How do you reason about garbage-collection latency, throughput, and tuning?

Frames collector and heap decisions around service goals, workload evidence, pause distributions, live set, and deployment limits.

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TL;DR

Throughput collectors prioritize total application work, while low-pause collectors spend more resources to keep individual pauses shorter. Heap size affects both headroom and collection behavior: too small creates frequent pressure, while unnecessarily large heaps consume capacity and can lengthen some work. I start from latency objectives, throughput, allocation rate, live set, and deployment memory limits. The collector and settings follow those requirements.

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Proportionate GC judgment without cargo-cult flags or collector trivia.

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Core answer
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Overview
GC tuning is a service-level trade-off among pause time, throughput, memory footprint, and operational predictability.
Throughput collectors prioritize total application work, while low-pause collectors spend more resources to keep individual pauses shorter. Heap size affects both headroom and collection behavior: too small creates frequent pressure, while unnecessarily large heaps consume capacity and can lengthen some work. I start from latency objectives, throughput, allocation rate, live set, and deployment memory limits. The collector and settings follow those requirements.
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Stronger answer
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I inspect pause percentiles and causes, concurrent-cycle behavior, allocation stalls, CPU, and post-GC occupancy under representative load. A latency problem caused by an unbounded cache or bursty allocation is not solved reliably by switching collectors. Defaults in a modern supported JDK are a reasonable baseline, and one change at a time makes results interpretable. The synthetic baseline includes warm-up and the same container CPU and memory constraints as production.

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Details

Copying GC flags from an unrelated service.
Optimizing average pause only.
Changing collector and application behavior simultaneously.

How do you reason about garbage-collection latency, throughput, and tuning?

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