Package org.openjdk.jmc.flightrecorder.rules.jdk.memory

Class StringDeduplicationRule

java.lang.Object

org.openjdk.jmc.flightrecorder.rules.AbstractRule

org.openjdk.jmc.flightrecorder.rules.jdk.memory.StringDeduplicationRule

All Implemented Interfaces:

IRule

public class StringDeduplicationRule
extends AbstractRule

Intent of this rule is to find out if it would be worth enabling string deduplication. String deduplication is available together with the G1 GC, see JEP 192. Rule looks at how much memory is used by the char/byte arrays used internally in strings, it also check the heap usage.

The rule can only give guidance, it is up to the user to measure changes memory consumption after enabling string deduplication. It can still be that the amount of memory used to hold metadata of the deduplicated strings is more than the saved heap space.

Rule uses the ObjectCount event if available, otherwise the TLAB events. Uncertainties in the calculations comes both from the statistical issues that the AllocationInNewTLAB event provides, and also from the fact that it is hard to know which of the char/byte arrays that actually are the internal string arrays. Looking at the allocation stack trace can help a bit, but allocations can be missed. If using the ObjectCount event, the statistics are better, but it is impossible to know which arrays to count.

Field Summary

Fields

Modifier and Type	Field	Description
static TypedResult<IQuantity>	HEAP_USAGE
static TypedResult<String>	INTERNAL_STRING_TYPE
static TypedResult<IQuantity>	STRING_HEAP_RATIO

Fields inherited from class org.openjdk.jmc.flightrecorder.rules.AbstractRule

evaluationTask

Constructor Summary

Constructors

Constructor	Description
StringDeduplicationRule()

Method Summary

Modifier and Type	Method	Description
protected IResult	getResult(IItemCollection items, IPreferenceValueProvider vp, IResultValueProvider rp)

Methods inherited from class org.openjdk.jmc.flightrecorder.rules.AbstractRule

createEvaluation, getConfigurationAttributes, getId, getName, getRequiredEvents, getResults, getTopic

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

HEAP_USAGE

public static final TypedResult<IQuantity> HEAP_USAGE

STRING_HEAP_RATIO

public static final TypedResult<IQuantity> STRING_HEAP_RATIO

INTERNAL_STRING_TYPE

public static final TypedResult<String> INTERNAL_STRING_TYPE

Constructor Detail

StringDeduplicationRule

public StringDeduplicationRule()

Method Detail

getResult

protected IResult getResult(IItemCollection items,
                            IPreferenceValueProvider vp,
                            IResultValueProvider rp)

Specified by:

getResult in class AbstractRule