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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>
28 lines
1.7 KiB
Markdown
28 lines
1.7 KiB
Markdown
---
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bc-version: [all]
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domain: performance
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keywords: [isempty, findset, extra-round-trip, existence-check, false-positive]
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technologies: [al]
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countries: [w1]
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application-area: [all]
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---
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# IsEmpty immediately before FindSet is an extra round-trip
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> Contributions welcome — open a PR to refine or extend this article.
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## Description
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`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.
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## Best Practice
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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.
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See sample: [`isempty-before-findset-is-extra-round-trip.good.al`](isempty-before-findset-is-extra-round-trip.good.al).
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## Anti Pattern
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`if not Rec.IsEmpty() then if Rec.FindSet() then repeat`. Also a false-positive review comment that asks to add that guard. The second read does not avoid the first; it duplicates it.
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See sample: [`isempty-before-findset-is-extra-round-trip.bad.al`](isempty-before-findset-is-extra-round-trip.bad.al).
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