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Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 667c64a8-eb36-4440-bc41-6a97d8fb5542 Co-authored-by: Jesper Schulz-Wedde <jesper.schulzwedde@microsoft.com>
26 lines
1.5 KiB
Markdown
26 lines
1.5 KiB
Markdown
---
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bc-version: [all]
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domain: performance
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keywords: [maintainsiftindex, sift, calcsums, flowfield, write-cost]
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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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# Choose MaintainSIFTIndex by read-write ratio
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> Contributions welcome — open a PR to refine or extend this article.
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## Description
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`MaintainSIFTIndex` on a key decides whether SQL Server maintains the SIFT indexed view as underlying rows change. With `Yes`, writes that affect the key or sum fields also maintain the indexed aggregate. With `No`, that SIFT indexed view is not maintained, so a compatible `CalcSums` or FlowField calculation is computed from the base table instead and may require scanning many rows. There is no deferred "first read rebuild" of the SIFT structure.
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## Best Practice
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Measure aggregate-read latency and write cost under realistic filters and volumes. Keep `MaintainSIFTIndex = true` when the maintained aggregate materially benefits frequent `CalcSums` or FlowField reads. Consider `false` when writes dominate and the less-frequent aggregate reads can tolerate calculation from the base table.
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See sample: `choose-maintainsiftindex-by-read-write-ratio.good.al`.
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## Anti Pattern
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Leaving `MaintainSIFTIndex = Yes` on every key by reflex or convenience. On write-heavy tables the cumulative cost turns every INSERT or MODIFY into several additional aggregate updates, and the impact compounds in batch imports and posting routines — often without any code-review signal that the property is the cause.
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