Class 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 Detail

      • STRING_FILTER

        private static final IItemFilter STRING_FILTER
      • STRING_ARRAY_ALLOCATION_FRAMES

        private static final TypedPreference<java.lang.String> STRING_ARRAY_ALLOCATION_FRAMES
      • STRING_ARRAY_LIVESET_RATIO_AND_HEAP_USAGE_LIMIT

        private static final TypedPreference<IQuantity> STRING_ARRAY_LIVESET_RATIO_AND_HEAP_USAGE_LIMIT
      • STRING_ARRAY_ALLOCATION_RATIO_AND_HEAP_USAGE_LIMIT

        private static final TypedPreference<IQuantity> STRING_ARRAY_ALLOCATION_RATIO_AND_HEAP_USAGE_LIMIT
    • Constructor Detail

      • StringDeduplicationRule

        public StringDeduplicationRule()
    • Method Detail

      • getLivesetRatioResult

        private Result getLivesetRatioResult​(IItemCollection items,
                                             java.lang.String stringInternalArrayType,
                                             IItemFilter stringInternalArrayTypeFilter,
                                             IQuantity averageStringSize,
                                             IQuantity stringLivesetRatioAndHeapUsageLimit,
                                             java.lang.String objectCountEventType,
                                             java.lang.String heapInfo,
                                             double heapUsedRatio,
                                             java.lang.String extraGcInfo)
      • getAllocationRatioResult

        private Result getAllocationRatioResult​(IItemCollection items,
                                                java.lang.String stringInternalArrayType,
                                                IItemFilter stringInternalArrayTypeFilter,
                                                IQuantity stringAllocationRatioLimit,
                                                java.lang.String allocationFramesString,
                                                java.lang.String heapInfo,
                                                double heapUsedRatio,
                                                java.lang.String extraGcInfo)
      • getAllocationFramesFilter

        private IItemFilter getAllocationFramesFilter​(java.lang.String allocationFramesString)