"-XX:SurvivorRatio" - Ratio of Eden and Survivor Space

Java GC Tutorials - Herong's Tutorial Examples

∟"-XX:SurvivorRatio" - Ratio of Eden and Survivor Space

This section describes the default 'new' ratio (size ratio of tenured vs. 'new' generation).

Can we also control the ratio between "eden" space and survivor spaces? The answer is yes, by using the "-XX:SurvivorRatio" JVM option.

The ratio between "eden" space and survivor spaces is defined as "SurvivorRatio", which is the ratio of the "eden" space and one survivor space.

By default, the "SurvivorRatio" is set to about 8. You can verify this with test results listed in previous tutorials.

Below is another test with "-Xms20m -Xmx20m -XX:NewRatio=1 -XX:SurvivorRatio=6" options. The "new" generation should get 10 MB, which will be divided into: Eden space of 7.5 MB, "from" Survivor space of 1.25 MB and "to" Survivor space of 1.25 MB:

herong> java -Xms20m -Xmx20m -XX:NewRatio=1 -XX:SurvivorRatio=6 \
   -XX:+UseSerialGC -Xlog:gc+heap=info GarbageCollection
...
[debug][gc,heap] GC(0) Heap after GC invocations=1 (full 0):
                        def new generation   total 8960K, used 1279K [...
[debug][gc,heap] GC(0)   eden space 7680K,   0% used [...
[debug][gc,heap] GC(0)   from space 1280K,  99% used [...
[debug][gc,heap] GC(0)   to   space 1280K,   0% used [...
[debug][gc,heap] GC(0)  tenured generation   total 10240K, used 1590K [...
[debug][gc,heap] GC(0)    the space 10240K,  15% used [...