knowledge(performance): add community rules for performance (#134)

* knowledge(performance): add community rules for JIT, locks, and false positives

These articles capture BC-specific mechanics agents still invert: partial-record JIT on writes, Reset clearing SetLoadFields, HttpClient inside write transactions, and batched number series, plus negative guidance that stops over-eager Query and IsEmpty "fixes".

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(community/performance): address PR #134 review comments

Fixes technical inaccuracies and behavioral issues raised during review
of the community performance knowledge articles.

avoid-currpage-update-in-onaftergetrecord.md
- Removed OnAfterGetCurrRecord from the Best Practice section. That
  trigger is itself implicitly re-entered on every refresh, so placing
  CurrPage.Update(false) inside it can re-trigger the very loop the rule
  warns about. Only OnAction remains as the recommended location.

batch-number-series-instead-of-getnextno-per-row.md
- Scoped the lock/contention claim to gapless (Normal) series only.
  Added explicit statement that Allow Gaps series use NumberSequence
  sequences and do not hold the series-line lock, so the anti-pattern
  detection signal now excludes Allow Gaps series.

countapprox-for-progress-not-count.bad.al / .good.al
- Changed FindSet(true) to FindSet() in both samples. The loop is
  read-only; UpdLock is not needed and was misleading.

countapprox-for-progress-not-count.md
- Qualified the Count() cost claim: it is expensive only when no SIFT
  key covers all filtered fields (forcing a SELECT COUNT(*)); a filtered
  count with matching SIFT coverage is cheap. Added a parenthetical
  noting that SIFT coverage cannot be assumed for arbitrary filters.

dataaccessintent-readonly-on-analytical-objects.md
- Changed bc-version from [all] to ["16.."]. DataAccessIntent was
  introduced at runtime 5.0 / BC 16 and has no effect in earlier
  versions.
- Added precision to the supported objects: pages must be PageType=API
  with Editable=false; for queries, replica routing only applies when
  the query is exposed via OData/API, not for AL-to-AL calls.

httpclient-inside-write-transaction-holds-locks.good.al
- Replaced the Commit()-before-HttpClient pattern with a two-codeunit
  task-deferral pattern. The write completes inside the caller's
  transaction (locks released naturally when it ends); a TaskScheduler
  task runs the HTTP call in a separate session where no write-
  transaction lock is held.

httpclient-inside-write-transaction-holds-locks.md
- Changed Best Practice to recommend TaskScheduler/job queue deferral
  as the primary remedy.
- Added an explicit warning against Commit() as a generic remedy: it
  irrevocably commits all prior writes in the current transaction, so a
  subsequent failure cannot roll them back. Commit() is appropriate only
  at top-level entry points where partial persistence is intentional.

oncompanyopen-subscribers-must-not-do-io.good.al
- Added a ClientType guard so the subscriber exits immediately in
  background task sessions (OnAfterLogin fires there too, which would
  create an unbounded task chain without the guard).
- Added a TaskScheduler.TaskExists idempotency check to avoid queuing
  duplicate tasks on repeated logins.
- Fixed the error-fallback codeunit in CreateTask from a self-reference
  to 0 (no error codeunit).
- Added a 60-second delay (CurrentDateTime() + 60000) so the task does
  not compete with the login session itself.

prefer-related-table-over-extension-on-hot-ledgers.md
- Changed bc-version from [all] to ["23.."]. The companion-table join
  optimisation (single join per base table, automatic exclusion on List/
  OData pages with partial records) was introduced in v23.
- Scoped the "join is always paid" claim: since v23 the join is
  excluded on List/ListPart/OData pages when no extension field is
  loaded under partial-record semantics, but it is still paid on every
  posting path and any AL code that accesses an extension field.

skip-setloadfields-on-write-and-transferfields.bad.al / .good.al / .md
- Changed the example scenario from Modify(false) (which is actually
  valid with a partial record) to TransferFields+Insert into a temporary
  record, which is a documented full-load operation.
- Removed Modify from the list of operations that force a full load.
- Added an explicit note in the .md that Modify itself is not in the
  full-load list; SetLoadFields is safe to use before Modify(false).

use-dedicated-lookup-pages-not-full-lists.bad.al
- Added a separate CardPart page definition (50101) to replace the
  self-referencing FactBox part that referenced the same list page it
  was embedded in. A part cannot refer to its own container page.

validate-on-partial-record-forces-jit.good.al
- Restored SetLoadFields to the good sample so it exercises a partial
  record and the contrast with .bad.al is field selection, not the
  absence of the feature. The good sample loads both Name and Search
  Name (the field Name.OnValidate writes), while the bad sample loads
  only Name, causing a JIT reload of Search Name on every Validate call.

* fix(community/performance): correct httpclient and oncompanyopen good samples

httpclient-inside-write-transaction-holds-locks.good.al
- Pass Customer.RecordId as the last argument to CreateTask so the task
  is bound to the single customer that was written, not to all customers.
- Declare TableNo = Customer on the task codeunit so the platform loads
  the bound record into Rec automatically when OnRun executes.
- Replace the FindSet loop over all customers with Rec."No.", preserving
  the one-customer scope of the original SyncCustomerLastName procedure.

oncompanyopen-subscribers-must-not-do-io.good.al
- Replace Session.GetCurrentClientType() with Session.CurrentClientType(),
  the correct platform method name.
- Fix the idempotency check: TaskScheduler.TaskExists() requires a Guid,
  not a codeunit integer ID. Store the Guid returned by CreateTask in
  IsolatedStorage (DataScope::Company) under a fixed key; on the next
  login read it back as Text, Evaluate it to Guid, and pass that Guid to
  TaskExists so the type matches the method signature.

* fix(community/performance): address review feedback

---------

Co-authored-by: Cursor <cursoragent@cursor.com>

community/knowledge/performance/avoid-currpage-update-in-onaftergetrecord.bad.al

@@ -0,0 +1,24 @@
+page 50100 "CurrPage Update OAGR Bad"
+{
+    PageType = List;
+    SourceTable = Customer;
+    ApplicationArea = All;
+
+    layout
+    {
+        area(content)
+        {
+            repeater(Rows)
+            {
+                field("No."; Rec."No.") { }
+                field(Name; Rec.Name) { }
+            }
+        }
+    }
+
+    trigger OnAfterGetRecord()
+    begin
+        // Update from OnAfterGetRecord re-enters the trigger on every row.
+        CurrPage.Update(false);
+    end;
+}

community/knowledge/performance/avoid-currpage-update-in-onaftergetrecord.good.al

@@ -0,0 +1,26 @@
+page 50100 "CurrPage Update OAGR Good"
+{
+    PageType = List;
+    SourceTable = Customer;
+    ApplicationArea = All;
+
+    layout
+    {
+        area(content)
+        {
+            repeater(Rows)
+            {
+                field("No."; Rec."No.") { }
+                field(Warning; WarningText) { }
+            }
+        }
+    }
+
+    var
+        WarningText: Text[50];
+
+    trigger OnAfterGetRecord()
+    begin
+        WarningText := CopyStr(Rec.Name, 1, MaxStrLen(WarningText));
+    end;
+}

community/knowledge/performance/avoid-currpage-update-in-onaftergetrecord.md

@@ -0,0 +1,28 @@
+---
+bc-version: [all]
+domain: performance
+keywords: [currpage-update, onaftergetrecord, list-page, scroll, refresh]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Do not call CurrPage.Update inside OnAfterGetRecord
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+`OnAfterGetRecord` on a list already runs once per visible row on scroll and refresh. `CurrPage.Update` asks the page to reload, which fires those triggers again. The result is a refresh loop or a stutter on every row paint. Official developer performance guidance lists `CurrPage.Update()` in `OnAfterGetRecord` next to `Modify` as work that must not live there. Sibling of `do-not-modify-in-onaftergetrecord.md` (writes); this file is the client refresh half.
+
+## Best Practice
+
+Put display-only results in page variables assigned in `OnAfterGetRecord` without calling `Update`. If the page must refresh after an action, call `CurrPage.Update(false)` from `OnAction` once, not per row.
+
+See sample: `avoid-currpage-update-in-onaftergetrecord.good.al`.
+
+## Anti Pattern
+
+`trigger OnAfterGetRecord() begin ... CurrPage.Update(); end;` on a list. The signal is `CurrPage.Update` inside `OnAfterGetRecord` or `OnAfterGetCurrRecord` without an explicit user action.
+
+See sample: `avoid-currpage-update-in-onaftergetrecord.bad.al`.

community/knowledge/performance/batch-number-series-instead-of-getnextno-per-row.bad.al

@@ -0,0 +1,20 @@
+codeunit 50100 "Batch NoSeries Insert Bad"
+{
+    procedure InsertDraftOrders(var Customer: Record Customer)
+    var
+        SalesHeader: Record "Sales Header";
+        SalesSetup: Record "Sales & Receivables Setup";
+        NoSeries: Codeunit "No. Series";
+    begin
+        SalesSetup.Get();
+        if Customer.FindSet() then
+            repeat
+                SalesHeader.Init();
+                SalesHeader."Document Type" := SalesHeader."Document Type"::Order;
+                // Per-row GetNextNo locks the number-series line every insert.
+                SalesHeader."No." := NoSeries.GetNextNo(SalesSetup."Order Nos.", WorkDate());
+                SalesHeader."Sell-to Customer No." := Customer."No.";
+                SalesHeader.Insert(true);
+            until Customer.Next() = 0;
+    end;
+}

community/knowledge/performance/batch-number-series-instead-of-getnextno-per-row.good.al

@@ -0,0 +1,20 @@
+codeunit 50100 "Batch NoSeries Insert Good"
+{
+    procedure InsertDraftOrders(var Customer: Record Customer)
+    var
+        SalesHeader: Record "Sales Header";
+        SalesSetup: Record "Sales & Receivables Setup";
+        NoSeriesBatch: Codeunit "No. Series - Batch";
+    begin
+        SalesSetup.Get();
+        if Customer.FindSet() then
+            repeat
+                SalesHeader.Init();
+                SalesHeader."Document Type" := SalesHeader."Document Type"::Order;
+                SalesHeader."No." := NoSeriesBatch.GetNextNo(SalesSetup."Order Nos.", WorkDate());
+                SalesHeader."Sell-to Customer No." := Customer."No.";
+                SalesHeader.Insert(true);
+            until Customer.Next() = 0;
+        NoSeriesBatch.SaveState();
+    end;
+}

community/knowledge/performance/batch-number-series-instead-of-getnextno-per-row.md

@@ -0,0 +1,28 @@
+---
+bc-version: [22..]
+domain: performance
+keywords: [no-series, getnextno, no-series-batch, savestate, numbersequence, lock]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Batch number-series calls instead of GetNextNo per insert
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+`Codeunit "No. Series".GetNextNo` on a **gapless (Normal)** series updates and locks the number-series line on every call. A tight `Insert` loop that asks for a number per row serializes every concurrent writer on that series — the classic SaaS posting bottleneck. Training data still copies the per-row C/AL `NoSeriesManagement` shape. Series configured with **Allow Gaps** instead obtain numbers through `NumberSequence` and do not hold the series-line lock between calls, so they are not affected by this pattern. Codeunit `"No. Series - Batch"` issues gapless numbers in memory and writes the series line once via `SaveState`.
+
+## Best Practice
+
+Inside a multi-row insert, call `"No. Series - Batch".GetNextNo` per row and `SaveState` once after the loop when the series must remain gapless. Use `NumberSequence.Next` when holes are allowed. Do not replace a single `OnInsert` `GetNextNo` for one master record; that path is not the hotspot.
+
+See sample: `batch-number-series-instead-of-getnextno-per-row.good.al`.
+
+## Anti Pattern
+
+`NoSeries.GetNextNo(...)` inside `repeat ... Insert ... until Next() = 0` where the series is **gapless** (Allow Gaps = false). Each iteration takes the series-line lock. The signal is `"No. Series"` (not `"No. Series - Batch"`) in a loop that inserts more than one row; do not flag the same pattern when the series has Allow Gaps enabled, as the `NumberSequence` path already avoids the lock.
+
+See sample: `batch-number-series-instead-of-getnextno-per-row.bad.al`.

community/knowledge/performance/changecompany-in-loop-drops-caches.bad.al

@@ -0,0 +1,20 @@
+codeunit 50100 "ChangeCompany Loop Bad"
+{
+    procedure NamesForCustomers(var Buffer: Record Customer)
+    var
+        Customer: Record Customer;
+        Company: Record Company;
+    begin
+        Customer.SetLoadFields(Name);
+        if Buffer.FindSet() then
+            repeat
+                if Company.FindSet() then
+                    repeat
+                        // ChangeCompany per customer per company resets caches every row.
+                        Customer.ChangeCompany(Company.Name);
+                        if Customer.Get(Buffer."No.") then
+                            Message(Customer.Name);
+                    until Company.Next() = 0;
+            until Buffer.Next() = 0;
+    end;
+}

community/knowledge/performance/changecompany-in-loop-drops-caches.good.al

@@ -0,0 +1,19 @@
+codeunit 50100 "ChangeCompany Loop Good"
+{
+    procedure NamesForCustomers(var Buffer: Record Customer)
+    var
+        Customer: Record Customer;
+        Company: Record Company;
+    begin
+        Customer.SetLoadFields(Name);
+        if Company.FindSet() then
+            repeat
+                Customer.ChangeCompany(Company.Name);
+                if Buffer.FindSet() then
+                    repeat
+                        if Customer.Get(Buffer."No.") then
+                            Message(Customer.Name);
+                    until Buffer.Next() = 0;
+            until Company.Next() = 0;
+    end;
+}

community/knowledge/performance/changecompany-in-loop-drops-caches.md

@@ -0,0 +1,28 @@
+---
+bc-version: [all]
+domain: performance
+keywords: [changecompany, loop, cache, multi-company, isolation]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Do not call ChangeCompany inside a per-row loop
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+`ChangeCompany` retargets a record variable to another company's data and drops the in-memory caches bound to the previous company. Calling it once per row in a multi-company scan therefore pays a cache reset on every iteration, even when consecutive rows share a company. Agents treat `ChangeCompany` like a filter. It is an isolation switch.
+
+## Best Practice
+
+Group work by company. Call `ChangeCompany` once per distinct company, then `FindSet`/`Get` that company's rows. If the record variable is reused afterward, call `ChangeCompany()` without a company name to redirect it back to the current company.
+
+See sample: `changecompany-in-loop-drops-caches.good.al`.
+
+## Anti Pattern
+
+`repeat Rec.ChangeCompany(Buffer.Company); Rec.Get(Buffer."No."); until Buffer.Next() = 0` when `Buffer` is not ordered by company, or even when it is — if `ChangeCompany` still runs every row. The signal is `ChangeCompany` inside `repeat`/`while` keyed by a document line rather than by a company loop.
+
+See sample: `changecompany-in-loop-drops-caches.bad.al`.

community/knowledge/performance/dataaccessintent-readonly-on-analytical-objects.bad.al

@@ -0,0 +1,15 @@
+report 50100 "Cust List ReadOnly Bad"
+{
+    UsageCategory = ReportsAndAnalysis;
+    ApplicationArea = All;
+    // Missing DataAccessIntent = ReadOnly; the scan hits the primary replica.
+
+    dataset
+    {
+        dataitem(Customer; Customer)
+        {
+            column(No; "No.") { }
+            column(Name; Name) { }
+        }
+    }
+}

community/knowledge/performance/dataaccessintent-readonly-on-analytical-objects.good.al

@@ -0,0 +1,15 @@
+report 50100 "Cust List ReadOnly Good"
+{
+    UsageCategory = ReportsAndAnalysis;
+    ApplicationArea = All;
+    DataAccessIntent = ReadOnly;
+
+    dataset
+    {
+        dataitem(Customer; Customer)
+        {
+            column(No; "No.") { }
+            column(Name; Name) { }
+        }
+    }
+}

community/knowledge/performance/dataaccessintent-readonly-on-analytical-objects.md

@@ -0,0 +1,28 @@
+---
+bc-version: ["16.."]
+domain: performance
+keywords: [dataaccessintent, read-only, read-scale-out, report, api-page, query]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Set DataAccessIntent ReadOnly on analytical objects
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+`DataAccessIntent` was introduced at runtime 5.0 (BC 16) and has no effect in earlier versions. Reports, API pages (`PageType = API` with `Editable = false`), and queries that only read can run against a read replica when `DataAccessIntent = ReadOnly`. For queries, replica routing only applies when the query is exposed via OData/API; running a query in AL code is unaffected. Without the property these objects hit the primary replica and compete with posting. Agents omit it because the default is read-write and the object "only reads" in AL. The replica routing is a metadata switch, not something the compiler infers from the absence of `Modify`.
+
+## Best Practice
+
+On report objects and `PageType = API` pages with `Editable = false` that never write, set `DataAccessIntent = ReadOnly`. For query objects, set it when the query is consumed via OData or an API endpoint. Keep the default on objects that insert, modify, or call a write codeunit from a processing-only report.
+
+See sample: `dataaccessintent-readonly-on-analytical-objects.good.al`.
+
+## Anti Pattern
+
+A listing report or API query with no `DataAccessIntent` that scans G/L or sales lines. The object is read-only in practice and still loads the primary.
+
+See sample: `dataaccessintent-readonly-on-analytical-objects.bad.al`.

community/knowledge/performance/guiallowed-guard-on-pages-used-as-odata.bad.al

@@ -0,0 +1,34 @@
+page 50100 "GuiAllowed OData Guard Bad"
+{
+    PageType = List;
+    SourceTable = Customer;
+    ApplicationArea = All;
+
+    layout
+    {
+        area(content)
+        {
+            repeater(Rows)
+            {
+                field("No."; Rec."No.") { }
+                field(Name; Rec.Name)
+                {
+                    StyleExpr = NameStyle;
+                }
+            }
+        }
+    }
+
+    var
+        NameStyle: Text;
+
+    trigger OnAfterGetRecord()
+    begin
+        // UI-only styling still runs for every OData / Edit-in-Excel row.
+        Rec.CalcFields("Balance (LCY)");
+        if Rec."Balance (LCY)" > 0 then
+            NameStyle := 'Attention'
+        else
+            NameStyle := 'Standard';
+    end;
+}

community/knowledge/performance/guiallowed-guard-on-pages-used-as-odata.good.al

@@ -0,0 +1,35 @@
+page 50100 "GuiAllowed OData Guard Good"
+{
+    PageType = List;
+    SourceTable = Customer;
+    ApplicationArea = All;
+
+    layout
+    {
+        area(content)
+        {
+            repeater(Rows)
+            {
+                field("No."; Rec."No.") { }
+                field(Name; Rec.Name)
+                {
+                    StyleExpr = NameStyle;
+                }
+            }
+        }
+    }
+
+    var
+        NameStyle: Text;
+
+    trigger OnAfterGetRecord()
+    begin
+        if not GuiAllowed then
+            exit;
+        Rec.CalcFields("Balance (LCY)");
+        if Rec."Balance (LCY)" > 0 then
+            NameStyle := 'Attention'
+        else
+            NameStyle := 'Standard';
+    end;
+}

community/knowledge/performance/guiallowed-guard-on-pages-used-as-odata.md

@@ -0,0 +1,28 @@
+---
+bc-version: [all]
+domain: performance
+keywords: [guiallowed, clienttype, odata, edit-in-excel, page-trigger, factbox]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Guard page trigger work with GuiAllowed for OData and Excel
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+Pages exposed as OData, including Edit in Excel, still run AL page triggers for every row returned. FactBox updates, defaulting, and extra `CalcFields` in `OnAfterGetRecord` therefore run on the web-service path where no UI exists. `GuiAllowed` is false for those sessions. Agents add page logic as if only the browser client will execute it.
+
+## Best Practice
+
+Wrap UI-only work — FactBox refresh, notifications, defaulting that is not part of the web-service contract — in `if GuiAllowed then`. Keep the OData path to field values the API actually returns.
+
+See sample: `guiallowed-guard-on-pages-used-as-odata.good.al`.
+
+## Anti Pattern
+
+Unconditional FactBox or calculation logic in `OnAfterGetRecord` / `OnAfterGetCurrRecord` on a page that is published as a web service or used with Edit in Excel. The signal is trigger work that calls `CurrPage` parts or extra queries without a `GuiAllowed` guard.
+
+See sample: `guiallowed-guard-on-pages-used-as-odata.bad.al`.

community/knowledge/performance/httpclient-inside-write-transaction-holds-locks.bad.al

@@ -0,0 +1,13 @@
+codeunit 50100 "HttpClient Holds Locks Bad"
+{
+    procedure SyncCustomerLastName(var Customer: Record Customer)
+    var
+        Client: HttpClient;
+        Response: HttpResponseMessage;
+    begin
+        Customer."Search Name" := Customer.Name;
+        Customer.Modify(false);
+        // Locks from Modify are held for the entire HTTP wait.
+        Client.Get(StrSubstNo('https://example.local/sync/%1', Customer."No."), Response);
+    end;
+}

community/knowledge/performance/httpclient-inside-write-transaction-holds-locks.good.al

@@ -0,0 +1,62 @@
+codeunit 50100 "HttpClient Holds Locks Good"
+{
+    procedure SyncCustomerLastName(var Customer: Record Customer)
+    var
+        CustomerSyncOutbox: Record "Customer Sync Outbox";
+    begin
+        Customer."Search Name" := Customer.Name;
+        Customer.Modify(false);
+
+        // This work item commits or rolls back with the customer change.
+        CustomerSyncOutbox."Customer No." := Customer."No.";
+        CustomerSyncOutbox.Insert();
+    end;
+}
+
+table 50100 "Customer Sync Outbox"
+{
+    DataClassification = CustomerContent;
+
+    fields
+    {
+        field(1; "Entry No."; Integer)
+        {
+            AutoIncrement = true;
+        }
+        field(2; "Customer No."; Code[20]) { }
+    }
+
+    keys
+    {
+        key(PK; "Entry No.")
+        {
+            Clustered = true;
+        }
+    }
+}
+
+codeunit 50101 "Customer Sync Outbox Worker"
+{
+    // Configure this codeunit as a recurring job queue entry.
+    TableNo = "Job Queue Entry";
+
+    trigger OnRun()
+    var
+        Customer: Record Customer;
+        CustomerSyncOutbox: Record "Customer Sync Outbox";
+        Client: HttpClient;
+        Response: HttpResponseMessage;
+    begin
+        // Only committed work is visible here; a rolled-back change leaves no outbox row.
+        if not CustomerSyncOutbox.FindFirst() then
+            exit;
+
+        Customer.Get(CustomerSyncOutbox."Customer No.");
+        Client.Get(StrSubstNo('https://example.local/sync/%1', Customer."No."), Response);
+        if not Response.IsSuccessStatusCode() then
+            Error('Customer sync failed with HTTP status %1.', Response.HttpStatusCode());
+
+        // Delete only after HTTP completes, so no write lock is held during the call.
+        CustomerSyncOutbox.Delete();
+    end;
+}

community/knowledge/performance/httpclient-inside-write-transaction-holds-locks.md

@@ -0,0 +1,30 @@
+---
+bc-version: [all]
+domain: performance
+keywords: [httpclient, write-transaction, lock, commit, outbound-http, session-block]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Do not call HttpClient inside an open write transaction
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+The first database write opens an AL write transaction that the runtime holds until the execution completes or `Commit()` runs — see `understand-implicit-transaction-boundary.md`. `HttpClient` blocks the session until the remote call returns. Any locks taken by earlier `Insert`/`Modify`/`Delete` therefore stay held for the HTTP wall-clock time, and interactive users see a spinner. This is not generic "don't block": it is the AL transaction model plus lock lifetime around outbound I/O.
+
+## Best Practice
+
+Defer the HTTP call to a separate session. When the external operation must correspond to a committed database change, insert an outbox work item in the same transaction as that change and process committed outbox rows with a recurring job queue entry. The change and work item then commit or roll back together, and the worker performs HTTP before deleting the item so it holds no write lock during the call. Make the external operation idempotent because a failure after a successful HTTP response can cause the work item to be retried.
+
+A directly created scheduled task is suitable only when its work is independent of the caller's commit. An immediately ready task can run concurrently with the caller, so it must not assume that the caller's writes are already committed. Do **not** use `Commit()` as a general remedy: it irrevocably commits all prior writes in the current transaction, so any subsequent failure cannot roll them back. `Commit()` is appropriate only at top-level entry points where partial persistence is intentional and understood.
+
+See sample: `httpclient-inside-write-transaction-holds-locks.good.al`.
+
+## Anti Pattern
+
+`Modify`/`Insert` followed by `HttpClient` in the same procedure with no `Commit` between them. Detection signal: any `HttpClient` use after a write on the same execution path, especially in posting, page actions, or subscribers.
+
+See sample: `httpclient-inside-write-transaction-holds-locks.bad.al`.

community/knowledge/performance/isempty-before-findset-is-extra-round-trip.bad.al

@@ -0,0 +1,16 @@
+codeunit 50100 "IsEmpty Before FindSet Bad"
+{
+    procedure ListUsCustomerNames()
+    var
+        Customer: Record Customer;
+    begin
+        Customer.SetLoadFields(Name);
+        Customer.SetRange("Country/Region Code", 'US');
+        // IsEmpty does not replace FindSet; it adds a second round-trip.
+        if not Customer.IsEmpty() then
+            if Customer.FindSet() then
+                repeat
+                    Message(Customer.Name);
+                until Customer.Next() = 0;
+    end;
+}

community/knowledge/performance/isempty-before-findset-is-extra-round-trip.good.al

@@ -0,0 +1,14 @@
+codeunit 50100 "IsEmpty Before FindSet Good"
+{
+    procedure ListUsCustomerNames()
+    var
+        Customer: Record Customer;
+    begin
+        Customer.SetLoadFields(Name);
+        Customer.SetRange("Country/Region Code", 'US');
+        if Customer.FindSet() then
+            repeat
+                Message(Customer.Name);
+            until Customer.Next() = 0;
+    end;
+}

community/knowledge/performance/isempty-before-findset-is-extra-round-trip.md

@@ -0,0 +1,28 @@
+---
+bc-version: [all]
+domain: performance
+keywords: [isempty, findset, extra-round-trip, existence-check, false-positive]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# IsEmpty immediately before FindSet is an extra round-trip
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+`IsEmpty` is the right API when the caller only needs existence — see `microsoft/knowledge/performance/use-isempty-for-existence-check.md`. It is not a cheap guard in front of a loop that will `FindSet` anyway. Both calls hit the database; `FindSet` already returns false when the filter matches nothing. Agents and reviewers often insert `if not Rec.IsEmpty() then` "for performance" and pay a second query for a result the iterator already provides.
+
+## Best Practice
+
+When the body iterates, open with `if Rec.FindSet() then repeat ... until Next() = 0`. Do not flag a bare `FindSet` loop as missing an `IsEmpty` precondition. Reserve `IsEmpty` for branches that never materialize the row set.
+
+See sample: `isempty-before-findset-is-extra-round-trip.good.al`.
+
+## Anti Pattern
+
+`if not Rec.IsEmpty() then if Rec.FindSet() then repeat`. Also a false-positive review comment that asks to add that guard. The second read does not avoid the first; it duplicates it.
+
+See sample: `isempty-before-findset-is-extra-round-trip.bad.al`.

community/knowledge/performance/oncompanyopen-subscribers-must-not-do-io.bad.al

@@ -0,0 +1,15 @@
+codeunit 50100 "Login Subscriber IO Bad"
+{
+    [EventSubscriber(ObjectType::Codeunit, Codeunit::"System Initialization", OnAfterLogin, '', false, false)]
+    local procedure OnAfterLogin()
+    var
+        Client: HttpClient;
+        Response: HttpResponseMessage;
+        GLEntry: Record "G/L Entry";
+    begin
+        // Blocks UI, API, and job-queue session creation until HTTP and SQL finish.
+        Client.Get('https://example.local/warmup', Response);
+        GLEntry.SetLoadFields("Entry No.");
+        if GLEntry.FindLast() then;
+    end;
+}

community/knowledge/performance/oncompanyopen-subscribers-must-not-do-io.good.al

@@ -0,0 +1,30 @@
+codeunit 50100 "Login Subscriber IO Good"
+{
+    [EventSubscriber(ObjectType::Codeunit, Codeunit::"System Initialization", OnAfterLogin, '', false, false)]
+    local procedure OnAfterLogin()
+    var
+        TaskId: Guid;
+        StoredId: Text;
+    begin
+        // Guard to interactive sessions only; background task sessions also raise OnAfterLogin.
+        if not (Session.CurrentClientType() in [ClientType::Web, ClientType::Windows, ClientType::Desktop, ClientType::Tablet, ClientType::Phone]) then
+            exit;
+
+        // Idempotent: TaskExists requires the GUID returned by CreateTask, stored across logins.
+        if IsolatedStorage.Get('LoginSyncTaskId', DataScope::Company, StoredId) then
+            if Evaluate(TaskId, StoredId) then
+                if TaskScheduler.TaskExists(TaskId) then
+                    exit;
+
+        TaskId := TaskScheduler.CreateTask(Codeunit::"Login Subscriber IO Work", 0, true, CompanyName(), CurrentDateTime() + 60000);
+        IsolatedStorage.Set('LoginSyncTaskId', Format(TaskId), DataScope::Company);
+    end;
+}
+
+codeunit 50101 "Login Subscriber IO Work"
+{
+    trigger OnRun()
+    begin
+        // Isolated from session creation: outbound I/O is safe here.
+    end;
+}

community/knowledge/performance/oncompanyopen-subscribers-must-not-do-io.md

@@ -0,0 +1,28 @@
+---
+bc-version: [all]
+domain: performance
+keywords: [oncompanyopen, onafterlogin, session-start, httpclient, subscriber, login]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Session-open subscribers must not do I/O
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+`OnCompanyOpen`, `OnCompanyOpenCompleted`, and `System Initialization`.OnAfterLogin run while the session is being created. The platform waits until every subscriber returns before the UI, an API call, or a background session can proceed. `HttpClient` or a heavy `FindSet` here delays **every** session type, not just the user who "opened the company". Agents still put warmup sync, license checks, and HTTP probes on these events because they look like an application startup hook.
+
+## Best Practice
+
+Keep company-open subscribers to cheap in-memory work: set a flag, enqueue a job-queue entry, or `TaskScheduler.CreateTask`. Perform HTTP and large SQL after the session is running, in that background work.
+
+See sample: `oncompanyopen-subscribers-must-not-do-io.good.al`.
+
+## Anti Pattern
+
+An `OnAfterLogin` / `OnCompanyOpenCompleted` subscriber that calls `HttpClient` or scans a ledger. Detection signal: `HttpClient`, `FindSet`, or `CalcFields` inside a subscriber bound to those events.
+
+See sample: `oncompanyopen-subscribers-must-not-do-io.bad.al`.

community/knowledge/performance/page-background-tasks-for-expensive-cues.bad.al

@@ -0,0 +1,31 @@
+page 50100 "Cue Background Task Bad"
+{
+    PageType = CardPart;
+    ApplicationArea = All;
+
+    layout
+    {
+        area(content)
+        {
+            cuegroup(Group)
+            {
+                field(OpenOrders; OpenOrderCount)
+                {
+                    Caption = 'Open Sales Orders';
+                }
+            }
+        }
+    }
+
+    var
+        OpenOrderCount: Integer;
+
+    trigger OnOpenPage()
+    var
+        SalesHeader: Record "Sales Header";
+    begin
+        // Blocks Role Center render on an exact count of sales headers.
+        SalesHeader.SetRange("Document Type", SalesHeader."Document Type"::Order);
+        OpenOrderCount := SalesHeader.Count();
+    end;
+}

community/knowledge/performance/page-background-tasks-for-expensive-cues.good.al

@@ -0,0 +1,49 @@
+page 50100 "Cue Background Task Good"
+{
+    PageType = CardPart;
+    ApplicationArea = All;
+
+    layout
+    {
+        area(content)
+        {
+            cuegroup(Group)
+            {
+                field(OpenOrders; OpenOrderCount)
+                {
+                    Caption = 'Open Sales Orders';
+                }
+            }
+        }
+    }
+
+    var
+        OpenOrderCount: Integer;
+        TaskId: Integer;
+
+    trigger OnAfterGetCurrRecord()
+    var
+        Args: Dictionary of [Text, Text];
+    begin
+        CurrPage.EnqueueBackgroundTask(TaskId, Codeunit::"Cue Open Order Count", Args);
+    end;
+
+    trigger OnPageBackgroundTaskCompleted(CompletedTaskId: Integer; Results: Dictionary of [Text, Text])
+    begin
+        if Results.ContainsKey('Count') then
+            Evaluate(OpenOrderCount, Results.Get('Count'));
+    end;
+}
+
+codeunit 50100 "Cue Open Order Count"
+{
+    trigger OnRun()
+    var
+        SalesHeader: Record "Sales Header";
+        Results: Dictionary of [Text, Text];
+    begin
+        SalesHeader.SetRange("Document Type", SalesHeader."Document Type"::Order);
+        Results.Add('Count', Format(SalesHeader.CountApprox()));
+        Page.SetBackgroundTaskResult(Results);
+    end;
+}

community/knowledge/performance/page-background-tasks-for-expensive-cues.md

@@ -0,0 +1,28 @@
+---
+bc-version: [15..]
+domain: performance
+keywords: [page-background-task, cue, rolecenter, enqueuebackgroundtask, ui-thread]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Calculate expensive cues on a page background task
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+Role-center cues and CardPart totals that run `CalcFields`, scans, or HTTP on the UI thread freeze the shell until they finish. Page background tasks exist to return the page immediately and fill the number later. Enqueue mechanics, cancellation, and the read-only child session are covered in `microsoft/knowledge/ui/page-background-tasks.md`. This file is the performance trigger: a cue whose value is not needed to *open* the page must not run on the render path.
+
+## Best Practice
+
+Bind the cue to a page variable, enqueue a read-only calculation from `OnAfterGetCurrRecord` (not `OnAfterGetRecord` on a list), and apply the result in `OnPageBackgroundTaskCompleted`. Show a placeholder until then.
+
+See sample: `page-background-tasks-for-expensive-cues.good.al`.
+
+## Anti Pattern
+
+`CalcFields` or a ledger `Count` in `OnOpenPage` / `OnAfterGetCurrRecord` of a CueGroup CardPart with no background task. The Role Center waits on SQL the user may never look at.
+
+See sample: `page-background-tasks-for-expensive-cues.bad.al`.

community/knowledge/performance/pass-var-record-to-preserve-partial-load-enumerator.bad.al

@@ -0,0 +1,20 @@
+codeunit 50100 "Pass Var Enumerator Bad"
+{
+    procedure ListUsCustomerCities()
+    var
+        Customer: Record Customer;
+    begin
+        Customer.SetLoadFields(Name);
+        Customer.SetRange("Country/Region Code", 'US');
+        if Customer.FindSet() then
+            repeat
+                // By-value copy: JIT on City does not update the enumerator.
+                Message(Customer.Name + ' ' + CityOf(Customer));
+            until Customer.Next() = 0;
+    end;
+
+    local procedure CityOf(Customer: Record Customer): Text
+    begin
+        exit(Customer.City);
+    end;
+}

community/knowledge/performance/pass-var-record-to-preserve-partial-load-enumerator.good.al

@@ -0,0 +1,21 @@
+codeunit 50100 "Pass Var Enumerator Good"
+{
+    procedure ListUsCustomerCities()
+    var
+        Customer: Record Customer;
+    begin
+        Customer.SetLoadFields(Name);
+        Customer.SetRange("Country/Region Code", 'US');
+        if Customer.FindSet() then
+            repeat
+                EnsureCityLoaded(Customer);
+                Message(Customer.Name + ' ' + Customer.City);
+            until Customer.Next() = 0;
+    end;
+
+    local procedure EnsureCityLoaded(var Customer: Record Customer)
+    begin
+        if not Customer.AreFieldsLoaded(Customer.City) then
+            Customer.LoadFields(Customer.City);
+    end;
+}

community/knowledge/performance/pass-var-record-to-preserve-partial-load-enumerator.md

@@ -0,0 +1,28 @@
+---
+bc-version: [all]
+domain: performance
+keywords: [setloadfields, jit-load, enumerator, var-parameter, pass-by-value, next]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Pass the iterated record var so a JIT load updates the enumerator
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+A `FindSet`/`Next` loop builds an enumerator from the fields selected for load. Accessing an unloaded field triggers a JIT load. When the record is passed **by value**, the copy does not share that enumerator: the JIT loads the copy and leaves the enumerator unchanged, so **every later `Next()` JIT-loads again**. Passing `var` lets the first JIT update the enumerator. `AddLoadFields` on the original record before a by-value call is the other fix. This is independent of whether `SetLoadFields` was ordered before filters.
+
+## Best Practice
+
+Helpers that read extra fields on an in-flight iterator must take the record as `var`, or the caller must `AddLoadFields` those fields before the loop. Prefer declaring the extra fields up front so no JIT is needed.
+
+See sample: `pass-var-record-to-preserve-partial-load-enumerator.good.al`.
+
+## Anti Pattern
+
+A `SetLoadFields` loop that passes the iterator by value into a helper which then reads a field that was not loaded. The first row pays one JIT; every subsequent row pays it again because the enumerator never learned the extra field.
+
+See sample: `pass-var-record-to-preserve-partial-load-enumerator.bad.al`.

community/knowledge/performance/prefer-related-table-over-extension-on-hot-ledgers.bad.al

@@ -0,0 +1,9 @@
+tableextension 50100 "G/L Entry Extra Ext" extends "G/L Entry"
+{
+    fields
+    {
+        // Stored companion columns are joined on every G/L Entry read.
+        field(50100; "External Reference"; Text[50]) { }
+        field(50101; "Integration Payload"; Blob) { }
+    }
+}

community/knowledge/performance/prefer-related-table-over-extension-on-hot-ledgers.good.al

@@ -0,0 +1,19 @@
+table 50100 "G/L Entry Extra"
+{
+    Caption = 'G/L Entry Extra';
+    DataClassification = CustomerContent;
+
+    fields
+    {
+        field(1; "Entry No."; Integer)
+        {
+            TableRelation = "G/L Entry"."Entry No.";
+        }
+        field(2; "External Reference"; Text[50]) { }
+    }
+
+    keys
+    {
+        key(PK; "Entry No.") { Clustered = true; }
+    }
+}

community/knowledge/performance/prefer-related-table-over-extension-on-hot-ledgers.md

@@ -0,0 +1,29 @@
+---
+bc-version: ["23.."]
+domain: performance
+keywords: [tableextension, companion-table, gl-entry, related-table, flowfield, hot-table]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Prefer a related table over stored fields on hot ledgers
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+Since v23, all extensions on the same base table share at most one companion-table join, and the platform automatically excludes that join on List, ListPart, and OData pages when partial records are in effect and no extension field is loaded. However, the join is still paid on every posting path and any AL code that accesses an extension field — or that runs without partial-record semantics. On hot tables — G/L Entry, Item Ledger Entry, Cust. Ledger Entry — even a single access per posted row adds up at volume. A related table keyed by the ledger `Entry No.`, optionally surfaced with a FlowField or FactBox, leaves the base read path entirely untouched. Agents extend G/L Entry because it is "where the posting already is".
+
+## Best Practice
+
+Put optional, sparse, or integration attributes in a related table with the ledger entry number as primary key. Show them from a FactBox or a FlowField. 
+Use a tableextension stored field only when the value must appear as a native list column and is read on almost every access.
+
+See sample: `prefer-related-table-over-extension-on-hot-ledgers.good.al`.
+
+## Anti Pattern
+
+`tableextension` on `"G/L Entry"` (or another posting table) that adds several stored `Text`/`Blob` fields used only by one integration. The companion join is paid on every posting and on any AL code path that loads extension fields, even when those columns are not needed for the current operation.
+
+See sample: `prefer-related-table-over-extension-on-hot-ledgers.bad.al`.

community/knowledge/performance/query-results-bypass-primary-key-cache.bad.al

@@ -0,0 +1,28 @@
+query 50100 "Query Bypass PK Cache Bad Q"
+{
+    QueryType = Normal;
+
+    elements
+    {
+        dataitem(Customer; Customer)
+        {
+            filter(NoFilter; "No.") { }
+            column(Name; Name) { }
+        }
+    }
+}
+
+codeunit 50100 "Query Bypass PK Cache Bad"
+{
+    procedure CustomerName(CustomerNo: Code[20]): Text
+    var
+        CustomerByNo: Query "Query Bypass PK Cache Bad Q";
+    begin
+        // Query Open/Read never hits the server PK cache.
+        CustomerByNo.SetRange(NoFilter, CustomerNo);
+        CustomerByNo.Open();
+        if CustomerByNo.Read() then
+            exit(CustomerByNo.Name);
+        CustomerByNo.Close();
+    end;
+}

community/knowledge/performance/query-results-bypass-primary-key-cache.good.al

@@ -0,0 +1,12 @@
+codeunit 50100 "Query Bypass PK Cache Good"
+{
+    procedure CustomerName(CustomerNo: Code[20]): Text
+    var
+        Customer: Record Customer;
+    begin
+        // Repeated Get of the same No. is served from the transaction PK cache.
+        Customer.SetLoadFields(Name);
+        if Customer.Get(CustomerNo) then
+            exit(Customer.Name);
+    end;
+}

community/knowledge/performance/query-results-bypass-primary-key-cache.md

@@ -0,0 +1,28 @@
+---
+bc-version: [all]
+domain: performance
+keywords: [query, primary-key-cache, get, false-positive, n-plus-one, record-cache]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Query results bypass the primary-key cache
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+The Business Central server caches primary-key `Get` calls within a transaction. Query objects do not use that cache: every `Open`/`Read` goes to SQL. `avoid-get-inside-loop-on-large-table.md` is right when an unbounded inner `Get`/`FindFirst` joins two large sets. It is wrong as a blanket rewrite of repeated `Get` on the same keys. Replacing a cached `Get` with a Query that re-executes per call can be slower. This file exists so reviewers stop treating every `Get` inside a loop as a Query candidate.
+
+## Best Practice
+
+Keep `Record.Get` for repeated lookups of the same primary keys in one transaction. Use a Query when the work is a true join or aggregation that the record API would express as nested scans. Do not flag a guarded `Get` on a repeating key as an N+1 solely because a Query could express the same columns.
+
+See sample: `query-results-bypass-primary-key-cache.good.al`.
+
+## Anti Pattern
+
+Rewriting a helper that `Get`s Customer by `No.` on every sales line into a Query opened inside that helper. Distinct line customers still need a lookup; repeating customers were already served from the PK cache. The Query pays SQL every time.
+
+See sample: `query-results-bypass-primary-key-cache.bad.al`.

community/knowledge/performance/reset-clears-partial-record-selection.bad.al

@@ -0,0 +1,16 @@
+codeunit 50100 "Reset Clears LoadFields Bad"
+{
+    procedure ListUsCustomerNames()
+    var
+        Customer: Record Customer;
+    begin
+        Customer.SetLoadFields(Name);
+        // Reset restores a full-row load; the SetLoadFields above is discarded.
+        Customer.Reset();
+        Customer.SetRange("Country/Region Code", 'US');
+        if Customer.FindSet() then
+            repeat
+                Message(Customer.Name);
+            until Customer.Next() = 0;
+    end;
+}

community/knowledge/performance/reset-clears-partial-record-selection.good.al

@@ -0,0 +1,15 @@
+codeunit 50100 "Reset Clears LoadFields Good"
+{
+    procedure ListUsCustomerNames()
+    var
+        Customer: Record Customer;
+    begin
+        Customer.Reset();
+        Customer.SetLoadFields(Name);
+        Customer.SetRange("Country/Region Code", 'US');
+        if Customer.FindSet() then
+            repeat
+                Message(Customer.Name);
+            until Customer.Next() = 0;
+    end;
+}

community/knowledge/performance/reset-clears-partial-record-selection.md

@@ -0,0 +1,28 @@
+---
+bc-version: [all]
+domain: performance
+keywords: [reset, setloadfields, partial-record, load-selection, findset]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Reset and empty SetLoadFields restore a full-row load
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+`SetLoadFields(...)` sticks to the record variable until something clears it. `Reset()` "changes fields select for loading back to all", and `SetLoadFields()` with no arguments does the same. A later `FindSet` or `Get` then materializes every normal field. Agents often place `SetLoadFields` first, then `Reset` to apply new filters, and assume the partial selection survives. It does not.
+
+## Best Practice
+
+Call `Reset` (or empty `SetLoadFields()`) first when the variable must be reused, then call `SetLoadFields` with the fields the next read actually uses, then apply filters and read. After `Reset`, a new `SetLoadFields` is required; the previous list is gone.
+
+See sample: `reset-clears-partial-record-selection.good.al`.
+
+## Anti Pattern
+
+`SetLoadFields(...)` followed by `Reset()` (or by parameterless `SetLoadFields()`) and then `FindSet` without restoring the load list. The filters look correct; the SQL still selects every column.
+
+See sample: `reset-clears-partial-record-selection.bad.al`.

community/knowledge/performance/skip-setloadfields-on-write-and-transferfields.bad.al

@@ -0,0 +1,16 @@
+codeunit 50100 "Skip LoadFields Write Bad"
+{
+    procedure CopyActiveCustomers(var TempCustomer: Record Customer temporary)
+    var
+        Customer: Record Customer;
+    begin
+        // TransferFields requires all fields; partial load forces JIT per row.
+        Customer.SetLoadFields("No.", Name);
+        Customer.SetRange(Blocked, Customer.Blocked::" ");
+        if Customer.FindSet() then
+            repeat
+                TempCustomer.TransferFields(Customer);
+                TempCustomer.Insert();
+            until Customer.Next() = 0;
+    end;
+}

community/knowledge/performance/skip-setloadfields-on-write-and-transferfields.good.al

@@ -0,0 +1,15 @@
+codeunit 50100 "Skip LoadFields Write Good"
+{
+    procedure CopyActiveCustomers(var TempCustomer: Record Customer temporary)
+    var
+        Customer: Record Customer;
+    begin
+        // TransferFields needs all fields; omit SetLoadFields so the initial read loads the full row.
+        Customer.SetRange(Blocked, Customer.Blocked::" ");
+        if Customer.FindSet() then
+            repeat
+                TempCustomer.TransferFields(Customer);
+                TempCustomer.Insert();
+            until Customer.Next() = 0;
+    end;
+}

community/knowledge/performance/skip-setloadfields-on-write-and-transferfields.md

@@ -0,0 +1,28 @@
+---
+bc-version: [all]
+domain: performance
+keywords: [setloadfields, partial-record, jit-load, modify, insert, transferfields, write-path]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Skip SetLoadFields on write and copy paths
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+`SetLoadFields` is a read optimization. The platform's [partial-record usage guidelines](https://learn.microsoft.com/en-us/dynamics365/business-central/dev-itpro/developer/devenv-partial-records#usage-guidelines) list the operations that require every field to already be present: `Insert`, `Delete`, `Rename`, `TransferFields`, and copying a record into a temporary table. When those operations run on a partial record, the platform issues a just-in-time load of the missing fields. That extra round-trip costs more than loading the full row on the original `FindSet` or `Get`. Note: `Modify` itself is **not** in this list — a `Modify(false)` that only touches loaded fields is safe with a partial record.
+
+## Best Practice
+
+Omit `SetLoadFields` on loops whose body performs a documented full-load operation (`Insert`, `Delete`, `Rename`, `TransferFields`, or assignment into a temporary record) on the same record variable, so the initial read already materializes every field those operations need.
+
+See sample: `skip-setloadfields-on-write-and-transferfields.good.al`.
+
+## Anti Pattern
+
+Calling `SetLoadFields` immediately before a `FindSet` whose body performs `Delete`, `Rename`, `TransferFields`, or copies the record into a temporary table. The review signal is a partial-record setup on a record variable that feeds one of these documented full-load operations in the same iteration.
+
+See sample: `skip-setloadfields-on-write-and-transferfields.bad.al`.

community/knowledge/performance/use-dedicated-lookup-pages-not-full-lists.bad.al

@@ -0,0 +1,60 @@
+table 50100 "Campaign Member"
+{
+    Caption = 'Campaign Member';
+    // Full list as lookup runs FactBoxes and extra columns on every dropdown.
+    LookupPageId = Page::"Campaign Member List";
+    DrillDownPageId = Page::"Campaign Member List";
+    DataClassification = CustomerContent;
+
+    fields
+    {
+        field(1; "No."; Code[20]) { }
+        field(2; Name; Text[100]) { }
+        field(3; "Balance (LCY)"; Decimal) { }
+    }
+
+    keys
+    {
+        key(PK; "No.") { Clustered = true; }
+    }
+}
+
+page 50100 "Campaign Member List"
+{
+    PageType = List;
+    SourceTable = "Campaign Member";
+
+    layout
+    {
+        area(content)
+        {
+            repeater(Rows)
+            {
+                field("No."; Rec."No.") { }
+                field(Name; Rec.Name) { }
+                field("Balance (LCY)"; Rec."Balance (LCY)") { }
+            }
+        }
+        area(factboxes)
+        {
+            // Full list carries this FactBox on every dropdown open — expensive.
+            part(Details; "Campaign Member Details FB") { }
+        }
+    }
+}
+
+page 50101 "Campaign Member Details FB"
+{
+    PageType = CardPart;
+    SourceTable = "Campaign Member";
+
+    layout
+    {
+        area(content)
+        {
+            field("No."; Rec."No.") { }
+            field(Name; Rec.Name) { }
+            field("Balance (LCY)"; Rec."Balance (LCY)") { }
+        }
+    }
+}

community/knowledge/performance/use-dedicated-lookup-pages-not-full-lists.good.al

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+table 50100 "Campaign Member"
+{
+    Caption = 'Campaign Member';
+    LookupPageId = Page::"Campaign Member Lookup";
+    DrillDownPageId = Page::"Campaign Member List";
+    DataClassification = CustomerContent;
+
+    fields
+    {
+        field(1; "No."; Code[20]) { }
+        field(2; Name; Text[100]) { }
+        field(3; "Balance (LCY)"; Decimal) { }
+    }
+
+    keys
+    {
+        key(PK; "No.") { Clustered = true; }
+    }
+}
+
+page 50100 "Campaign Member Lookup"
+{
+    PageType = List;
+    SourceTable = "Campaign Member";
+    Caption = 'Campaign Members';
+
+    layout
+    {
+        area(content)
+        {
+            repeater(Rows)
+            {
+                field("No."; Rec."No.") { }
+                field(Name; Rec.Name) { }
+            }
+        }
+    }
+}
+
+page 50101 "Campaign Member List"
+{
+    PageType = List;
+    SourceTable = "Campaign Member";
+
+    layout
+    {
+        area(content)
+        {
+            repeater(Rows)
+            {
+                field("No."; Rec."No.") { }
+                field(Name; Rec.Name) { }
+                field("Balance (LCY)"; Rec."Balance (LCY)") { }
+            }
+        }
+    }
+}

community/knowledge/performance/use-dedicated-lookup-pages-not-full-lists.md

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+---
+bc-version: [all]
+domain: performance
+keywords: [lookuppageid, lookup-page, list-page, factbox, table-relation, dropdown]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Point lookups at a dedicated lookup page, not the full list
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+A `TableRelation` lookup opens the table's `LookupPageId`. If that is the full list page, the lookup runs that page's triggers, FactBoxes, and calculated fields even though the dropdown never shows them. The base application added dedicated Customer, Vendor, and Item lookup pages for this reason. Agents set `LookupPageId` to the main list because it already exists.
+
+## Best Practice
+
+Give master tables a slim lookup page (`PageType = List`, few columns, no FactBoxes, no heavy `OnAfterGetRecord`) and assign it to `LookupPageId`. Keep the full list for `DrillDownPageId` and the role-explorer entry.
+
+See sample: `use-dedicated-lookup-pages-not-full-lists.good.al`.
+
+## Anti Pattern
+
+`LookupPageId = Page::"... List"` on a table that already has (or should have) a lookup page. Opening a field lookup then pays list-page cost. The signal is `LookupPageId` pointing at a page that declares FactBoxes or a wide repeater.
+
+See sample: `use-dedicated-lookup-pages-not-full-lists.bad.al`.

community/knowledge/performance/validate-on-partial-record-forces-jit.bad.al

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+codeunit 50100 "Validate Partial Rec Bad"
+{
+    procedure UppercaseUsCustomerNames()
+    var
+        Customer: Record Customer;
+    begin
+        Customer.SetLoadFields(Name);
+        Customer.SetRange("Country/Region Code", 'US');
+        if Customer.FindSet(true) then
+            repeat
+                // Validate touches other fields and TableRelation reads; JIT undoes the partial load.
+                Customer.Validate(Name, UpperCase(Customer.Name));
+                Customer.Modify(false);
+            until Customer.Next() = 0;
+    end;
+}

community/knowledge/performance/validate-on-partial-record-forces-jit.good.al

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+codeunit 50100 "Validate Partial Rec Good"
+{
+    procedure UppercaseUsCustomerNames()
+    var
+        Customer: Record Customer;
+    begin
+        // Include every field that Name.OnValidate reads so the runtime never JIT-loads.
+        Customer.SetLoadFields(Name, "Search Name");
+        Customer.SetRange("Country/Region Code", 'US');
+        if Customer.FindSet(true) then
+            repeat
+                Customer.Validate(Name, UpperCase(Customer.Name));
+                Customer.Modify(false);
+            until Customer.Next() = 0;
+    end;
+}

community/knowledge/performance/validate-on-partial-record-forces-jit.md

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+---
+bc-version: [all]
+domain: performance
+keywords: [validate, setloadfields, jit-load, table-relation, onvalidate, partial-record]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Validate on a partial record forces JIT loads
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+`Validate` runs the field's `OnValidate` trigger and TableRelation lookups. Those code paths routinely touch other fields on the same record. On a partial row those extra fields are not loaded, so the platform JIT-loads them — often the rest of the row — plus any related-table reads the trigger performs. Distinct from `skip-setloadfields-on-write-and-transferfields.md`: the write may be `Modify(false)`; `Validate` is what blows the partial load. Agents that combine `SetLoadFields` with `Validate` in a loop produce slower code than an unoptimized assignment.
+
+## Best Practice
+
+In a partial-record loop, assign fields directly when trigger side effects are not required. If `Validate` is required, do not use `SetLoadFields` on that iterator, or `AddLoadFields` every field the validate path can touch before the read.
+
+See sample: `validate-on-partial-record-forces-jit.good.al`.
+
+## Anti Pattern
+
+`SetLoadFields` on a handful of columns, then `Validate` inside the loop. The load list looks optimal; runtime JIT and TableRelation I/O dominate. The signal is `Validate(` on a record that still has a `SetLoadFields` in the same procedure.
+
+See sample: `validate-on-partial-record-forces-jit.bad.al`.