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Pause-less Garbage Collection with Java on IBM Z

General Page

The Java runtime supports a built-in memory manager that tracks an application’s usage of the Java heap. Garbage Collection (GC) is a process that is triggered when the heap becomes exhausted.
Overview
The Java runtime supports a built-in memory manager that tracks an application’s usage of the Java heap. Garbage Collection (GC) is a process that is triggered when the heap becomes exhausted. During the GC process, the application is stalled in “stop-the-world” phases, to allow GC to identify and reclaim memory from Java objects that are no longer referenced. Untuned, such “stop-the-world” GC phases can have a detrimental impact to your application’s throughput and response time.

Pause-less Garbage Collection (GC) is a new GC mode in the 64-bit IBM SDK for Java, aimed to reduce the impact of GC “stop-the-world” phases, and improve the throughput and consistency of response-times for Java applications. This technology leverages the new Guarded Storage Facility introduced in IBM z14 hardware, to allow more parallel execution of GC-related processing with application code. Pause-less Garbage Collection is particularly relevant for applications with strict response-time Service Level Agreements (SLAs) and/or large Java heaps.
How To Enable
Please see the Requirements section below for the prerequisite hardware and software levels to support Pause-less Garbage Collection. The Pause-less GC mode is not enabled by default. To enable the new Pause-less GC mode in your application, please introduce -Xgc:concurrentScavenge to the JVM options.
To verify that Pause-less GC is enabled correctly, collect a verbose GC diagnostic with:
   
      java -verbose:gc –version
And confirm the following attribute is set to true:
      <attribute name=”concurrentScavenger” value=”true” />
Requirements
  • IBM Java 8.0.5.0 (Java 8 SR5) or newer (64-bit)
  • IBM z14 or newer with the Guarded Storage Facility enabled
  • z/OS 2.3 or z/OS 2.2 with APAR OA51643
  • z/VM 6.4 or newer
Availability
The pause-less GC mode is currently only available on 64-bit IBM SDK for z/OS.
Linux kernel support has been up streamed and awaiting Linux distribution adoption.
Learn more
For more information about Pause-less GC please visit the following:

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Document Information

Modified date:
10 February 2022

UID

ibm16320797