Add per-row performance guidance

Document SetAutoCalcFields for per-row FlowFields and direct writes on iterated records, with focused reviewer retrieval cues.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 85be3fc4-5253-47b8-ba1b-6b8fd188fcea

microsoft/knowledge/performance/avoid-cloning-records-before-modify-delete-in-loops.bad.al

@@ -0,0 +1,19 @@
+codeunit 50493 "Perf Record Clone Bad"
+{
+    procedure IncreaseCustomerCreditLimits(Percent: Decimal)
+    var
+        Customer: Record Customer;
+        CustomerCopy: Record Customer;
+    begin
+        Customer.SetLoadFields("Credit Limit (LCY)");
+        Customer.SetFilter("Credit Limit (LCY)", '>0');
+        if Customer.FindSet(true) then
+            repeat
+                CustomerCopy.Copy(Customer);
+                CustomerCopy.Validate(
+                    "Credit Limit (LCY)",
+                    Round(CustomerCopy."Credit Limit (LCY)" * (1 + Percent / 100)));
+                CustomerCopy.Modify(true);
+            until Customer.Next() = 0;
+    end;
+}

microsoft/knowledge/performance/avoid-cloning-records-before-modify-delete-in-loops.good.al

@@ -0,0 +1,17 @@
+codeunit 50492 "Perf Record Clone Good"
+{
+    procedure IncreaseCustomerCreditLimits(Percent: Decimal)
+    var
+        Customer: Record Customer;
+    begin
+        Customer.SetLoadFields("Credit Limit (LCY)");
+        Customer.SetFilter("Credit Limit (LCY)", '>0');
+        if Customer.FindSet(true) then
+            repeat
+                Customer.Validate(
+                    "Credit Limit (LCY)",
+                    Round(Customer."Credit Limit (LCY)" * (1 + Percent / 100)));
+                Customer.Modify(true);
+            until Customer.Next() = 0;
+    end;
+}

microsoft/knowledge/performance/avoid-cloning-records-before-modify-delete-in-loops.md

@@ -0,0 +1,26 @@
+---
+bc-version: [all]
+domain: performance
+keywords: [clone, copy, recordref, gettable, by-value, modify, delete, loop]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Avoid cloning records before Modify or Delete in loops
+
+## Description
+
+Microsoft's [AL database-method performance guidance](https://learn.microsoft.com/en-us/dynamics365/business-central/dev-itpro/administration/optimize-sql-al-database-methods-and-performance-on-server#insert-modify-delete-and-locktable) states that cloning an iterated record before `Modify` or `Delete` restarts the SQL `SELECT` and issues an extra SQL statement for every row. The runtime treats `Record.Copy`, `RecordRef.GetTable`, and passing a record by value to a writing helper as clones in this situation.
+
+## Best Practice
+
+Use `FindSet(true)` when the loop writes the traversed rows, and call `Modify` or `Delete` on that iterating record variable. If generic code is required, open and iterate the `RecordRef` directly instead of calling `GetTable` for each typed record. Keep a per-row loop when validation or row-specific behavior is required; this rule does not imply that `ModifyAll` or `DeleteAll` is equivalent.
+
+See sample: `avoid-cloning-records-before-modify-delete-in-loops.good.al`.
+
+## Anti Pattern
+
+Inside an active traversal, copy the current row, convert it with `RecordRef.GetTable`, or pass it without `var` to a helper, then call `Modify` or `Delete` on that clone. Do not flag read-only snapshots, temporary records, or copies used to write a different target table; the documented extra-statement concern is clone-before-write on the traversed table.
+
+See sample: `avoid-cloning-records-before-modify-delete-in-loops.bad.al`.

microsoft/knowledge/performance/use-setautocalcfields-for-per-row-flowfields.bad.al

@@ -0,0 +1,16 @@
+codeunit 50491 "Perf AutoCalcFields Bad"
+{
+    procedure CollectOverLimitCustomers(var CustomerNos: List of [Code[20]])
+    var
+        Customer: Record Customer;
+    begin
+        Customer.SetLoadFields("Credit Limit (LCY)");
+        Customer.SetFilter("Credit Limit (LCY)", '>0');
+        if Customer.FindSet() then
+            repeat
+                Customer.CalcFields("Balance (LCY)");
+                if Customer."Balance (LCY)" > Customer."Credit Limit (LCY)" then
+                    CustomerNos.Add(Customer."No.");
+            until Customer.Next() = 0;
+    end;
+}

microsoft/knowledge/performance/use-setautocalcfields-for-per-row-flowfields.good.al

@@ -0,0 +1,16 @@
+codeunit 50490 "Perf AutoCalcFields Good"
+{
+    procedure CollectOverLimitCustomers(var CustomerNos: List of [Code[20]])
+    var
+        Customer: Record Customer;
+    begin
+        Customer.SetLoadFields("Credit Limit (LCY)");
+        Customer.SetFilter("Credit Limit (LCY)", '>0');
+        Customer.SetAutoCalcFields("Balance (LCY)");
+        if Customer.FindSet() then
+            repeat
+                if Customer."Balance (LCY)" > Customer."Credit Limit (LCY)" then
+                    CustomerNos.Add(Customer."No.");
+            until Customer.Next() = 0;
+    end;
+}

microsoft/knowledge/performance/use-setautocalcfields-for-per-row-flowfields.md

@@ -0,0 +1,26 @@
+---
+bc-version: [all]
+domain: performance
+keywords: [setautocalcfields, calcfields, calcsums, flowfield, loop, per-row]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Use SetAutoCalcFields when each iterated row needs a FlowField
+
+## Description
+
+`Record.SetAutoCalcFields` has been available since runtime 1.0 and makes the specified FlowFields calculate as records are retrieved. Microsoft's [AL database-method performance guidance](https://learn.microsoft.com/en-us/dynamics365/business-central/dev-itpro/administration/optimize-sql-al-database-methods-and-performance-on-server#setautocalcfields) uses it to remove an explicit `CalcFields` call from every iteration when each row's FlowField drives a branch. This is different from `CalcSums`, which returns a total for the filtered set rather than a value for each row.
+
+## Best Practice
+
+Call `SetAutoCalcFields` before `FindSet` when every returned row needs the same FlowField for a comparison, branch, or per-record action. Use `CalcSums` instead when the required result is one aggregate over the filtered set (see `calcsums-instead-of-calcfields-in-loop.md`).
+
+See sample: `use-setautocalcfields-for-per-row-flowfields.good.al`.
+
+## Anti Pattern
+
+Calling `CalcFields` inside the loop when every iteration reads the same FlowField. Each `CalcFields` request requires a separate SQL statement unless a compatible recent result is cached. Do not replace row-specific decisions with `CalcSums`; an aggregate cannot preserve which rows met the condition.
+
+See sample: `use-setautocalcfields-for-per-row-flowfields.bad.al`.

microsoft/skills/review/al-performance-review.md

@@ -38,11 +38,16 @@ Discard files that are not applicable. Retain conditionally applicable files (an
 Narrow the relevant files to the subset that applies to the changes under review. For each relevant file, compute overlap against:
 
 - The changed AL object names and types — especially tables, pages with SourceTable bindings, reports, queries, and codeunits performing record iteration.
-- The changed procedures and triggers, weighted toward those that perform loops, Find/FindSet/FindFirst calls, CalcFields, CalcSums, FlowField access, or cross-table navigation.
-- Tokens extracted from the diff that relate to data access and hot-path costs (`SetRange`, `SetFilter`, `SetLoadFields`, `SetCurrentKey`, `FindSet`, `ReadIsolation`, `LockTable`, `ModifyAll`, `DeleteAll`, `TextBuilder`, `Dictionary`, `temporary`, `repeat`, `until`, `CalcFields`, `CalcSums`).
+- The changed procedures and triggers, weighted toward those that perform loops, Find/FindSet/FindFirst calls, CalcFields, SetAutoCalcFields, CalcSums, FlowField access, record copying, RecordRef conversion, Modify/Delete calls, or cross-table navigation.
+- Tokens extracted from the diff that relate to data access and hot-path costs (`SetRange`, `SetFilter`, `SetLoadFields`, `SetCurrentKey`, `FindSet`, `ReadIsolation`, `LockTable`, `ModifyAll`, `DeleteAll`, `Modify`, `Delete`, `Copy`, `RecordRef`, `GetTable`, `TextBuilder`, `Dictionary`, `temporary`, `repeat`, `until`, `CalcFields`, `SetAutoCalcFields`, `CalcSums`).
 
 A file enters the candidate worklist when its `keywords` intersect the extracted tokens or its topic (derived from the index entry's `path`, `title`, and `description`) matches a changed object type. Read an article's full file — its `## Best Practice` / `## Anti Pattern` bodies — only after it makes the worklist; candidate selection uses the index alone.
 
+Apply these targeted cues even when simple token overlap would rank the article below the worklist cutoff:
+
+- Worklist `use-setautocalcfields-for-per-row-flowfields.md` when a record loop calls `CalcFields`, or when every row reads the same FlowField for a comparison, branch, or per-record action. Worklist `calcsums-instead-of-calcfields-in-loop.md` instead when the loop only accumulates one set total.
+- Worklist `avoid-cloning-records-before-modify-delete-in-loops.md` when an iteration calls `Copy` or `RecordRef.GetTable` before `Modify`/`Delete`, or passes the iterated record without `var` to a helper that writes that record. Do not match a read-only copy, a temporary record, a different target table, or a `RecordRef` opened and iterated directly.
+
 Once the candidate worklist is known, resolve layer-precedence conflicts per READ. Drop lower-precedence files whose normative guidance (`## Best Practice` or `## Anti Pattern`) directly contradicts a higher-precedence candidate, and record each dropped file in `suppressed` with `reason: "layer-precedence"`. Files that would have been candidates but are hidden because their layer is disabled in consumer configuration are recorded with `reason: "configuration"`. Files that never became candidates are NOT recorded in `suppressed`.
 
 When the post-conflict worklist is empty because no applicable performance knowledge exists, or because configuration suppressed every candidate, emit `outcome: "no-knowledge"`. When the worklist is empty because no applicable performance knowledge matched the changes, emit `outcome: "completed"` with an empty `findings` array.