bcquality/microsoft/knowledge/performance/use-findset-readonly-by-default.md

bc-version	domain	keywords	technologies	countries	application-area
all	performance	findset lock locktable readonly update	al	w1	all

Use FindSet in read-only mode by default

Description

FindSet has two modes: FindSet() and FindSet(false) are read-only and take no update lock; FindSet(true) sets update-lock read isolation on the record before fetching. Update locks are expensive and hold for the lock scope, so passing true when you do not intend to modify the records increases contention under load.

Best Practice

Call FindSet with no arguments when the loop only reads field values. Pass true only when the same loop is expected to call Modify, Delete, or Rename on the record, and the correctness of the operation depends on the matching rows being locked for the iteration.

See sample: use-findset-readonly-by-default.good.al.

Anti Pattern

Writing FindSet(true) reflexively for every iteration forces the platform to take a LockTable on every call, even when the loop only reads values. The older two-parameter signature FindSet(ForUpdate, UpdateKey) is obsolete and must not be used.

See sample: use-findset-readonly-by-default.bad.al.