asmhatreandClaude Sonnet 5
2f88734f5d
MaxRAMPercentage vs a hardcoded -Xmx, -XX:-UseContainerSupport, the ActiveProcessorCount lie, and which diagnostic flags are worth leaving on in prod, verified in real Docker containers on JDK 25 and JDK 27. Co-Authored-By: Claude Sonnet 5 <[email protected]>
28 lines
1.6 KiB
Plaintext
28 lines
1.6 KiB
Plaintext
$ docker run -d --memory=1g --name hdr -v $PWD/docker/headersize.jar:/headersize.jar \
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--entrypoint java flags-demo:<tag> [extra flags] -cp /headersize.jar HeaderSizeDemo 2000000
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$ docker exec hdr jcmd 1 GC.class_histogram | grep -E "Pair|Total"
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--- JDK 25, default (UseCompactObjectHeaders=false), flags-demo:jdk25-jdk ---
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1: 2000000 48000000 HeaderSizeDemo$Pair
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273: 1 24 java.lang.invoke.StringConcatFactory$InlineHiddenClassStrategy$MethodHandlePair ([email protected])
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Total 2030279 57368512
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--- JDK 25, -XX:+UseCompactObjectHeaders ---
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1: 2000000 32000000 HeaderSizeDemo$Pair
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300: 1 16 java.lang.invoke.StringConcatFactory$InlineHiddenClassStrategy$MethodHandlePair ([email protected])
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Total 2030283 41272056
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--- JDK 27, default (UseCompactObjectHeaders=true), flags-demo:jdk27 ---
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1: 2000000 32000000 HeaderSizeDemo$Pair
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317: 1 16 java.lang.invoke.StringConcatFactory$InlineHiddenClassStrategy$MethodHandlePair (java.base@27)
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Total 2030937 41320144
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--- JDK 27, -XX:-UseCompactObjectHeaders ---
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1: 2000000 48000000 HeaderSizeDemo$Pair
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282: 1 24 java.lang.invoke.StringConcatFactory$InlineHiddenClassStrategy$MethodHandlePair (java.base@27)
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Total 2031092 57425040
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2,000,000 instances of a 2-int object: 48,000,000 bytes (24 bytes each) with the old header,
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32,000,000 bytes (16 bytes each) compact. 33% smaller per instance, reproduced symmetrically
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in both directions on both JDKs.
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