Delegation and Variable/Collections

[larivibi]

I can clearly see the benefits of delegation when I populate a Gallery. The queries are fast to comeback with lots of data. But I am unable to store a "delegable" query into a variable (local or global) or into a collection. 
I have set the non delegable limit to 3 items, so I can see if delegation works.

The exact same formula works with delegation when using the Items property of a Gallery (it populates the gallery with 55 items), but only populates a collection or variable with 3 items (non delegable limit I set).

Is it impossible to store delegable queries into variables/collections ?

[RandyHayes]

@larivibi 

Galleries perform their gathering of information differently than trying to put information in a collection.

If your record limit is set to 3 then you will only get 3 records on any particular formula...except in the case of a Gallery.  They "page" themselves differently.

However, your post is more in regard to record limit than it is to delegation.  Delegation is the factor of sending a "query" to the datasource to get results that the datasource can handle on its own.

Record limit has only to do with the maximum number of results you get back.

So if your record limit is set to 3, you will never get more than 3 records in return.  So, if you delegate a filter, you will only get 3 records back.

As for the variables and collections - unless there is some specific need for a duplicate snapshot of your data, avoid them.

I hope this is helpful for you.

[larivibi]

Thank You for the info,

just to be sure, this here :

...is not only setting limit for non delegable queries, but also the limit of records obtained by a delegable query when stored into a variable or collection?
Do I understand correctly ?

[RandyHayes · Accepted solution]

@larivibi 

That is correct.  It sets the maximum number of records in the session tables and thus the maximum number of records you can retrieve at one time - from ANY query - delegable or not.

To get a better understanding on the limit and delegation, I like to use the truck scenario.   

Let's say you have a truck that can only carry 10 boxes (record limit).  If you go to a store (datasource), you can return with 10 boxes.  If you ask the clerk to give you all the boxes with a blue label on the outside, they can easily do it (delegable query).  If they have 20 boxes with blue labels, they will give you the first 10 they find because you can only handle 10 boxes (delegable query with record limit).

If you ask them for all the boxes with blue lamps in them, they tell you - "we can't open the boxes and look", but we can give you the 10 boxes you can carry with you and then you can open them and see (non-delegable query with record limit).  So, you take your 10 boxes and open them to look and find that only 3 of them had blue lamps.  SO...you have 3 boxes with blue lamps - that is your result. 
The problem with a non-delegable query (as you know) is that YES, you got 3 blue lamps and you tell whoever you are getting them for that there are 3 blue lamps...but in reality the store still had a lot of other boxes that might also have blue lamps in them.

So, the obvious answer that everyone goes for is - just bump up the record limit to 2000 and cross your fingers.  Well, the real answer is to design your app and data to not only be delegable, but also to limit your records to only the amount you really need in the app.  Because, otherwise you are impacting performance loading up 2000 "boxes" into your truck all the time when you only needed 10 of them.

Hopefully that is clear and helpful for you.

EDIT: Oh, and again, the way the records come back for Galleries is different as the Gallery "pages" the results differently with the record limits and query.

[larivibi]

Wow! This should be in the PowerApps documentation! Very clear explanation. Thank you very much.

I tought of a Solution yesterday to keep the information flowing fast, but I am not sure it is a good one for best practice). Surely you can light my way on this one:

I have an equipments table as a Sharepoint list that I connect to (700 records so far, but will grow by about a hundred items a year) thus the need for delegation.
When I reach for the SP list to show in a gallery, delegation works because even though my query limit is only 3 (for testing purposes). I get all the items I ask for (filter through a simplet text column). The same thing did not work if trying to store a query into a variable or a collection. I now know why, thanks to your clear explanation 🙂
First challenge seemed settled. The second step was to show distinct equipment (and not all instances of every type of equipment).
With Distinct, delegation did not work (only 3 records returned in the gallery). Since I thought variables and Galleries would not be delegable, I created another Gallery that would fetch the first gallery and only show distinct values of the first Gallery. I thought by hiding that first "reference" gallery, I was being clever. 

It works really well, but I have a feeling that it is not a good practice (hiding a gallery, that is).

I would really appreciate your wisdom on this. What would you do in that situation ?

By the way, if you ever have some more time later, I would be interested to know how the Galleries function for gathering the information.

[RandyHayes · Accepted solution]

@larivibi 

I'll start with the later part - Galleries were designed (IMO) around the fact that people seem to want to show thousands of records in a gallery - because their users really want to scroll through a lot of records to find what they want (sarcasm).  So, this causes issues with performance because not only does the app need to get all the data, but the gallery needs to render it all.  That is a pretty big memory footprint.  So, they made them to page on their own.  They will get a certain number of records first and then as the user scrolls down, continue to get the additional.  This minimized the initial performance issue and the memory issue.  So, they have that little gem in them.  It can be a blessing and a curse depending on how you use the Gallery.

For example, using your approach to having a Gallery be a "sub gatherer" in order to do a Distinct on it to get what you want (because yes, Distinct is not delegable).  So, let's say you have 2000 records in your datasource.  If you set the Gallery to that datasource to get the records and then do a Distinct on the AllItems of the Gallery, then you will run into problems because the Gallery will not have loaded all of the records...it has to page them on demand.  How do you demand them...you have to scroll to the bottom until it is no longer gathering new records.  This is problematic because you either have to have the user scroll it, or, if it is hidden, then you need to scroll it by selecting the last record with the Select function (select for a Gallery lets you not only select the gallery, but also a row).  The problem is...you need to specify the row - the last one.  But how do you know what number that is??  Well, you could CountRows on the datasource to get the number of rows - BUT, CountRows is not delegable!!  So, in your case, you would only count rows of 3.

The reality is that to do delegation properly and handle situations like this, you really have to think from the data side of things.  If you are using SQL for example, you can offload a lot of the non delegable actions into views.  Example, you can get the distinct in a view and then just get that view in your app (of course with 3 records as your limit, you'll still only get 3 records).  But, based on the above Gallery scenario, you could also have a view that returns the count of all the distinct...so you could select the last row in the gallery and have them all.

In the case of SharePoint, you have to plan for these things.  Planning around this is done in a few ways.  One would be to utilize PowerAutomate to create a separate list of all the distinct values.  You could also do it in PowerApps itself, but this is a good job for a flow.  Then, you will have a list with just the distinct values to work from and not need to issue the non-delegable Distinct function.  

How do you get a record count...well, you can't.  But, you can again plan around it with a flow.  If you have another list with even just a single record and a column for each data list that you are interested in and a numeric count of the records in those lists, then you can have flow fill in the current count of records and your app can just refresh that datasource and get the record count.

There are a lot of little ways to plan around delegation issues and record limits.  Most of it becomes very specific to the scenario as opposed to "do it like this all the time".  

As for the documentation...yes, there is a LOT of details missing in them about these situations.  I think they just left it up to the forum to fill in the blanks 😀

Hopefully all clear and helpful for you.

[larivibi]

Again, thank you for the clear and detailed views you have here!

Feeling Enlighted

[gjgiraldo]

if you use filter for example doesnt depends of the limit in power apps, the limit starts when you use not delegable functions.

another thing , if you save the filter in a collection or global variable , you depends of the limit .