Answer
Tier 0 emits fast, minimally optimized code. Tier 1 recompiles hot methods with optimizations.
Tiered PGO improves performance for long-running APIs.
Quick Answer
Tiered compilation runs methods at Tier 0 first with minimal optimization for fast startup. As methods get called repeatedly (hot paths), the JIT recompiles them at Tier 1 with full optimizations. With PGO (Profile-Guided Optimization), it uses actual runtime data to make even smarter optimization decisions.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ