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Add BC performance knowledge from OptimAL learnings (#198)

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* Add BC performance knowledge from OptimAL learnings

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Address review feedback on performance guidance

Clarify predicate-supporting keys versus covering queries, demonstrate proven cache reuse, and evaluate the updated partial-load and bulk-update rules.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Jesper Schulz-Wedde <jesper.schulzwedde@microsoft.com>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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Jesper Schulz-Wedde 2026-09-29 17:21:28 +02:00 • committed by GitHub
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microsoft/knowledge/performance/isempty-before-findset-is-extra-round-trip.md
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@ -13,11 +13,11 @@ application-area: [all]
## Description
`IsEmpty` is the right API when the caller only needs existence — see `microsoft/knowledge/performance/use-isempty-for-existence-check.md`. It is not a cheap guard in front of a loop that will `FindSet` anyway. Both calls hit the database; `FindSet` already returns false when the filter matches nothing. Agents and reviewers often insert `if not Rec.IsEmpty() then` "for performance" and pay a second query for a result the iterator already provides.
`IsEmpty` is the right API when the caller only needs existence — see `microsoft/knowledge/performance/use-isempty-for-existence-check.md`. It is not a cheap guard in front of a loop that will `FindSet` anyway. `FindSet` already returns false when the filter matches nothing; an extra `IsEmpty` is unnecessary AL work and can issue a second database request, depending on caching. Agents and reviewers often insert `if not Rec.IsEmpty() then` "for performance" and duplicate a result the iterator already provides.
## Best Practice
When the body iterates, open with `if Rec.FindSet() then repeat ... until Next() = 0`. Do not flag a bare `FindSet` loop as missing an `IsEmpty` precondition. Reserve `IsEmpty` for branches that never materialize the row set.
When the body iterates, open with `if Rec.FindSet() then repeat ... until Next() = 0`. Do not flag a bare `FindSet` loop as missing an `IsEmpty` precondition. Reserve `IsEmpty` for branches that never materialize the row set. An early check before a *bulk write* or lock is a different, workload-dependent decision: it can help when the filtered set is usually empty, but adds work when rows exist and does not lock the set against change.
See sample: [`isempty-before-findset-is-extra-round-trip.good.al`](isempty-before-findset-is-extra-round-trip.good.al).