Keep your API fast—even at peak

Each labeled box is a separate execution environment. A reused environment can sometimes retain local history between requests, but those local records are not automatically shared with the other environments.

C illustrates a new environment with an empty history while A and B have their own past observations. Missing measurements do not establish that the shared database is healthy or has spare capacity.

For the following possible failure pattern, consider environments whose histories retain old fast observations. Their earlier experience is evidence about the past, not a direct measurement of the shared database’s current pressure.

Follow the three work routes into the same database. A, B, and C still have old fast evidence when admitting this burst; slow results from the newly admitted work have not returned yet.

Each returned result can update its originating environment’s local history. That result is delayed feedback about work already admitted; whether it changes the guard’s signal depends on eligibility and history rules.

The new evidence comes from an operation admitted earlier. A client cannot use that operation’s final duration before the measurement finishes. Sharing evidence later does not remove this causal delay.

Here the eligible histories cause the local guards to refuse new protected work. No new work routes reach the database. This is a possible branch, not a claim that every slow observation necessarily trips every guard.

While these clients skip protected work, they produce few new completions to measure. Existing work may still return results, but a refusal itself is not a new database latency observation.

The old observations stop qualifying under the history rules. That leaves too little current evidence in this illustrative branch. A history aging out does not itself make the database faster or add processing capacity.

Follow the work routes returning together: the histories are empty, not freshly measured fast. Optimistic reopening can admit another combined burst before useful current evidence has accumulated.

Each row is one environment and each column is a stage, not a measured time interval. The matching shapes show a possible synchronized pattern: a burst, common refusal, and another burst instead of settling.

The arrows now represent reports and admission checks, not database query traffic. A, B, and C contribute to and consult the same intended shared observation scope; they no longer rely only on their separate private past.

Sharing reduces fragmented histories but does not guarantee stable control or remove delayed feedback. Freshness rules, bounded work, and careful recovery remain necessary; there is deliberately no promised flat healthy throughput line here.