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
34 lines
1.6 KiB
Plaintext
34 lines
1.6 KiB
Plaintext
==========================================================================
|
|
Page / region geometry as reported by THIS JVM
|
|
==========================================================================
|
|
max heap : 2,048 MB
|
|
UseG1GC / UseZGC : false / true
|
|
G1HeapRegionSize : 0 (ergonomic / not applicable)
|
|
=> ZGC small pages are 2 MB; objects up to 1/8 of a page (256 KB) use them.
|
|
Larger objects use a medium page, and anything bigger gets a Large page
|
|
of its own -- which ZGC frees rather than relocates.
|
|
|
|
ZGC internals flags visible in this JVM
|
|
ZFragmentationLimit = 5.0
|
|
ZCollectionIntervalMinor = -1.0
|
|
ZCollectionIntervalMajor = -1.0
|
|
ZAllocationSpikeTolerance = 2.0
|
|
ZUncommit = false
|
|
ZUncommitDelay = 300
|
|
SoftMaxHeapSize = 2,147,483,648 bytes (2048 MB)
|
|
|
|
ZGC pages actually allocated while creating the objects above
|
|
page type count total bytes
|
|
Large 2 25,165,824
|
|
Medium 1 33,554,432
|
|
|
|
Objects allocated in this run
|
|
65,536 bytes (64 KB) expect ZGC Small page (2 MB, shared with other objects)
|
|
262,144 bytes (256 KB) expect ZGC Medium page (shared; size is a range in JDK 25)
|
|
524,288 bytes (512 KB) expect ZGC Medium page (shared; size is a range in JDK 25)
|
|
2,097,152 bytes (2 MB) expect ZGC Medium page (shared; size is a range in JDK 25)
|
|
4,194,304 bytes (4 MB) expect ZGC Large page -- one page for this object, freed not relocated
|
|
16,777,216 bytes (16 MB) expect ZGC Large page -- one page for this object, freed not relocated
|
|
|
|
checksum: 6
|