Class StringDeduplicationRule
- java.lang.Object
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- org.openjdk.jmc.flightrecorder.rules.AbstractRule
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- org.openjdk.jmc.flightrecorder.rules.jdk.memory.StringDeduplicationRule
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- 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.
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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
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Fields inherited from class org.openjdk.jmc.flightrecorder.rules.AbstractRule
evaluationTask
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Constructor Summary
Constructors Constructor Description StringDeduplicationRule()
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description protected IResult
getResult(IItemCollection items, IPreferenceValueProvider vp, IResultValueProvider rp)
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Methods inherited from class org.openjdk.jmc.flightrecorder.rules.AbstractRule
createEvaluation, getConfigurationAttributes, getId, getName, getRequiredEvents, getResults, getTopic
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Field Detail
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HEAP_USAGE
public static final TypedResult<IQuantity> HEAP_USAGE
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STRING_HEAP_RATIO
public static final TypedResult<IQuantity> STRING_HEAP_RATIO
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INTERNAL_STRING_TYPE
public static final TypedResult<String> INTERNAL_STRING_TYPE
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Method Detail
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getResult
protected IResult getResult(IItemCollection items, IPreferenceValueProvider vp, IResultValueProvider rp)
- Specified by:
getResult
in classAbstractRule
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