How to deal with the slow Appian grid selection validation?

Can you paste the SAIL code you have? There is an easy way in SAIL to only allow single row selection. Some reasons why the section might be slow:

1. Your record type is referencing a database view or large table

2. Your grid is querying extra columns from the database

Thank you Danny but I do not need to allow single row selection.
I have to deal with muli-selection, but each time I select row, I have to wait 2 seconds.

Without posting a sample of your SAIL code like Danny mentioned, we can't really help you without just guessing.

Yes, you're right, here is my sample code:
In my example, you can select some lines while total value of rows is less or equal to 50.

So, if you select the "make4" row, you can not select another row (unless you unselect this row).
But, if you click very quickly and successively on these 3 rows : "make4", "make3", "make2", you will obtain the selection like the picture below : "make3" and "make4" rows are wrongly selected and the total is 70, so it should not be possible.

In reference of what Danny said, you can easier testing this using a database view or large table, with a lot more grid columns.

a!localVariables(
  local!saveSelectedVehicles: null,
  local!selection: ri!selectedVehicleIds,
  local!valMaxAuto: 50, 

  a!sectionLayout(
    contents: {
      a!columnsLayout(
        columns: {
          a!columnLayout(
            contents: {
              a!cardLayout(
                contents: {
                  a!gridField(
                    label: "Read-only Grid",
                    labelPosition: "ABOVE",
                    data: ri!vehicles,
                    columns: {
                      a!gridColumn(
                        label: "Make",
                        value: fv!row.make
                      ),
                      a!gridColumn(
                        label: "Model",
                        value: fv!row.model
                      ),
                      a!gridColumn(
                        label: "Value",
                        value: fv!row.value
                      ),
                    },
                    selectable: true,
                    selectionStyle: "ROW_HIGHLIGHT",
                    selectionValue: local!selection,
                    selectionSaveInto: {
                      local!selection,
                      a!save(
                        ri!selectedVehicles, append(
                          ri!selectedVehicles, cast(
                            'type!{urn:com:appian:types:cjt2}CJT2_Vehicles?list',
                            fv!selectedRows
                          )
                        )
                      ),
                      a!save(
                        ri!selectedVehicles, 
                        difference(
                          ri!selectedVehicles, 
                          cast(
                            'type!{urn:com:appian:types:cjt2}CJT2_Vehicles?list',
                            fv!deselectedRows
                          )
                        )
                      ),

                      /* Manage selection acceptance */
                      a!localVariables(
                        local!maxValueAccepted: if (not(isnull(ri!selectedVehicles)),
                        sum(
                          a!forEach(
                            items: ri!selectedVehicles,
                            expression: fv!item.value
                          )
                        ),
                        0
                        ),

                        if (local!maxValueAccepted > local!valMaxAuto,
                        {
                          a!save(local!selection, remove(local!selection, length(local!selection))), 
                          a!save(ri!selectedVehicles, remove(ri!selectedVehicles, length(ri!selectedVehicles))),
                        },
                        null
                        )
                      ),

                      a!save(ri!selectedVehicleIds, local!selection)

                    },
                    validations: {}
                  )
                },
                height: "AUTO",
                style: "NONE",
                marginBelow: "STANDARD"
              ),

            }
          ),
          a!columnLayout(
            contents: {}
          )
        }
      ),
      a!paragraphField(
        label:"ri!selectedVehicle",
        value: ri!selectedVehicles
      )
    },
    showWhen: true
  )
)

One potential issue here is that in your grid selection saveInto, you're doing maybe 5 or 6 consecutive operations for every single click, when you could probably accomplish the same thing in 1 or 2 operations.

One potential issue here is that in your grid selection saveInto, you're doing maybe 5 or 6 consecutive operations for every single click, when you could probably accomplish the same thing in 1 or 2 operations.