vals.hs

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE NumericUnderscores #-}
module Main where

import           Database.PostgreSQL.Simple
import           Control.Monad
import qualified Data.Text                     as Text
import           Data.Time
import qualified GHC.Clock                     as Clock
import qualified Text.Printf                   as Printf

main :: IO ()
main = do
  conn <- connectPostgreSQL "port=5435 dbname=postgres"
  execute_ conn "drop table if exists foo;"
  putStrLn "creating table"
  execute_ conn "create table foo (id serial4, name varchar);"
  putStrLn ""

  let numRows = 20_000_000
  putStrLn $ "inserting " <> show numRows <> " rows"
  putStrLn ""

  execute_ conn
           "insert into foo(name) select * from generate_series(1, 20000000)"

  putStrLn "length of foo"
  query_ @(Only Int) conn "select count(*) from foo;" >>= print
  putStrLn ""

  putStrLn "print top 5 rows"
  query_ @(Int, Maybe Text.Text) conn "select * from foo limit 5"
    >>= mapM_ print
  putStrLn ""

  putStrLn "start alter table"
  timeBefore <- Clock.getMonotonicTime
  void $ execute_ conn "ALTER TABLE foo ALTER COLUMN id SET DATA TYPE bigint"
  timeAfter <- Clock.getMonotonicTime

  putStrLn ""
  let duration = timeAfter - timeBefore

  putStrLn $ Printf.printf "duration %.3f" duration