The document discusses Coordinated Restore at Checkpoint (CRaC), a feature of the Java Virtual Machine (JVM) that allows saving the state of a running application and restoring it later to avoid JVM startup overhead. CRaC uses the CRIU userspace checkpoint/restore mechanism and provides a simple API for applications to register resources that need to be notified during checkpoint and restore. This allows restoring application state like open files and sockets. An example demonstrates how CRaC can speed up subsequent runs of an application by restoring a pre-filled cache from a previous checkpoint.

1. What the CRaC...
Coordinated Restore at Checkpoint
on the Java Virtual Machine

2. Gerrit Grunwald | Developer Advocate | Azul
ABOUTME.

3. JAVA IS
GREAT...

4. VIBRANT
COMMUNITY...

5. HUNDREDS OF
JUGs...

6. THOUSANDS OF
FOSS PROJECTS...

7. JAVA VIRTUAL
MACHINE
JAVA VIRTUAL
MACHINE

8. HOW DOES
IT WORK...

9. MyClass.java MyClass.class
SOURCE CODE COMPILER BYTE CODE

10. MyClass.class
BYTE CODE CLASS LOADER JVM MEMORY

11. JVM MEMORY
􀊫􀈒
EXECUTION ENGINE

12. EXECUTION ENGINE
Interpreter C1 JIT
Compiler
(client)
C2 JIT
Compiler
(server)
􀊫
Pro
fi
ler
􀈒
Garbage
Collector

13. EXECUTION ENGINE
Interpreter C1 JIT
Compiler
(client)
C2 JIT
Compiler
(server)

14. instruction set of CPU
Detects hot spots by
counting method calls
JVM
THRESHOLD
REACHED

15. Pass the hot spot methods
to C1 JIT Compiler
JVM C1 JIT
COMPILER
Compiles code as quickly
as possible with low optimisation

16. C1 JIT
COMPILER
Compiles code as quickly
as possible with low optimisation
Pro
fi
les the running code
(detecting hot code)
JVM
THRESHOLD
REACHED

17. Pass the "hot" code
to C2 JIT Compiler
JVM C2 JIT
COMPILER
Compiles code with best
optimisation possible (slower)

18. TIERED
COMPILATION

19. Level 0 - Interpreted code
Level 1 - C1 compiled code (no pro
fi
ling)
Level 2 - C1 compiled code (basic pro
fi
ling)
Level 3 - C1 compiled code (full pro
fi
ling, ~35% overhead)
Level 4 - C2 compiled code (uses pro
fi
le data from previous steps)
LEVELS OF EXECUTION

20. Level 0 - Interpreted code
Level 1 - C1 compiled code (no pro
fi
ling)
Level 2 - C1 compiled code (basic pro
fi
ling)
Level 3 - C1 compiled code (full pro
fi
ling, ~35% overhead)
Level 4 - C2 compiled code (uses pro
fi
le data from previous steps)
LEVELS OF EXECUTION
PREFERRED

21. EXECUTION
CYCLE

22. EXECUTION CYCLE
Slow
(Execution Level 0)

23. EXECUTION CYCLE
Finding
"hotspots"
Slow
(Execution Level 0)

24. EXECUTION CYCLE
Fast compile,
low optimisation
(Execution Level 3)
Finding
"hotspots"
Slow
(Execution Level 0)

25. EXECUTION CYCLE
Finding
"hot code"
Fast compile,
low optimisation
(Execution Level 3)
Finding
"hotspots"
Slow
(Execution Level 0)

26. EXECUTION CYCLE
Slower compile,
high optimisation
(Execution Level 4)
Finding
"hot code"
Fast compile,
low optimisation
(Execution Level 3)
Finding
"hotspots"
Slow
(Execution Level 0)

27. EXECUTION CYCLE
Can happen
(performance hit)
Slower compile,
high optimisation
(Execution Level 4)
Finding
"hot code"
Fast compile,
low optimisation
(Execution Level 3)
Finding
"hotspots"
Slow
(Execution Level 0)

28. DEOPTIMISATION

29. DEOPTIMISATION
if (value > 0)
result = 3; result = 0;
print(result);
TRUE FALSE
CODE

30. DEOPTIMISATION
if (value > 0)
result = 3; result = 0;
print(result);
TRUE FALSE
CODE
Hot Path (pro
fi
led)

31. DEOPTIMISATION
if (value > 0)
result = 3; result = 0;
print(result);
TRUE FALSE
CODE
guard (value > 0)
result = 3;
print(result);
DEOPTIMISE
TRUE FALSE
OPTIMIZED CODE

32. DEOPTIMISATION
if (value > 0)
result = 3; result = 0;
print(result);
TRUE FALSE
CODE
guard (value > 0)
result = 3;
print(result);
DEOPTIMISE
TRUE FALSE
OPTIMIZED CODE
value = 3

33. DEOPTIMISATION
if (value > 0)
result = 3; result = 0;
print(result);
TRUE FALSE
CODE
guard (value > 0)
result = 3;
print(result);
DEOPTIMISE
TRUE FALSE
OPTIMIZED CODE
value = 0

34. THAT'S
GREAT...

35. ...BUT...

36. ...IT TAKES
TIME !

37. JVM PERFORMANCE GRAPH
JVM STARTUP
GarbageCollector pauses
Deoptimisations

38. MICROSERVICE
ENVIRONMENT

39. MICROSERVICE ENVIRONMENT
FIRST RUN
JVM STARTUP
SECOND RUN
JVM STARTUP
THIRD RUN
JVM STARTUP

41. WOULDN'T IT BE GREAT...?
FIRST RUN
JVM STARTUP
SECOND RUN
NO STARTUP OVERHEAD
THIRD RUN
NO STARTUP OVERHEAD

42. SOLUTIONS...?

43. CLASS DATA
SHARING

44. WHAT ABOUT CDS?
Class Data Sharing (App/Dynamic)
Dump internal class representation into
fi
le
Shared on each JVM start (CDS)
No optimization or hotspot detection
Only reduces loading time of classes
Start up could be up to 1-2 seconds faster

45. MyClass.class
BYTE CODE CLASS LOADER JVM MEMORY
CDS

46. AHEAD OF TIME
COMPILATION

47. WHY NOT USE AOT?
No interpreting bytecodes
No analysis of hotspots
No runtime compilation of code
Start at full speed, straight away
GraalVM native image does that
PROBLEM SOLVED...?

48. NOT SO FAST...
AOT is, by de
fi
nition, static
Code is compiled before it is run
Compiler has no knowledge of how the
code will actually run
Pro
fi
le Guided Optimisation (PGO)
can partially help

49. JVM PERFORMANCE GRAPH
AOT Compiled Code
AOT Compiled Code with Profile Guided Optimisation
Needs to run once for pro
fi
ling

50. AOT VS JIT
Limited use of method inlining
No runtime bytecode generation
Re
fl
ection is possible but complicated
Unable to use speculative optimisations
Overall performance will typically be lower
Deployed env != Development env.
Full speed from the start
No overhead to compile code at runtime
Small memory footprint
Can use aggressive method inlining at runtime
Can use runtime bytecode generation
Re
fl
ection is simple
Can use speculative optimisations
Overall performance will typically be higher
Deployed env. == Development env.
Requires more time to start up
Overhead to compile code at runtime
Larger memory footprint
AOT JIT

51. JIT DISADVANTAGES
Requires more time to start up
CPU overhead to compile code at runtime
Larger memory footprint

52. AOT JIT
Reduced
Max Latency
Peak Throughput
Small Packaging
Startup Speed
Low Memory
Footprint
(Chart by Thomas Wuerthinger)

53. A DIFFERENT
APPROACH

54. CRIU
CHECKPOINT RESTORE IN USERSPACE

55. Linux project
Part of kernel >= 3.11 (2013)
Freeze a running container/application
Checkpoint its state to disk
Restore the container/application from the saved data.
Used by/integrated in OpenVZ, LXC/LXD, Docker,
Podman and others
CHECKPOINT RESTORE IN UUSERSPACE

56. Mainly implemented in userspace (not kernel)
Main goal is migration of containers for microservices
Heavily relies on /proc
fi
le system
It can checkpoint:
Processes and threads
Application memory, memory mapped
fi
les and shared memory
Open
fi
les, pipes and FIFOs
Sockets
Interprocess communication channels
Timers and signals
Can rebuild TCP connection from one side without need to exchange packets
CHECKPOINT RESTORE IN UUSERSPACE

57. Restart from saved state on another machine
(open
fi
les, shared memory etc.)
Start multiple instances of same state on same machine
(PID will be restored which will lead to problems)
A Java Virtual Machine would assume it was continuing its tasks
(very dif
fi
cult to use effectively)
CRIU CHALLENGES

58. CRaC
Coordinated Restore at Checkpoint

59. CRaC
CRIU comes bundled with the JDK
Heap is cleaned, compacted (JVM is in a safe state)
Throws CheckpointException (in case of open
fi
les/sockets)
Comes with a simple API
Creates checkpoints using code or jcmd
Uses JVM safepoint mechanism (to stop threads etc.)

60. openjdk.org/projects/crac
Lead by Anton Kozlov (Azul)

61. RUNNING APPLICATION
Aware of checkpoint
being created
RUNNING APPLICATION
Aware of restore
happening
CRaC has more restrictions (e.g. no open
fi
les, sockets etc.)
CRaC

62. CRaC
START
>java -XX:CRaCCheckpointTo=PATH -jar app.jar
RESTORE
>java -XX:CRaCRestoreFrom=PATH

63. CRaC API

64. <<interface>>
Resource
beforeCheckpoint()
afterRestore()
CRaC uses Resources that can be
noti
fi
ed about a Checkpoint and
Restore
Classes in application code
implement the Resource interface
The application receives callbacks
during checkpointing and
restoring
Makes it possible to close/restore
resources (e.g. open
fi
les, sockets)
CRaC API

65. Resource objects need to be registered with a Context so that they
can receive noti
fi
cations
There is a global Context accessible via the static
getGlobalContext() method of the Core class
CRaC API

66. <<interface>>
Resource
beforeCheckpoint()
afterRestore()
Core
getGlobalContext()
CRaC API
<<abstract>>
Context
register(Resource)

67. CRaC API
The global Context maintains a list of Resource objects
The beforeCheckpoint() methods are called in the reverse order the
Resource objects were added
The afterRestore() methods are called in the order the Resource
objects were added
Checkpoint and restore can be done programmatically by using
Core.checkpointRestore()
Checkpoint can also be created by jcmd

68. SIMPLE
EXAMPLE

69. SIMPLE EXAMPLE
Loop 100000x
Random number
1 - 100000
isPrime(number)
Cache
Scheduled Thread
Executed every
5 seconds

70. SIMPLE EXAMPLE
Loop 100000x
Random number
1 - 100000
isPrime(number)
Cache
Scheduled Thread
Executed every
5 seconds

71. SIMPLE EXAMPLE
Loop 100000x
Random number
1 - 100000
isPrime(number)
Is result for number
in cache?
Cache
Scheduled Thread
Executed every
5 seconds

72. SIMPLE EXAMPLE
Loop 100000x
Random number
1 - 100000
isPrime(number)
Is result for number
in cache?
Cache
Scheduled Thread
Executed every
5 seconds

73. SIMPLE EXAMPLE
Loop 100000x
Random number
1 - 100000
isPrime(number)
Is result for number
in cache?
yes
Cache
FAST
Scheduled Thread
Executed every
5 seconds

74. SIMPLE EXAMPLE
Loop 100000x
Random number
1 - 100000
isPrime(number)
Is result for number
in cache?
Calculate if prime
no
Cache
Scheduled Thread
Executed every
5 seconds

75. SIMPLE EXAMPLE
Loop 100000x
Random number
1 - 100000
isPrime(number)
Is result for number
in cache?
Calculate if prime
Result
no
Cache
Scheduled Thread
Executed every
5 seconds

76. SIMPLE EXAMPLE
Loop 100000x
Random number
1 - 100000
isPrime(number)
Is result for number
in cache?
Calculate if prime
Result
no
Cache
Scheduled Thread
Executed every
5 seconds

77. SIMPLE EXAMPLE
Loop 100000x
Random number
1 - 100000
isPrime(number)
Is result for number
in cache?
Calculate if prime
Result
no
Cache
SLOW
Scheduled Thread
Executed every
5 seconds

78. SIMPLE EXAMPLE
Loop 100000x
Random number
1 - 100000
isPrime(number)
Is result for number
in cache?
Calculate if prime
Result
no
Cache
Scheduled Thread
Executed every
5 seconds
timeout 50 sec

79. SIMPLE EXAMPLE
First run is slow because the cache is empty
Time to check 100 000 random numbers for
prime should decrease with every run

80. Application Performance
0
0.2
0.4
0.6
0.8
1
Iterations
1 2 3 4 5 6 7 8 9 10 11 12
SIMPLE EXAMPLE

81. DEMO...

82. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

83. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
>
De
fi
nes where to store
fi
les
for the checkpoint
SIMPLE EXAMPLE
SHELL 1 SHELL 2

84. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

85. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

86. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

87. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
>
SIMPLE EXAMPLE
Slow because cache is not
fi
lled yet
SHELL 1 SHELL 2

88. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

89. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

90. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

91. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

92. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

93. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

94. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

95. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

96. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
10. Run: 20 ms (99992 elements cached, 100.0%)
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

97. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
10. Run: 20 ms (99992 elements cached, 100.0%)
11. Run: 17 ms (99999 elements cached, 100.0%)
>
SIMPLE EXAMPLE
SHELL 1 SHELL 2

98. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
10. Run: 20 ms (99992 elements cached, 100.0%)
11. Run: 17 ms (99999 elements cached, 100.0%)
>
SIMPLE EXAMPLE
Fast because cache is
fi
lled
SHELL 1 SHELL 2

99. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
10. Run: 20 ms (99992 elements cached, 100.0%)
11. Run: 17 ms (99999 elements cached, 100.0%)
SIMPLE EXAMPLE
>jcmd crac4.jar JDK.checkpoint
SHELL 1 SHELL 2

100. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
10. Run: 20 ms (99992 elements cached, 100.0%)
11. Run: 17 ms (99999 elements cached, 100.0%)
SIMPLE EXAMPLE
>jcmd crac4.jar JDK.checkpoint CREATE CHECKPOINT
SHELL 1 SHELL 2

101. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
10. Run: 20 ms (99992 elements cached, 100.0%)
11. Run: 17 ms (99999 elements cached, 100.0%)
beforeCheckpoint() called in Main
beforeCheckpoint() called in GenericCache
CR: Checkpoint ...
Killed
>
SIMPLE EXAMPLE
>jcmd crac4.jar JDK.checkpoint
4240:
Command executed successfully
>
SHELL 1 SHELL 2

102. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
10. Run: 20 ms (99992 elements cached, 100.0%)
11. Run: 17 ms (99999 elements cached, 100.0%)
beforeCheckpoint() called in Main
beforeCheckpoint() called in GenericCache
CR: Checkpoint ...
Killed
>
SIMPLE EXAMPLE
>jcmd crac4.jar JDK.checkpoint
4240:
Command executed successfully
>
SHELL 1 SHELL 2

103. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
10. Run: 20 ms (99992 elements cached, 100.0%)
11. Run: 17 ms (99999 elements cached, 100.0%)
beforeCheckpoint() called in Main
beforeCheckpoint() called in GenericCache
CR: Checkpoint ...
Killed
>java -XX:CRaCRestoreFrom=/crac-files
SIMPLE EXAMPLE
>jcmd crac4.jar JDK.checkpoint
4240:
Command executed successfully
>
SHELL 1 SHELL 2

104. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
10. Run: 20 ms (99992 elements cached, 100.0%)
11. Run: 17 ms (99999 elements cached, 100.0%)
beforeCheckpoint() called in Main
beforeCheckpoint() called in GenericCache
CR: Checkpoint ...
Killed
>java -XX:CRaCRestoreFrom=/crac-files
SIMPLE EXAMPLE
>jcmd crac4.jar JDK.checkpoint
4240:
Command executed successfully
>
RESTORE
SHELL 1 SHELL 2

105. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
10. Run: 20 ms (99992 elements cached, 100.0%)
11. Run: 17 ms (99999 elements cached, 100.0%)
beforeCheckpoint() called in Main
beforeCheckpoint() called in GenericCache
CR: Checkpoint ...
Killed
>java -XX:CRaCRestoreFrom=/crac-files
afterRestore() called in GenericCache
afterRestore() called in Main
12. Run: 23 ms (99999 elements cached, 100.0%)
SIMPLE EXAMPLE
>jcmd crac4.jar JDK.checkpoint
4240:
Command executed successfully
>
SHELL 1 SHELL 2

106. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
10. Run: 20 ms (99992 elements cached, 100.0%)
11. Run: 17 ms (99999 elements cached, 100.0%)
beforeCheckpoint() called in Main
beforeCheckpoint() called in GenericCache
CR: Checkpoint ...
Killed
>java -XX:CRaCRestoreFrom=/crac-files
afterRestore() called in GenericCache
afterRestore() called in Main
12. Run: 23 ms (99999 elements cached, 100.0%)
SIMPLE EXAMPLE
>jcmd crac4.jar JDK.checkpoint
4240:
Command executed successfully
>
Continues to run...fast
SHELL 1 SHELL 2

107. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
10. Run: 20 ms (99992 elements cached, 100.0%)
11. Run: 17 ms (99999 elements cached, 100.0%)
beforeCheckpoint() called in Main
beforeCheckpoint() called in GenericCache
CR: Checkpoint ...
Killed
>java -XX:CRaCRestoreFrom=/crac-files
afterRestore() called in GenericCache
afterRestore() called in Main
12. Run: 23 ms (99999 elements cached, 100.0%)
13. Run: 21 ms (99995 elements cached, 100.0%)
SIMPLE EXAMPLE
>jcmd crac4.jar JDK.checkpoint
4240:
Command executed successfully
>
SHELL 1 SHELL 2

108. >java -XX:CRaCCheckpointTo=/crac-files -jar crac4.jar
Running on CRaC (PID 4240)
First run will take up to 30 seconds...
Register Resource: GenericCache
Register Resource: Main
1. Run: 27863 ms (63303 elements cached, 63.3%)
2. Run: 10611 ms (86580 elements cached, 86.6%)
3. Run: 3965 ms (95161 elements cached, 95.2%)
4. Run: 1428 ms (98245 elements cached, 98.2%)
5. Run: 533 ms (99340 elements cached, 99.3%)
6. Run: 207 ms (99750 elements cached, 99.8%)
7. Run: 87 ms (99898 elements cached, 99.9%)
8. Run: 42 ms (99960 elements cached, 100.0%)
9. Run: 25 ms (99986 elements cached, 100.0%)
10. Run: 20 ms (99992 elements cached, 100.0%)
11. Run: 17 ms (99999 elements cached, 100.0%)
beforeCheckpoint() called in Main
beforeCheckpoint() called in GenericCache
CR: Checkpoint ...
Killed
>java -XX:CRaCRestoreFrom=/crac-files
afterRestore() called in GenericCache
afterRestore() called in Main
12. Run: 23 ms (99999 elements cached, 100.0%)
13. Run: 21 ms (99995 elements cached, 100.0%)
14. Run: 24 ms (99997 elements cached, 100.0%)
SIMPLE EXAMPLE
>jcmd crac4.jar JDK.checkpoint
4240:
Command executed successfully
>
SHELL 1 SHELL 2

109. FROM THE COMMAND LINE:
>jcmd YOUR_AWESOME.jar JDK.checkpoint
CREATING A CHECKPOINT

110. CREATING A CHECKPOINT
FROM CODE:
Core.checkpointRestore();

111. github.com/HanSolo/crac4

112. OK...BUT
HOW GOOD IS IT...?

113. Time to
fi
rst opera
ti
on
Spring-Boot
Micronaut
Quarkus
xml-transform
[ms]
0 1250 2500 3750 5000
4 352
980
1 001
3 898
OpenJDK

114. Time to
fi
rst opera
ti
on
Spring-Boot
Micronaut
Quarkus
xml-transform
[ms]
0 1250 2500 3750 5000
53
33
46
38
4 352
980
1 001
3 898
OpenJDK OpenJDK on CRaC

115. SUMMARY...

116. SUMMARY...
CRaC is a way to pause a JVM based application
And restore it at some point in the future
Bene
fi
t is potentially extremely fast time to full performance level
Eleminates the need for hotspot identi
fi
cation, method compiles,
recompiles and deoptimisations
Improved throughput from start
CRaC is an OpenJDK project
CRaC can save infrastructure cost

117. CPU
Utilization
0 %
25 %
50 %
75 %
100 %
Time
INFRASTRUCTURE COST
Checkpoint
JVM startup time
Interpretation +
Compilation Overhead
Start after restore
Eliminates startup time
Eliminates cpu overhead

118. github.com/CRaC

119. wiki.openjdk.org/display/crac

120. DEMO...

121. THANK
YOU