postgresql-resilient (empty) → 0.1.0.0

raw patch · 5 files changed

+382/−0 lines, 5 filesdep +basedep +exceptionsdep +postgresql-simplesetup-changed

Dependencies added: base, exceptions, postgresql-simple

Files

• CHANGELOG.md +5/−0
• LICENSE +202/−0
• Setup.hs +2/−0
• postgresql-resilient.cabal +22/−0
• src/Database/PostgreSQL/Resilient.hs +151/−0

@@ -0,0 +1,5 @@+# Revision history for postgresql-resilient++## 0.1.0.0 -- YYYY-mm-dd++* First version. Released on an unsuspecting world.

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@@ -0,0 +1,2 @@+import Distribution.Simple+main = defaultMain

@@ -0,0 +1,22 @@+cabal-version:       2.4++name:                postgresql-resilient+version:             0.1.0.0+synopsis:            Automatic re-connection support for PostgreSQL+description:         PostgreSQL single-connection pool with automatic re-connection support, built on top of postgresql-simple.+license:             Apache-2.0+license-file:        LICENSE+author:              Gabriel Volpe+maintainer:          volpegabriel@gmail.com+category:            Database+build-type:          Simple+extra-source-files:  CHANGELOG.md++library+  exposed-modules:     Database.PostgreSQL.Resilient+  build-depends:       base                  >= 4.13.0 && < 4.14+                     , exceptions            >= 0.10.4 && < 0.11+                     , postgresql-simple     >= 0.6.2 && < 0.7+  hs-source-dirs:      src+  default-language:    Haskell2010+  ghc-options:         -Wall

@@ -0,0 +1,151 @@+{-# LANGUAGE DeriveAnyClass, DerivingVia #-}+{-# LANGUAGE FlexibleContexts, ScopedTypeVariables #-}+{-# LANGUAGE OverloadedStrings, RankNTypes #-}++{-|+Module      : Database.PostgreSQL.Resilient+Description : PostgreSQL single-connection pool with automatic reconnection support, built on top of postgresql-simple.+License     : Apache-2.0+Maintainer  : volpegabriel@gmail.com+Stability   : experimental++The `withResilientConnection` function gives us a `ResilientConnection` from which we can always get a health connection, while automatic reconnection with retries and exponential back-offs are being handled in the background.++@+import           Database.PostgreSQL.Resilient+import qualified Database.PostgreSQL.Simple    as P++withResilientConnection defaultResilientSettings logHandler connectInfo $ \pool ->+  (conn :: P.Connection) <- getConnection pool+  res <- P.query_ conn "SELECT * FROM foo"+  putStrLn $ show res++logHandler :: String -> IO ()+logHandler = putStrLn++connectInfo :: P.ConnectInfo+connectInfo = P.ConnectInfo+  { P.connectHost     = "localhost"+  , P.connectPort     = 5432+  , P.connectUser     = "postgres"+  , P.connectPassword = ""+  , P.connectDatabase = "store"+  }++defaultResilientSettings :: ResilientSettings+defaultResilientSettings = ResilientSettings+  { healthCheckEvery     = 3+  , exponentialBackoffThreshold = 10+  }+@+-}+module Database.PostgreSQL.Resilient+  ( ResilientConnection(..)+  , ResilientSettings(..)+  , Seconds+  , withResilientConnection+  , defaultResilientSettings+  )+where++import           Control.Concurrent             ( forkIO+                                                , killThread+                                                , threadDelay+                                                )+import           Control.Concurrent.MVar+import           Control.Monad                  ( forever )+import           Control.Monad.Catch+import           Data.IORef+import           Data.Functor                   ( void )+import           Data.Maybe                     ( fromJust )+import qualified Database.PostgreSQL.Simple    as P+import           GHC.IO.Exception+import           Prelude                 hiding ( init )++data DBConnectionError = DBConnectionError deriving (Exception, Show)++{- | Single connection pool with built-in reconnection -}+data ResilientConnection m = ResilientConnection+  { getConnection :: m P.Connection -- ^ Get the latest healthy connection.+  }++type LogHandler = String -> IO ()++{- | Represents amount of seconds -}+newtype Seconds = Seconds Int+  deriving (Eq, Num, Ord, Show) via Int++{- | The resilient settings -}+data ResilientSettings = ResilientSettings+  { healthCheckEvery :: Seconds            -- ^ How often to check the connection status.+  , exponentialBackoffThreshold :: Seconds -- ^ After this threshold, stop the exponential back-off.+  } deriving Show++{- | Default resilient settings -}+defaultResilientSettings :: ResilientSettings+defaultResilientSettings =+  ResilientSettings { healthCheckEvery = 3, exponentialBackoffThreshold = 10 }++{- | Sleep for n amount of seconds -}+sleep :: Seconds -> IO ()+sleep (Seconds n) = threadDelay (n * 1000000)++healthCheck :: LogHandler -> P.Connection -> IO ()+healthCheck logger conn = do+  (res :: [P.Only String]) <- P.query_ conn "SELECT version();"+  logger $ show res++{- | Returns a `ResilientConnection` from which you can always acquire the latest connection available.+ -+ - Reconnections with configurable retries and exponential back-offs as well as closing the connection once done using it (guaranteed by `bracket`) are too handled by this function.+ - -}+withResilientConnection+  :: forall a+   . ResilientSettings+  -> LogHandler+  -> P.ConnectInfo+  -> (ResilientConnection IO -> IO a)+  -> IO a+withResilientConnection settings logger info f = do+  ((,) <$> newIORef Nothing <*> newEmptyMVar) >>= \(connRef, signal) ->+    let shutdown = readMVar signal >>= killThread -- ends keep-alive process+        pool     = ResilientConnection (fromJust <$> readIORef connRef)+        ka       = keepAlive (reconnect connRef) pool+        init     = acquire connRef >> ka >>= putMVar signal+    in  bracket (pool <$ init) (release shutdown) f+ where+  acquire ref = do+    logger "Connecting to PostgreSQL"+    conn <- P.connect info+    conn <$ atomicWriteIORef ref (Just conn)++  release shutdown pool = do+    logger "Closing PostgreSQL connection"+    conn <- getConnection pool+    P.close conn+    logger "Shutdown PostgreSQL reconnection process"+    shutdown++  clean conn = do+    logger "Closing no longer valid PostgreSQL connection"+    P.close conn++  reconnect ref n = catch (void $ acquire ref) $ \(e :: SomeException) ->+    logger (retries e) >> sleep n >> reconnect ref n'+   where+    retries e = show e <> "\n >>> Retrying in " <> show n <> " seconds."+    t  = exponentialBackoffThreshold settings+    n' = if n >= t then t else n * 2++  keepAlive rec pool = forkIO $ forever $ do+    sleep $ healthCheckEvery settings+    logger "Checking PostgreSQL connection status"+    conn <- getConnection pool+    catch+      (healthCheck logger conn)+      (\(e :: IOError) ->+        -- OtherError is thrown on every internal libpq error such as connection error+        if ioe_type e == ResourceVanished || ioe_type e == OtherError+          then clean conn >> rec 1+          else logger (show e) >> throwM DBConnectionError+      )