<s>
Eclipse	B-Language
OpenJ9	I-Language
(	O
previously	O
known	O
as	O
IBM	B-Language
J9	I-Language
)	O
is	O
a	O
high	O
performance	O
,	O
scalable	O
,	O
Java	B-Language
virtual	I-Language
machine	I-Language
(	O
JVM	B-Language
)	O
implementation	O
that	O
is	O
fully	O
compliant	O
with	O
the	O
Java	B-Language
Virtual	I-Language
Machine	I-Language
Specification	I-Language
.	O
</s>
<s>
OpenJ9	B-Language
can	O
be	O
built	O
from	O
source	O
,	O
or	O
can	O
be	O
used	O
with	O
prebuilt	O
binaries	O
available	O
at	O
the	O
AdoptOpenJDK	B-Language
project	O
for	O
a	O
number	O
of	O
platforms	O
including	O
Linux	B-Application
and	O
Windows	B-Application
.	O
</s>
<s>
OpenJ9	B-Language
is	O
also	O
a	O
core	O
component	O
of	O
the	O
IBM	O
developer	O
kit	O
,	O
which	O
is	O
embedded	O
in	O
many	O
IBM	O
middleware	O
products	O
,	O
including	O
WebSphere	B-Language
Application	I-Language
Server	I-Language
and	O
Websphere	O
Liberty	O
.	O
</s>
<s>
OpenJ9	B-Language
is	O
also	O
a	O
component	O
of	O
Open	O
Liberty	O
.	O
</s>
<s>
Extensive	O
configuration	O
options	O
ensure	O
that	O
the	O
JVM	B-Language
can	O
be	O
tuned	O
to	O
satisfy	O
the	O
requirements	O
of	O
a	O
wide	O
range	O
of	O
Java	B-Language
applications	O
,	O
from	O
complex	O
enterprise	O
applications	O
that	O
run	O
on	O
mainframe	O
hardware	O
to	O
short-lived	O
applications	O
that	O
run	O
on	O
container-based	O
cloud	O
services	O
.	O
</s>
<s>
OpenJ9	B-Language
can	O
trace	O
its	O
roots	O
back	O
to	O
the	O
ENVY/Smalltalk	O
product	O
developed	O
by	O
Object	O
Technology	O
International	O
(	O
OTI	O
)	O
.	O
</s>
<s>
IBM	O
purchased	O
OTI	O
in	O
1996	O
for	O
their	O
Smalltalk	B-Application
expertise	O
and	O
products	O
.	O
</s>
<s>
However	O
,	O
when	O
the	O
Java	B-Language
language	I-Language
emerged	O
as	O
a	O
leading	O
language	O
for	O
the	O
enterprise	O
market	O
,	O
the	O
existing	O
Smalltalk	B-Application
VM	O
was	O
adapted	O
to	O
process	O
Java	B-Language
bytecodes	O
instead	O
.	O
</s>
<s>
The	O
name	O
J9	O
evolved	O
from	O
the	O
naming	O
convention	O
for	O
the	O
Smalltalk	B-Application
source	O
code	O
,	O
K8	O
.	O
</s>
<s>
K	O
→	O
J	O
(	O
a	O
backward	O
step	O
)	O
because	O
the	O
developers	O
believed	O
that	O
Smalltalk	B-Application
was	O
better	O
than	O
Java	B-Language
,	O
but	O
8	O
→	O
9	O
(	O
a	O
forward	O
step	O
)	O
because	O
the	O
new	O
VM	O
would	O
be	O
better	O
than	O
before	O
.	O
</s>
<s>
The	O
J9	O
JVM	B-Language
became	O
the	O
runtime	O
engine	O
for	O
many	O
of	O
IBM	O
's	O
enterprise	O
middleware	O
products	O
,	O
where	O
it	O
has	O
built	O
its	O
reputation	O
for	O
high	O
performance	O
,	O
scalability	O
,	O
and	O
reliability	O
.	O
</s>
<s>
In	O
2017	O
,	O
J9	O
became	O
an	O
Eclipse	B-Application
Foundation	I-Application
project	O
under	O
the	O
name	O
Eclipse	B-Language
OpenJ9	I-Language
.	O
</s>
<s>
IBM	O
continue	O
to	O
be	O
actively	O
involved	O
in	O
the	O
project	O
and	O
continue	O
to	O
put	O
this	O
Java	B-Language
VM	I-Language
at	O
the	O
core	O
of	O
many	O
software	O
offerings	O
.	O
</s>
<s>
At	O
the	B-Application
Eclipse	I-Application
Foundation	I-Application
,	O
OpenJ9	B-Language
is	O
classified	O
as	O
an	O
incubator	O
project	O
,	O
with	O
the	O
first	O
release	O
,	O
v0.8.0	O
,	O
delivered	O
in	O
2018	O
.	O
</s>
<s>
The	O
Eclipse	B-Language
OpenJ9	I-Language
JVM	B-Language
is	O
fully	O
compliant	O
with	O
the	O
Java	B-Language
JVM	B-Language
specification	O
.	O
</s>
<s>
The	O
same	O
version	O
of	O
the	O
JVM	B-Language
can	O
be	O
used	O
in	O
OpenJDK	O
8	O
and	O
later	O
releases	O
,	O
which	O
means	O
that	O
many	O
features	O
and	O
improvements	O
can	O
be	O
exploited	O
by	O
applications	O
that	O
run	O
on	O
different	O
versions	O
of	O
Java	B-Language
.	O
</s>
<s>
Compared	O
to	O
Oracle	B-Application
's	O
HotSpot	B-Language
VM	O
,	O
OpenJ9	B-Language
touts	O
higher	O
start-up	O
performance	O
and	O
lower	O
memory	O
consumption	O
at	O
a	O
similar	O
overall	O
throughput	O
.	O
</s>
<s>
Eclipse	B-Language
OpenJ9	I-Language
embeds	O
Eclipse	B-Application
OMR	O
,	O
which	O
provides	O
core	O
runtime	O
components	O
that	O
can	O
be	O
used	O
to	O
build	O
runtime	O
environments	O
for	O
different	O
programming	O
languages	O
.	O
</s>
<s>
At	O
the	O
OpenJ9	B-Language
project	O
,	O
an	O
extra	O
layer	O
of	O
code	O
adds	O
the	O
language	O
semantics	O
to	O
provide	O
a	O
runtime	O
environment	O
for	O
Java	B-Language
applications	O
.	O
</s>
<s>
The	O
components	O
that	O
make	O
up	O
Eclipse	B-Language
OpenJ9	I-Language
are	O
described	O
in	O
the	O
following	O
sections	O
:	O
</s>
<s>
The	O
Just-In-Time	O
(	O
JIT	O
)	O
improves	O
the	O
performance	O
of	O
Java	B-Language
applications	O
by	O
compiling	O
platform-neutral	O
Java	B-Language
bytecode	O
into	O
native	O
machine	O
code	O
at	O
run	O
time	O
.	O
</s>
<s>
Instead	O
,	O
OpenJ9	B-Language
records	O
the	O
number	O
of	O
times	O
a	O
method	O
is	O
called	O
and	O
triggers	O
JIT	O
compilation	O
at	O
a	O
predefined	O
threshold	O
.	O
</s>
<s>
Ahead	B-Application
of	I-Application
Time	I-Application
(	O
AOT	B-Application
)	O
compilation	O
is	O
a	O
mechanism	O
for	O
improving	O
start	O
up	O
performance	O
.	O
</s>
<s>
Methods	O
are	O
dynamically	O
compiled	O
into	O
AOT	B-Application
code	O
at	O
runtime	O
,	O
which	O
enables	O
the	O
JVM	B-Language
to	O
start	O
an	O
application	O
faster	O
.	O
</s>
<s>
AOT	B-Application
is	O
enabled	O
automatically	O
when	O
class	O
data	O
sharing	O
is	O
used	O
(	O
-Xshareclasses	O
)	O
and	O
does	O
n't	O
require	O
any	O
special	O
tuning	O
.	O
</s>
<s>
OpenJ9	B-Language
automatically	O
chooses	O
which	O
methods	O
to	O
compile	O
based	O
on	O
heuristics	O
that	O
identify	O
the	O
start-up	O
phase	O
of	O
large	O
applications	O
.	O
</s>
<s>
For	O
small	O
or	O
short	O
running	O
applications	O
,	O
the	O
-Xtune:virtualized	O
option	O
should	O
be	O
added	O
to	O
get	O
the	O
most	O
out	O
of	O
AOT-compiled	O
code	O
.	O
</s>
<s>
Sharing	O
class	O
data	O
between	O
JVMs	B-Language
has	O
two	O
main	O
benefits	O
:	O
</s>
<s>
Memory	O
footprint	O
is	O
reduced	O
by	O
sharing	O
common	O
classes	O
between	O
applications	O
that	O
run	O
in	O
separate	O
Java	B-Language
VMs	I-Language
.	O
</s>
<s>
Unlike	O
other	O
class	O
data	O
sharing	O
(	O
CDS	O
)	O
implementations	O
,	O
enabling	O
the	O
feature	O
in	O
OpenJ9	B-Language
requires	O
only	O
one	O
step	O
:	O
setting	O
-Xshareclasses	O
on	O
the	O
command	O
line	O
when	O
you	O
start	O
your	O
application	O
.	O
</s>
<s>
When	O
specified	O
,	O
OpenJ9	B-Language
creates	O
a	O
memory	O
mapped	O
file	O
to	O
store	O
and	O
share	O
the	O
classes	O
in	O
memory	O
.	O
</s>
<s>
By	O
default	O
,	O
OpenJ9	B-Language
always	O
shares	O
both	O
the	O
bootstrap	O
and	O
application	O
classes	O
that	O
are	O
loaded	O
by	O
the	O
default	O
system	O
class	O
loader	O
.	O
</s>
<s>
Another	O
benefit	O
of	O
the	O
OpenJ9	B-Language
CDS	O
implementation	O
is	O
that	O
the	O
cache	O
is	O
updated	O
dynamically	O
.	O
</s>
<s>
So	O
when	O
an	O
application	O
loads	O
new	O
classes	O
,	O
the	O
JVM	B-Language
automatically	O
stores	O
them	O
in	O
the	O
cache	O
without	O
any	O
user	O
intervention	O
.	O
</s>
<s>
OpenJ9	B-Language
also	O
provides	O
a	O
public	O
Helper	O
API	O
for	O
integrating	O
class	O
sharing	O
support	O
into	O
custom	O
class	O
loaders	O
,	O
plus	O
several	O
utilities	O
for	O
managing	O
active	O
caches	O
.	O
</s>
<s>
To	O
prevent	O
applications	O
running	O
out	O
of	O
memory	O
,	O
objects	O
in	O
the	O
Java	B-Language
heap	O
that	O
are	O
no	O
longer	O
required	O
must	O
be	O
reclaimed	O
.	O
</s>
<s>
This	O
process	O
is	O
known	O
as	O
garbage	B-General_Concept
collection	I-General_Concept
(	O
GC	O
)	O
.	O
</s>
<s>
OpenJ9	B-Language
provides	O
a	O
number	O
of	O
garbage	B-General_Concept
collection	I-General_Concept
policies	O
that	O
are	O
designed	O
around	O
different	O
types	O
of	O
applications	O
and	O
workloads	O
.	O
</s>
<s>
By	O
default	O
,	O
OpenJ9	B-Language
uses	O
the	O
Generational	O
Concurrent	O
(	O
-Xgcpolicy:gencon	O
)	O
policy	O
,	O
which	O
is	O
best	O
suited	O
to	O
transactional	O
applications	O
that	O
have	O
many	O
short	O
lived	O
objects	O
.	O
</s>
<s>
Alternative	O
policies	O
are	O
available	O
,	O
including	O
those	O
that	O
cater	O
for	O
applications	O
with	O
large	O
Java	B-Language
heaps	O
(	O
-Xgcpolicy:balanced	O
)	O
,	O
applications	O
that	O
are	O
sensitive	O
to	O
response-time	O
(	O
-Xgcpolicy:metronome	O
)	O
,	O
or	O
applications	O
that	O
require	O
high	O
application	O
throughput	O
(	O
-Xgcpolicy:optthruput	O
)	O
.	O
</s>
<s>
An	O
"	O
idle	O
tuning	O
"	O
option	O
(	O
)	O
triggers	O
garbage	B-General_Concept
collection	I-General_Concept
in	O
OpenJ9	B-Language
when	O
the	O
application	O
is	O
idle	O
.	O
</s>
<s>
Doing	O
this	O
reduces	O
memory	O
footprint	O
,	O
meaningful	O
for	O
some	O
virtual	B-Architecture
hosting	I-Architecture
billing	O
plans	O
.	O
</s>
<s>
In	O
January	O
2020	O
,	O
OpenJ9	B-Language
delivered	O
an	O
experimental	O
feature	O
to	O
JIT	O
compile	O
code	O
outside	O
JVM	B-Language
and	O
remotely	O
on	O
a	O
server	O
.	O
</s>
<s>
OpenJ9	B-Language
contains	O
extensive	O
trace	O
and	O
debugging	O
utilities	O
to	O
help	O
identify	O
,	O
isolate	O
and	O
solve	O
runtime	O
problems	O
.	O
</s>
<s>
These	O
are	O
produced	O
when	O
the	O
JVM	B-Language
ends	O
unexpectedly	O
because	O
of	O
an	O
operating	O
system	O
signal	O
,	O
OutOfMemoryError	O
exception	O
,	O
or	O
a	O
user	O
initiated	O
keystroke	O
combination	O
.	O
</s>
<s>
Java	B-Language
dumps	O
summarize	O
the	O
state	O
of	O
the	O
JVM	B-Language
when	O
the	O
event	O
occurs	O
,	O
with	O
most	O
of	O
the	O
information	O
relating	O
to	O
components	O
of	O
the	O
JVM	B-Language
.	O
</s>
<s>
Heap	O
dumps	O
show	O
all	O
the	O
live	O
objects	O
on	O
the	O
Java	B-Language
heap	O
when	O
the	O
JVM	B-Language
ends	O
because	O
of	O
an	O
OutOfMemoryError	O
exception	O
or	O
when	O
requested	O
by	O
a	O
user	O
.	O
</s>
<s>
Analyzing	O
heap	O
dumps	O
might	O
tell	O
you	O
which	O
objects	O
are	O
using	O
large	O
amounts	O
of	O
memory	O
on	O
the	O
Java	B-Language
heap	O
and	O
why	O
these	O
are	O
not	O
being	O
garbage	B-General_Concept
collected	I-General_Concept
.	O
</s>
<s>
Often	O
known	O
as	O
core	B-Error_Name
dumps	I-Error_Name
,	O
these	O
are	O
platform-specific	O
and	O
contain	O
a	O
raw	O
binary	O
dump	O
of	O
the	O
process	O
memory	O
.	O
</s>
<s>
This	O
dump	O
has	O
a	O
complete	O
copy	O
of	O
the	O
Java	B-Language
heap	O
,	O
including	O
the	O
contents	O
of	O
all	O
Java	B-Language
objects	O
in	O
the	O
application	O
.	O
</s>
<s>
OpenJ9	B-Language
tools	O
are	O
available	O
to	O
process	O
the	O
system	O
dump	O
into	O
a	O
readable	O
format	O
for	O
analysis	O
.	O
</s>
<s>
To	O
analyze	O
garbage	B-General_Concept
collection	I-General_Concept
problems	O
you	O
can	O
enable	O
verbose	O
logging	O
,	O
which	O
provides	O
data	O
on	O
all	O
garbage	B-General_Concept
collection	I-General_Concept
operations	O
including	O
initialization	O
,	O
stop-the-world	O
processing	O
,	O
finalization	O
,	O
reference	O
processing	O
,	O
and	O
allocation	O
failures	O
.	O
</s>
<s>
For	O
even	O
more	O
detailed	O
analysis	O
,	O
you	O
can	O
turn	O
on	O
garbage	B-General_Concept
collection	I-General_Concept
tracing	O
.	O
</s>
<s>
The	O
OpenJ9	B-Language
trace	O
facility	O
can	O
be	O
used	O
to	O
trace	O
applications	O
,	O
Java	B-Language
methods	O
,	O
or	O
internal	O
JVM	B-Language
operations	O
with	O
minimal	O
impact	O
on	O
performance	O
.	O
</s>
<s>
If	O
a	O
general	O
protection	O
fault	O
or	O
abort	O
event	O
takes	O
place	O
,	O
the	O
JIT	O
produces	O
a	O
small	O
binary	O
dump	O
that	O
can	O
be	O
analyzed	O
by	O
OpenJ9	B-Language
developers	O
to	O
help	O
determine	O
the	O
root	O
cause	O
.	O
</s>
<s>
DTFJ	O
works	O
with	O
data	O
from	O
a	O
system	O
dump	O
or	O
a	O
Java	B-Language
dump	O
.	O
</s>
<s>
AdoptOpenJDK	B-Language
:	O
Community	O
builds	O
of	O
OpenJDK	O
with	O
OpenJ9	B-Language
are	O
built	O
and	O
tested	O
at	O
the	O
AdoptOpenJDK	B-Language
project	O
(	O
DEPRECATED	O
:	O
Transferred	O
to	O
IBM	O
as	O
Semeru	O
)	O
.	O
</s>
<s>
OpenJ9	B-Language
is	O
a	O
component	O
of	O
the	O
.	O
</s>
<s>
AdoptOpenJDK	B-Language
OpenJDK	O
with	O
OpenJ9	B-Language
community	O
builds	O
are	O
now	O
built	O
,	O
tested	O
and	O
distributed	O
as	O
.	O
</s>
<s>
Apache	B-General_Concept
OpenWhisk	I-General_Concept
:	O
OpenWhisk	B-General_Concept
is	O
using	O
OpenJ9	B-Language
as	O
the	O
JVM	B-Language
for	O
the	O
.	O
</s>
<s>
Eclipse	B-Application
IDE	I-Application
:	O
The	B-Application
Eclipse	I-Application
Foundation	I-Application
have	O
approved	O
the	O
inclusion	O
of	O
OpenJDK	O
8	O
with	O
OpenJ9	B-Language
in	O
the	O
Eclipse	B-Application
Integrated	B-Application
Development	I-Application
Environment	I-Application
(	O
IDE	O
)	O
.	O
</s>
