bindCache + validate long running query

shiny
1

Hi all,
I'm trying to implement bindCache to make my shiny app faster. There is a long running data query that sometimes fails. I am using validate(need(..)) to check to see if it fails and wait, but bindCache still seems to write. This means if I want to try it again, the cache kicks in with the error message from the need(). Is there a better workflow for this to let the app try again if there's an error? Or alternatively, can I invalidate the cache easily for a particular key? A dummy example of bindCache still writing with need is below.

library(shiny)
library(tidyverse)
shinyOptions(cache = cachem::cache_disk("cache"), max_age = 60 * 60 * 24)

# Define UI for application that draws a histogram
ui <- fluidPage(

    # Application title
    titlePanel("Old Faithful Geyser Data"),

    # Sidebar with a slider input for number of bins
    sidebarLayout(
        sidebarPanel(
            sliderInput("bins",
                        "Number of bins:",
                        min = 1,
                        max = 50,
                        value = 30)
        ),

        # Show a plot of the generated distribution
        mainPanel(
           plotOutput("distPlot")
        )
    )
)

# Define server logic required to draw a histogram
server <- function(input, output) {

    output$distPlot <- renderPlot({
        validate(
            need(1 == 2, 'hmm')
        )

        print("hi")
        # generate bins based on input$bins from ui.R
        x    <- faithful[, 2]
        bins <- seq(min(x), max(x), length.out = input$bins + 1)

        # draw the histogram with the specified number of bins
        hist(x, breaks = bins, col = 'darkgray', border = 'white')
    }) %>% bindCache(input$bins)
}

# Run the application
shinyApp(ui = ui, server = server)
Shiny applications not supported in static R Markdown documents

Created on 2021-06-14 by the reprex package (v2.0.0)

2

I think this is a good solution.

library(shiny)
library(tidyverse)
ch <- cachem::cache_disk("cache")
ch$reset()
shinyOptions(cache =ch , max_age = 60 * 60 * 24)

# Define UI for application that draws a histogram
ui <- fluidPage(
  
  # Application title
  titlePanel("Old Faithful Geyser Data"),
  
  # Sidebar with a slider input for number of bins
  sidebarLayout(
    sidebarPanel(
      sliderInput("bins",
                  "Number of bins:",
                  min = 1,
                  max = 50,
                  value = 30),
      shiny::checkboxInput("condition","Validation Condition",
                           value=FALSE)
    ),
    
    # Show a plot of the generated distribution
    mainPanel(
      plotOutput("distPlot")
    )
  )
)

# Define server logic required to draw a histogram
server <- function(input, output) {
  
  validation_check1 <- reactive({
    TRUE == input$condition
  })
  output$distPlot <- renderPlot({
 
    validate(need(validation_check1(),"hmm"))
    req(validation_check1())
    
    Sys.sleep(1)
    print("hi")
    # generate bins based on input$bins from ui.R
    x    <- faithful[, 2]
    bins <- seq(min(x), max(x), length.out = input$bins + 1)
    
    # draw the histogram with the specified number of bins
    hist(x, breaks = bins, col = 'darkgray', border = 'white')
  }) %>% bindCache(input$bins,validation_check1())
}

# Run the application
shinyApp(ui = ui, server = server)
3

Thanks for the suggestion. So essentially pull out the validation and use that as a key for the cache as well. I think this should work. I am curious if there's a way to either avoid caching entirely, or able to get the cache key and delete it just for my own curiosity. Thanks again!

4

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