Update GC tuning guide with new default values for G1HeapWastePercent and G1MixedGCLiveThresholdPercent

Alert status: Fixed

Documentation Updated: http://st-doc.us.oracle.com/review/rsb/html/E51587_02/g1_gc_tuning.htm#g1_gc_tuning

Scope: Small

Engineering has provided enough information for this task. Updating the GC Tuning Guide is easy with these default values.

However, these options should be moved to the Java man page; a new bug has been opened for this; see JDK-8060484.

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The GC tuning guide:

http://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/g1_gc_tuning.html#important_defaults

mentions the two flags G1HeapWastePercent and G1MixedGCLiveThresholdPercent. In 8u40 these flags got new default values when JDK-8059452 was fixed.

The tuning guide says:

"-XX:G1MixedGCLiveThresholdPercent=65

Sets the occupancy threshold for an old region to be included in a mixed garbage collection cycle. The default occupancy is 65 percent.Footref1

This is an experimental flag. See How to Unlock Experimental VM Flags for an example. This setting replaces the -XX:G1OldCSetRegionLiveThresholdPercent setting."

The default value has been changed from 65 to 85. So, all that needs to be done is to replace the two occurrences of 65 with 85 in the text above.



"-XX:G1HeapWastePercent=10

Sets the percentage of heap that you are willing to waste. The Java HotSpot VM does not initiate the mixed garbage collection cycle when the reclaimable percentage is less than the heap waste percentage. The default is 10 percent.Footref1"


The default value has been changed from 10 to 5. So, all that needs to be done is to replace the two occurrences of 10 with 5 in the text above.