LATENCY & PERFORMANCEAI SRE

Prefill vs Decode

Prefill processes the input context; decode generates output tokens one step at a time.

WHY IT MATTERS

Large prompts primarily hurt prefill and TTFT, while long outputs primarily stress decode capacity.

PRODUCTION EXAMPLE

A 60k-token context causes high TTFT even though the generated answer is only 200 tokens.

SRE DECISION

Is the workload prompt-heavy, output-heavy or mixed, and does capacity planning reflect that?

REMEMBERInput size and output size stress different parts of inference.
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