Cannot disconnect connections in shiny app using pool package - r

Question

I have my shiny app in AWS ubuntu server attached with mysql database, my app doesnot work sometimes when number of database connection exceeded(16 new connections). I tried several ways from various sources in internet but not able to get the required solution.
Furthure i am also getting warning you have leaked pool object . I am attaching the sample code.
library("shiny")
library("shinydashboard")
library("pool")
library(ggplot2)
library("DBI")
library(plotly)
pool <- dbPool(drv = RMySQL::MySQL(),dbname = "db",host = "database.cw5east-2.rds.amazonaws.com",username = "host",password = "host", port = 3306)
mychoices = dbGetQuery(pool,"select available_scenario from scenario_name;")
ui <- (fluidPage(
titlePanel("Demonstration of renderUI in shiny - Dymanically creating the tabs based on user inputs"),
sidebarLayout(
sidebarPanel(
selectInput(inputId = 'n', "available scenarios", choices = mychoices, multiple = TRUE),
verbatimTextOutput("selected")
),
mainPanel(
plotOutput('Cost'),
uiOutput('tabs')
)
)
))
server <- (function(input,output,session){
output$tabs = renderUI({
par(mfrow = c(2, 2))
if(!is.null(input$n)){
x <- input$n
y <- length(x)
z <- dbGetQuery(pool,paste0("select scenario_key from scenario_name where available_scenario = '",x[y],"'"))
frame <- dbGetQuery(pool,paste0("select x,price from plot1 where scenario_key ='",z,"'"))
frame1 <- dbGetQuery(pool,paste0("select obj,runs from plot2 where scenario_key ='",z,"'"))
frame2 <- dbGetQuery(pool,paste0("select V1,V2,V3 from tableee where scenario_key ='",z,"'"))
runs <- dbGetQuery(pool,paste0(" select count(*) from plot2 where scenario_key ='",z,"'"))
b<-dbGetQuery(pool, paste0("select scenario_key from scenario_name where available_scenario = '",input$n,"'"))
Tabs <- lapply(paste("Scenario name:", input$n, sep=" "), tabPanel,
renderPlotly({
ggplot(frame, aes(x=x,y=price,fill=price)) + # basic graphical object
geom_col(width = 0.3)+
#geom_bar(position = 'dodge',stat = "identity")+ # first layer
xlab(NULL)+ylab("Price in USD")+
geom_text(aes(label=price),size=5,position=position_dodge(width=0.9), vjust=-0.25)+
theme_minimal()+
theme(axis.text = element_text(size = 12),
axis.title = element_text(size=16),
axis.text.y =element_text(angle = 90,hjust = 1))
}),
renderPlotly({
ggplot(frame1,aes(x=runs,y=obj))+
geom_col(width=0.3,fill='orangered')+
geom_hline(aes(yintercept=mean(obj,na.rm = T),color="Mean"),linetype='dashed',size=1)+
scale_color_manual(values = "blue")+
labs(x= 'Day Number',y='Reveneue in USD',color=NULL)+
theme_minimal()+theme(axis.text = element_text(size = 12),
axis.title = element_text(size=16),
axis.text.y= element_text(angle = 90,hjust = 1) )
}),
DT::renderDataTable({
frame2
},colnames=c('Day','Total Wt(kg)','Total Pcs','Revenue($)')
)
)
do.call(tabsetPanel, Tabs)}
})
})
shinyApp(ui, server)