Fun with jHiccup


Oracle HotSpot (pure newgen)

Zing

Max"per"Interval"

99%"

99.90%"

99.99%"

Max"per"Interval"

Max"

20"
15"
10"
5"
0"

99.99%"

Max"

1.6"
1.4"
1.2"
1"
0.8"
0.6"
0.4"
0.2"
0"

0"

100"

200"

300"

400"

500"

600"

0"

100"

200"


300"

400"

500"

600"



1.8"

25"

Max=22.656&

20"



99.90%"

1.8"



25"

99%"

15"
10"
5"

1.6"

Max=1.568&

1.4"
1.2"
1"
0.8"
0.6"
0.4"
0.2"

0"

0%"

90%"

&

99%"

99.9%"

&
99.99%"

99.999%"

Percen*le&

0"

0%"

90%"

&

99%"

Low latency trading application

99.9%"

&
99.99%"
Percen*le&

99.999%"

Oracle HotSpot (pure newgen)

Zing

Max"per"Interval"

99%"

99.90%"


99.99%"

Max"

Max"per"Interval"

20"
15"
10"
5"
0"
0"

Max"

100"

200"

300"

400"

500"

15"
10"
5"
0"

600"

0"

100"

200"

300"

400"

500"

600"




25"

25"

Max=22.656&

20"



99.99%"

20"


15"
10"
5"
0"

99.90%"

25"



25"

99%"

0%"

90%"

&

99%"

99.9%"

&
99.99%"

99.999%"

Percen*le&

20"
15"
10"
5"
0"

Max=1.568&
0%"

90%"

&

99%"

Low latency - Drawn to scale

99.9%"

&
99.99%"
Percen*le&

99.999%"

Takeaway: In 2013, “Real” Java is finally
viable for low latency applications
GC is no longer a dominant issue, even for outliers

2-3msec worst observed case with “easy” tuning

< 1 msec worst observed case is very doable

No need to code in special ways any more

You can finally use “real” Java for everything

You can finally 3rd party libraries without worries

You can finally use as much memory as you want

You can finally use regular (good) programmers

Lets not forget about GC tuning


Java GC tuning is “hard”…
Examples of actual command line GC tuning parameters:

Java -Xmx12g -XX:MaxPermSize=64M -XX:PermSize=32M -XX:MaxNewSize=2g

-XX:NewSize=1g -XX:SurvivorRatio=128 -XX:+UseParNewGC

-XX:+UseConcMarkSweepGC -XX:MaxTenuringThreshold=0

-XX:CMSInitiatingOccupancyFraction=60 -XX:+CMSParallelRemarkEnabled

-XX:+UseCMSInitiatingOccupancyOnly -XX:ParallelGCThreads=12

-XX:LargePageSizeInBytes=256m …

Java –Xms8g –Xmx8g –Xmn2g -XX:PermSize=64M -XX:MaxPermSize=256M

-XX:-OmitStackTraceInFastThrow -XX:SurvivorRatio=2 -XX:-UseAdaptiveSizePolicy

-XX:+UseConcMarkSweepGC -XX:+CMSConcurrentMTEnabled

-XX:+CMSParallelRemarkEnabled -XX:+CMSParallelSurvivorRemarkEnabled

-XX:CMSMaxAbortablePrecleanTime=10000 -XX:+UseCMSInitiatingOccupancyOnly

-XX:CMSInitiatingOccupancyFraction=63 -XX:+UseParNewGC –Xnoclassgc …

A
few
GC
tuning
ﬂags

Source:
Word
Cloud
created
by
Frank
Pavageau
in
his
Devoxx
FR
2012
presentaFon
Ftled
“Death
by
Pauses”

The complete guide to
modern GC tuning**

java -Xmx40g

(** It’s 2013... We now have Zing.)

So what’s next?
GC is only the biggest problem...


JVMs make many tradeoffs
often trading speed vs. outliers
Some speed techniques come at extreme outlier costs

E.g. (“regular”) biased locking

E.g. counted loops optimizations

Deoptimization

Lock deﬂation

Weak References, Soft References, Finalizers

Time To Safe Point (TTSP)

Time To Safepoint (TTSP)
Your new #1 enemy
(Once GC itself was taken care of)

Many things in a JVM (still) use a global safepoint

All threads brought to a halt, at a “safe to analyze”
point in code, and then released after work is done.

E.g. GC phase shifts, Deoptimization, Class Unloading,
Thread Dumps, Lock Deﬂation, Deadlock Detection, etc.

A single thread with a long time-to-safepoint path can
cause an effective pause for all other threads

Many code paths in the JVM are long...

Time To Safepoint (TTSP)
the most common examples
Array copies and object clone()

Counted loops

Many other other variants in the runtime...

Measure, Measure, Measure...

Zing has a built-in TTSP proﬁler

At Azul, I walk around with a 0.5msec stick...

OS related stuff
(once GC and TTSP are taken care of)
OS related hiccups tend to dominate once GC and TTSP
are removed as issues.

Take scheduling pressure seriously (Duh?)

Hyper-threading (good? bad? yes!)

Swapping (Duh!)

Power management

Transparent Huge Pages (THP).

...

Shameless bragging


Zing
A JVM for Linux/x86 servers

ELIMINATES Garbage Collection as a concern for
enterprise applications

Very wide operating range: Used in both low latency and
large scale enterprise application spaces

Decouples scale metrics from response time concerns

Transaction rate, data set size, concurrent users,
heap size, allocation rate, mutation rate, etc.

Leverages elastic memory for resilient operation

What is Zing good for?
If you have a server-based Java application

And you are running on Linux

And you use using more than ~300MB of memory

Then Zing will likely deliver superior behavior
metrics


Where Zing shines
Low latency

Eliminate behavior blips down to the sub-millisecond-units level

Machine-to-machine “stuff”

Support higher *sustainable* throughput (the one that meets SLAs)

Human response times

Eliminate user-annoying response time blips. Multi-second and even
fraction-of-a-second blips will be completely gone.

Support larger memory JVMs *if needed* (e.g. larger virtual user
counts, or larger cache, in-memory state, or consolidating multiple
instances)

“Large” data and in-memory analytics

Make batch stuff “business real time”. Gain super-efﬁciencies.

One-liner Takeaway:

Zing: A cure for the Java hiccups


Q&A
!

http:/
/www.azulsystems.com
!

http:/
/www.jhiccup.com
http:/
/giltene.github.com/HdrHistogram
http:/
/latencyutils.github.com/LatencyUtils


Watch the video with slide synchronization on
InfoQ.com!
http://www.infoq.com/presentations/javatuning-latency

Enabling Java in Latency Sensitive Environments

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (11)

En vedette

En vedette (9)

Similaire à Enabling Java in Latency Sensitive Environments

Similaire à Enabling Java in Latency Sensitive Environments (20)

Plus de C4Media

Plus de C4Media (20)

Dernier

Dernier (20)

Enabling Java in Latency Sensitive Environments