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TBT Blocking Budget

TBT Blocking Budget governs main thread blocking, shaping system behavior under specific failure modes and workloads.

performance

Definition

TBT Blocking Budget is a design property concerning main thread blocking. It defines how the system behaves under specific conditions — what guarantees hold, what trade-offs apply, and how the mechanism interacts with related techniques. The property is only meaningful when its preconditions are met; outside those conditions it provides no benefit and may add cost.

Context and scope

Apply TBT Blocking Budget when designing systems where main thread blocking matters. It is most useful under partial failure, high load, or correctness requirements. Pair it with observability to verify the claimed behavior in production. Do not assume the property holds without testing the specific configuration and workload.

Common misconceptions

  • TBT Blocking Budget eliminates all problems in its domain — it only bounds or shapes specific failure modes, not all pathologies.
  • TBT Blocking Budget is free once you adopt the right tool — the property depends on configuration, workload, and failure pattern, not the product label alone.

Anti-patterns

  • Enabling TBT Blocking Budget without measuring its cost in latency, availability, or operational complexity under production-like conditions.
  • Assuming TBT Blocking Budget composes safely with other guarantees — combining mechanisms can introduce new failure modes or negate benefits.

Related concepts

Authoritative source

https://web.dev/vitals/

What it is

TBT Blocking Budget is a design property concerning main thread blocking. It defines how the system behaves under specific conditions — what guarantees hold, what trade-offs apply, and how the mechanism interacts with related techniques. The property is only meaningful when its preconditions are met; outside those conditions it provides no benefit and may add cost.

When to use

Apply TBT Blocking Budget when designing systems where main thread blocking matters. It is most useful under partial failure, high load, or correctness requirements. Pair it with observability to verify the claimed behavior in production. Do not assume the property holds without testing the specific configuration and workload.

Common misconceptions

  • TBT Blocking Budget eliminates all problems in its domain — it only bounds or shapes specific failure modes, not all pathologies.
  • TBT Blocking Budget is free once you adopt the right tool — the property depends on configuration, workload, and failure pattern, not the product label alone.

Anti-patterns to avoid

  • Enabling TBT Blocking Budget without measuring its cost in latency, availability, or operational complexity under production-like conditions.
  • Assuming TBT Blocking Budget composes safely with other guarantees — combining mechanisms can introduce new failure modes or negate benefits.
  • Long Task Observer (longtask-observer)
  • Event Loop Starvation (event-loop-starvation)