out-of-memory-behavior-588cfd9.md

Out-Of-Memory Behavior

SAP Java Buildpack prints a histogram of the heap memory to the logs when the JVM encounters a terminal failure.

Output Code:

ERR Stopping VM due to OutOfMemoryError
ERR Resource exhaustion event: the JVM was unable to allocate memory from the heap.
ERR ResourceExhausted! (1/0)
OUT | Instance Count | Total Bytes | Class Name                                    |
OUT | 30130          | 5556616     | [C                                            |
OUT | 866            | 2485600     | [B                                            |
OUT | 29215          | 701160      | Ljava/lang/String;                            |
OUT | 3971           | 449528      | Ljava/lang/Class;                             |
OUT | 9998           | 319936      | Ljava/util/HashMap$Node;                      |
OUT | 3624           | 318912      | Ljava/lang/reflect/Method;                    |
OUT | 6429           | 205728      | Ljava/util/concurrent/ConcurrentHashMap$Node; |
OUT | 2821           | 171472      | [Ljava/lang/Object;                           |
OUT | 40             | 117328      | [J                                            |
OUT | 750            | 111096      | [Ljava/util/HashMap$Node;                     |
OUT | 5618           | 89888       | Ljava/lang/Object;                            |
OUT | 1054           | 74048       | [Ljava/lang/String;                           |
OUT | 696            | 62552       | [I                                            |
OUT | 59             | 51920       | [Ljava/util/concurrent/ConcurrentHashMap$Node;|
OUT | 1063           | 51024       | Ljava/util/HashMap;                           |
OUT | 854            | 40992       | Lorg/apache/tomcat/util/modeler/AttributeInfo;|
...
 

This functionality is activated by default.

If you want to deactivate it, add property -XX:+ExitVMOnOutOfMemoryError through the JBP_CONFIG_JAVA_OPTS property in the application's manifest.yml file, like this:

---
applications:
- name: <APP_NAME>
  buildpacks:
  - sap_jakarta_buildpack
  env:
    JBP_CONFIG_JAVA_OPTS: 'false, java_opts: ''-XX:+ExitVMOnOutOfMemoryError'''
  ...

Killing a process with jvmkill

SAP Java Buildpack allows you to set jvmkill agent when staging your application. A jvmkill agent is added by default to the properties when starting the Java application process. The following configuration is added:

-agentpath:META-INF/.sap_java_buildpack/jvm_kill/jvmkill-<jvmkill_version>.RELEASE-trusty.so=printHeapHistogram=1

This is sufficient to print a histogram and kill the process when an out-of-memory (OOM) error occurs.

If you want to disable jvmkill and omit its agent being added to the startup properties, use the SJB_NO_JVMKILL environment variable, like this:

env:
  SJB_NO_JVMKILL: true

Generate Heap Dumps with Java Properties

It's a good practice to generate a .hprof heap dump file on the event of OutOfMemoryError to analyze and find the root cause of the issue.

Various distributions including SapMachineJre and SapMachineJdk provide standard mechanism for generating a heap dump in the event of an OOM error. The following properties can be added on startup for this purpose:

-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=<heap_dump_path> -XX:OnOutOfMemoryError='kill -9 %p'

• -XX:+HeapDumpOnOutOfMemoryError triggers heap dump generation under a default path.

• -XX:HeapDumpPath specifies where to specify the heap dump file.

• -XX:OnOutOfMemoryError specifies what command or script to be run if OOM occurs. This command usually kills the process.

The heap dump is generated and stored in an application container location. This means, it will be removed once the application instance container is restarted.

Note:

Killing the process will trigger a restart. Therefore, if you need to investigate further in the heap dump file stored in the application container, the process should not be killed.

Related Information

ActiveProcessorCount

Cloud Foundry: jvmkill