mirror of
https://github.com/microsoft/BCQuality.git
synced 2026-08-06 09:26:52 +01:00
3f0b6a41db
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 667c64a8-eb36-4440-bc41-6a97d8fb5542
26 lines
1.5 KiB
Markdown
26 lines
1.5 KiB
Markdown
---
|
|
bc-version: [all]
|
|
domain: performance
|
|
keywords: [maintainsiftindex, sift, calcsums, flowfield, write-cost]
|
|
technologies: [al]
|
|
countries: [w1]
|
|
application-area: [all]
|
|
---
|
|
|
|
# Choose MaintainSIFTIndex by read-write ratio
|
|
|
|
> Contributions welcome — open a PR to refine or extend this article.
|
|
|
|
## Description
|
|
|
|
`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.
|
|
|
|
## Best Practice
|
|
|
|
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.
|
|
|
|
See sample: `choose-maintainsiftindex-by-read-write-ratio.good.al`.
|
|
|
|
## Anti Pattern
|
|
|
|
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.
|