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Fast calculations

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Power Fx expressions are powerful and do many background calculations for you automatically. While Power Fx automates many things for you, it's possible to fine-tune your calculations so there as fast as possible.

Data retrieval

Use Explicit column selection

The Explicit Column Selection (ECS) feature is enabled by default for all new apps. If it isn't enabled for your app, you should enable it. ECS automatically reduces the number of columns retrieved to only the ones that are used in the application. If ECS isn't enabled, you might be retrieving more data than you need, which can affect performance. Occasionally, when an app pulls data in through collections, the original lineage or source of a column can be lost. We don't know if it’s being used and we drop it using ECS. You can usually force ECS to work for a missing column by using the PowerFx expression ShowColumns after a collection reference or by using it in a control.

Use images on galleries, tables, and forms carefully

Use Dataverse thumbnail versions of images for galleries and tables. Dataverse thumbnails are small about 1 kilobyte and are stored inline as part of the record, and are useful and fast for display on controls that show collections. All other image references including all SharePoint images require a separate call and shouldn't be placed on a gallery or table. Place images that require a separate call on detail forms. Consider never showing a full image by default. Full detailed images can be useful and important to users. However, you can make these images available to users through an explicit user action, for example, a button or navigation to a separate page. SharePoint has a range of intermediate sized images you can use for use on a form short of the full image. Dataverse only has two sizes: Thumbnail and Full.

Calculations

Split up formulas with App.formula

The use of App.formulas and named formulas can help with the speed of app load and page navigation because it allows Power Fx to decide when to evaluate a formula. That means it doesn't have to necessarily evaluate it in OnStart. In addition, named formulas can generally help speed as well. In particular if you have a long script, breaking it up into named formulas allow for more efficient calculations as Power Fx can schedule the work and it enables reuse. For more information, see App formulas.

Use Concurrent

Use the Concurrent function to allow formulas to be executed at the same time. Carefully choose where concurrent is used. It can provide some modest speed ups but if you're running items that depend on each other it can cause timing and throttling issues.

Defer significant updates to a nonblocking UI step

Large updates to a data source may take a while to complete. But users expect the UI to return control to them quickly. Tasks may be either sequential where the update must finish before the user can take another actions or asynchronous (the update can finish separate of user actions.)

An example of a time-consuming synchronous task is confirming a seat at a concert. For most time-consuming synchronous tasks like this, it’s common to put up a progress bar. This UI actually blocks the user but ensures that the task is complete before other UI elements are updated. This approach may not work for your application. Businesses normally handle longer sequential steps as an explicit business step. You're approved to go the next step via a business process signal. An example is an approval. An approval may come quickly or may be delayed. In the UI you can signal that the process is complete several ways. You can enable a button, show a message, send e-mail, or enable a part of the UI such as a menu item.

An example of an asynchronous task is the completion of an order. A customer updates an order basket, works through their order and then places the order. But several updates must happen before the customer is given a confirmed ship date. In this example, the Ship Date isn't something you can easily provide right away. , you can defer this part of the update to an e-mail that is sent to the customer later.

For synchronous tasks, you'll often use the code in Power Apps for UI blocking tasks. For instance, the code waits until it gets a return value and then releases the progress bar. It is best to minimize these types of situations. But for tasks that use an explicit business step or asynchronous tasks it's common to use an external service to complete the task such as a Dataverse action, stored procedure, or a Power Automate flow.

Place 'ForAll' appropriately

If you have an expression with ForAll and collect that looks like this:

ForAll(x, Collect(y, { … }))

Then, invert this to

Collect(y, ForAll(x, { … }))

In the first pattern, any dependent rule on collection y is notified of changes and evaluated for each iteration of x. In the second pattern, these rules are only evaluated once.

Consider avoiding references to Gallery.AllItems

When working with Power Apps, it’s best to avoid referencing Gallery.AllItems unless you need out user values. This is because every time AllItems is read, a new output table is generated. Instead, use Gallery.AllItemsCount if you just want to know how many items are loaded.

Carefully use Gallery.TemplateSize

To ensure that flexible-height galleries are rendered correctly, it’s important to set a reasonable default size. Initially, we try to render as many rows as possible based on this value. If you set the default size to 0, we try to render everything, except for a few edge cases. If you’re using a formula, make sure to set a minimum value for when the formula might evaluate to 0. For example, you could use Max (20, varFoo + rectBar.Height). This way, if varFoo and rectBar.Height aren’t yet available, we at least use a reasonable value of 20.

There's one second delay before the changes is detected, which allows you to complete the typing instead of detecting the changes for every typing.