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Pure git-mv relocation of all 7 performance articles from community/knowledge/performance/ to microsoft/knowledge/performance/. No content changes. Co-authored-by: Jesper Schulz-Wedde <jesper.schulzwedde@microsoft.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
28 lines
1.6 KiB
Markdown
28 lines
1.6 KiB
Markdown
---
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bc-version: [all]
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domain: performance
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keywords: [singleinstance, subscriber, event, memory, session]
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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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# Avoid growing globals in SingleInstance subscribers
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> Contributions welcome — open a PR to refine or extend this article.
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## Description
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A codeunit with `SingleInstance = true` is allocated once per session and lives until the session ends. Global variables on it are never collected between event fires. A subscriber that accumulates data into a global — buffering payloads, appending to a list, caching without a cap — steadily grows its session footprint for the entire user session. The symptom is memory that only recovers on sign-out, and it surfaces only on long-running sessions.
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## Best Practice
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Keep the global footprint on a SingleInstance subscriber bounded and intentional: a handful of flags, a setup record, a bounded cache with a maximum size. When cross-event state is genuinely needed, define an explicit reset point — end of a business process, arrival of a specific terminal event — that clears the growing collection.
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See sample: `avoid-growing-globals-in-singleinstance-subscribers.good.al`.
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## Anti Pattern
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A SingleInstance subscriber that appends each event's payload to a global list, dictionary, or temporary record without a cap or cleanup trigger. The list grows for hours, memory pressure builds quietly, and debugging the root cause on a live environment is substantially harder than noticing the unbounded append in code review.
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See sample: `avoid-growing-globals-in-singleinstance-subscribers.bad.al`.
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