Serial GC Tracing - Tenuring Threshold Controlled

This section provides a tutorial showing how to control Serial collector Tenuring threshold with InitialTenuringThreshold and MaxTenuringThreshold JVM options.

In previous tutorials, we learned that the Serial collector controls objects tenuring using the tenuring threshold (default is 15 age old). When a live object reaches the tenuring threshold age, it is considered as matured to be promoted to tenured generation.

But if the survivor space usage reaches the TargetSurvivorRatio (default is 50% used), all remaining live objects will be promoted to tenured generation regardless of their ages.

The Serial collector also dynamically adjust the tenuring threshold based on current survivor space usage.

If we give enough survivor space, live objects may stay in Young generation for a long time surviving up to 15 times of Minor GCs. This may have performance impact on your application. An object of age 15 means that it has been copied 15 times between the two survivor spaces ("from" and "to" spaces).

If we want to change the default behavior, we can use InitialTenuringThreshold and MaxTenuringThreshold JVM options:

Let's try it with our test program GarbageCollection2.java with fixed new generation size option of "-XX:NewSize=102m":

C:\herong>java -Xms105m -Xmx105m -XX:+UseSerialGC
   -XX:NewSize=102m -XX:SurvivorRatio=1
   -XX:TargetSurvivorRatio=99
   -XX:InitialTenuringThreshold=3 -XX:MaxTenuringThreshold=3
   -Xlog:gc=info,gc+heap=debug,gc+age=trace GarbageCollection2
...
108   75956224   7997424   67958800
[debug][gc,heap] GC(3) Heap before GC invocations=3 (full 0):
                        def new generation   total 68864K, used 66366K ...
[debug][gc,heap] GC(3)   eden space 34496K,  97% used [...
[debug][gc,heap] GC(3)   from space 34368K,  94% used [...
[debug][gc,heap] GC(3)   to   space 34368K,   0% used [...
[debug][gc,heap] GC(3)  tenured generation   total 5312K, used 0K ...
[debug][gc,heap] GC(3)    the space 5312K,   0% used [...

[debug][gc,age ] GC(3) Desired survivor size 34840896 bytes,
                       new threshold 3 (max threshold 3)
[trace][gc,age ] GC(3) Age table with threshold 3 (max threshold 3)
[trace][gc,age ] GC(3) - age   1:   24117752 bytes,   24117752 total
[trace][gc,age ] GC(3) - age   2:    4195104 bytes,   28312856 total
[trace][gc,age ] GC(3) - age   3:    3145776 bytes,   31458632 total

[info ][gc,heap] GC(3) DefNew: 66366K->30721K(68864K)
[info ][gc,heap] GC(3) Tenured: 0K->2876K(5312K)
[info ][gc     ] GC(3) Pause Young (Allocation Failure)
                       64M->32M(72M) 12.245ms

[debug][gc,heap] GC(3) Heap after GC invocations=4 (full 0):
                        def new generation   total 68864K, used 30721K ...
[debug][gc,heap] GC(3)   eden space 34496K,   0% used [...
[debug][gc,heap] GC(3)   from space 34368K,  89% used [...
[debug][gc,heap] GC(3)   to   space 34368K,   0% used [...
[debug][gc,heap] GC(3)  tenured generation   total 5312K, used 2876K ...
[debug][gc,heap] GC(3)    the space 5312K,  54% used [...

As you can see from the output, Minor GC #4 promoted 2876K objects to tenured generation, because the maximum tenuring threshold was set to 3. Those objects would grow to age 4, if left in the survivor space.

Table of Contents

 About This Book

 Heap Memory Area and Size Control

 JVM Garbage Collection Logging

 Introduction of Garbage Collectors

Serial Collector - "+XX:+UseSerialGC"

 What Is Serial Collector

 GC Log Message Format for Serial Collector

 GC Log Message Examples of Serial Collector

 Log Message Types from Serial Collector

 Serial Collector Stops Application for Minor/Major GC

 Usage Report on Heap Memory Areas

 Default NewRatio - Old vs. New Generation

 "-XX:NewRatio" - Ratio of Tenured and "new" Generation

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

 Serial GC Tracing - Tight Heap

 Serial GC Tracing - Tight Heap (Part 2)

 Serial GC Tracing - Tight Heap (Part 3)

 Serial GC Tracing - Plenty of Heap

 Serial GC Tracing - Aged Live Objects

 Serial GC Tracing - Tenuring Threshold

 "-XX:TargetSurvivorRatio" - Second Tenuring Condition

Serial GC Tracing - Tenuring Threshold Controlled

 "-XX:+NeverTenure" and "-XX:+AlwaysTenure" Working

 Minor GC Triggering Condition of Serial Collector

 Parallel Collector - "+XX:+UseParallelGC"

 Concurrent Mark-Sweep (CMS) Collector - "+XX:+UseConcMarkSweepGC"

 Garbage First (G1) Collector - "+XX:+UseG1GC"

 The Z Garbage Collector (ZGC) - "+XX:+UseZGC"

 Object References and Garbage Collection

 Garbage Collection Performance Test Program

 Performance Tests on Serial Collector

 Performance Tests on Parallel collector

 Performance Tests on Concurrent collector

 Performance Tests on G1 collector

 Garbage Collection Performance Test Summary

 References

 Full Version in PDF/EPUB