using session$onsessionend to disconnect rshiny app from the mysql server - mysql

Question

I obtained this code from R Shiny Gallery here:http://shiny.rstudio.com/gallery/reactive-poll-and-file-reader.html
function(input, output, session) {
# Create a random name for the log file
logfilename <- paste0('logfile',
floor(runif(1, 1e+05, 1e+06 - 1)),
'.txt')
# ============================================================
# This part of the code writes to the log file every second.
# Writing to the file could be done by an external process.
# In this example, we'll write to the file from inside the app.
logwriter <- observe({
# Invalidate this observer every second (1000 milliseconds)
invalidateLater(1000, session)
# Clear log file if more than 10 entries
if (file.exists(logfilename) &&
length(readLines(logfilename)) > 10) {
unlink(logfilename)
}
# Add an entry to the log file
cat(as.character(Sys.time()), '\n', file = logfilename,
append = TRUE)
})
# When the client ends the session, suspend the observer and
# remove the log file.
session$onSessionEnded(function() {
logwriter$suspend()
unlink(logfilename)
})
# ============================================================
# This part of the code monitors the file for changes once per
# 0.5 second (500 milliseconds).
fileReaderData <- reactiveFileReader(500, session,
logfilename, readLines)
output$fileReaderText <- renderText({
# Read the text, and make it a consistent number of lines so
# that the output box doesn't grow in height.
text <- fileReaderData()
length(text) <- 14
text[is.na(text)] <- ""
paste(text, collapse = '\n')
})
# ============================================================
# This part of the code monitors the file for changes once
# every four seconds.
pollData <- reactivePoll(4000, session,
# This function returns the time that the logfile was last
# modified
checkFunc = function() {
if (file.exists(logfilename))
file.info(logfilename)$mtime[1]
else
""
},
# This function returns the content of the logfile
valueFunc = function() {
readLines(logfilename)
}
)
output$pollText <- renderText({
# Read the text, and make it a consistent number of lines so
# that the output box doesn't grow in height.
text <- pollData()
length(text) <- 14
text[is.na(text)] <- ""
paste(text, collapse = '\n')
})
}
If you look closely at the code above, you will see this segment:
# When the client ends the session, suspend the observer and
# remove the log file.
session$onSessionEnded(function() {
logwriter$suspend()
unlink(logfilename)
})
I want to tweak that code in my shiny app to disconnect my MySQL server from my shiny app. Like this:
session$onSessionEnded(function() {
dbDisconnect(con)
})
I want to do this to ensure this warning message: "Unable to connect to database: Too many connections"
Would that ensure connections are freed up for other users? (I had a problem with my app because so many users were on and did not disconnect, leaving no available spot on the server.)