Ankur
e189da79ba
Complete companion suite for the ankurm.com guide. Everything was compiled and
executed on java 25.0.3+9-LTS-195 (AMD Ryzen 5 5600U, Windows 11); every file
under results/ is unedited program output.
Code
latency/ open-loop latency harness that measures from intended arrival, so
coordinated omission is accounted for rather than hidden. Reports
response time and service time side by side; the gap reached 2910x
on G1.
jmh/ four microbenchmarks isolating one mechanism each: TLAB allocation,
the ZGC load barrier (with a primitive-load control), the write
barrier (with null / old-to-old / primitive controls), and promotion
pressure.
tuning/ provokes ZGC allocation stalls and reads its own JFR recording back,
grouped by page class. jdk.ZAllocationStall is enabled without a
threshold, because the 10 ms default hides most stalls.
internals/ ZGC page classes vs G1 humongous, read from the live VM via
HotSpotDiagnosticMXBean and jdk.ZPageAllocation events.
analysis/ unified GC log parser that keeps stop-the-world pauses and
concurrent phases in separate buckets.
env/ environment capture; proves generational mode from JMX bean names.
Docs
Eight chapters covering the JEP 439/474/490 timeline, colored pointers and both
barriers, allocation stalls, a full flag reference, logging and JFR, benchmark
methodology, corner cases, and a decision procedure.
Headline result (60 s, 20k req/s, 2 GB heap, ~585 MB live)
p50 ZGC 0.006 ms G1 0.005 ms
p99.9 ZGC 1.437 ms G1 95.169 ms
total STW time ZGC 1.503 ms G1 1,139.624 ms
37 lines
1.6 KiB
Plaintext
37 lines
1.6 KiB
Plaintext
==============================================================================
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GC log analysis: zgc-latency.log
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==============================================================================
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lines parsed : 2,247
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young / minor cycles : 45
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old / major cycles : 17
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ZGC allocation stalls : 40
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G1 evacuation failures : 0
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full GCs : 0
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STOP-THE-WORLD PAUSES (this is application freeze time)
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count : 106
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total : 1.503 ms
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mean : 0.014 ms
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p50 : 0.014 ms
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p99 : 0.044 ms
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max : 0.054 ms
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by phase
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Pause Mark Start (Major) n=8 total= 0.139 ms max= 0.021 ms
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Pause Mark End n=38 total= 0.683 ms max= 0.044 ms
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Pause Relocate Start n=38 total= 0.330 ms max= 0.021 ms
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Pause Mark Start n=22 total= 0.351 ms max= 0.054 ms
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CONCURRENT PHASES (application keeps running -- NOT freeze time)
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Concurrent Mark n=38 total= 894.499 ms max= 78.403 ms
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Concurrent Mark Free n=38 total= 0.097 ms max= 0.033 ms
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Concurrent Reset Relocation Set n=38 total= 4.331 ms max= 0.934 ms
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Concurrent Select Relocation Set n=38 total= 48.991 ms max= 5.372 ms
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Concurrent Relocate n=38 total=1092.392 ms max=151.380 ms
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Concurrent Process Non n=8 total= 5.635 ms max= 0.984 ms
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Concurrent Remap Roots n=8 total= 10.919 ms max= 2.207 ms
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Adding the block above to the pause block would be a category error:
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concurrent time overlaps application execution by design.
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