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Spring Boot startup time: bean-by-bean diagnosis, and one directory per post

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Adds spring-boot-startup-time/, the companion project for BLOG-618: a runnable
Spring Boot 4.1.1 application on JDK 25 that installs BufferingApplicationStartup
and FlightRecorderApplicationStartup behind a system property, and a /diag/startup
endpoint that computes step self time -- the number /actuator/startup does not give
you and the one that names the actual culprits.

Captured under docs/output/: the step tree sorted both ways, the same startup as JFR
events, a +5000-class experiment putting 0.11 ms per scanned class on the classpath
scan tax, the silent truncation a 2048-step buffer performs, and JDK 25 AOT cache
timings (6.93 s to 4.82 s). Post body and metadata live in post/.

Moves the existing Actuator project into actuator-in-production/ so the repository
holds one directory per article; the root README is now an index.
This commit is contained in:
Ankur Mhatre
2026-09-04 23:58:38 +05:30
parent 4b6cefa60a
commit 958b401f0f
112 changed files with 2744 additions and 154 deletions
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spring-boot-startup-time/post/images/02-buffer-truncation.svg Normal file
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<?xml version="1.0" encoding="UTF-8"?>
<svg viewBox="0 0 740 250" role="img" aria-label="Diagram of a truncated startup buffer. The full timeline nests spring.context.refresh around configuration parsing and five thousand four hundred bean instantiations, ending with application started and ready. With a capacity of two thousand and forty-eight the buffer keeps the first two thousand and forty-eight steps to finish, all inner leaves, and silently drops spring.context.refresh, application started and application ready, because those steps end last." xmlns="http://www.w3.org/2000/svg">
<style>
.t{font:600 13px system-ui,sans-serif;fill:#2b3138}
.h{font:600 11px system-ui,sans-serif;fill:#57606b}
.m{font:11px ui-monospace,Menlo,monospace;fill:#2b3138}
.c{font:11px system-ui,sans-serif;fill:#57606b}
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<text class="t" x="12" y="18">What a 2048-step buffer keeps, and what it throws away</text>
<text class="h" x="12" y="42">STEPS, IN THE ORDER THEY END →</text>
<rect x="12" y="52" width="470" height="24" fill="#e7f4ea" stroke="#4a9d63"/>
<text class="m" x="20" y="68">2048 leaf steps: spring.beans.instantiate bulk1 … bulk2718</text>
<rect x="482" y="52" width="246" height="24" fill="#f4f5f7" stroke="#b7bec9" stroke-dasharray="3 3"/>
<text class="m" x="490" y="68">3352 more instantiate steps — dropped</text>
<rect x="482" y="84" width="246" height="24" fill="#f7d9d3" stroke="#c56a54" stroke-dasharray="3 3"/>
<text class="m" x="490" y="100">spring.context.refresh — dropped</text>
<rect x="482" y="116" width="246" height="24" fill="#f7d9d3" stroke="#c56a54" stroke-dasharray="3 3"/>
<text class="m" x="490" y="132">application.started / ready — dropped</text>
<line x1="482" y1="46" x2="482" y2="146" stroke="#c56a54" stroke-width="2"/>
<text class="h" x="488" y="44" fill="#c56a54">capacity reached</text>
<text class="c" x="12" y="176">The outermost steps end last, so they are the first casualties. Self-time arithmetic is now missing its outer frame,</text>
<text class="c" x="12" y="194">and the “whole refresh took N” figure is simply not in the data — while the endpoint still answers 200.</text>
<text class="c" x="12" y="218">The capacity counts steps, not beans. 16384 costs a few megabytes that are freed on the first drain. Pick the large number.</text>
</svg>
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