diff --git a/CHANGELOG.md b/CHANGELOG.md new file mode 100644 --- /dev/null +++ b/CHANGELOG.md @@ -0,0 +1,5 @@ +# Revision history for postgresql-resilient + +## 0.1.0.0 -- YYYY-mm-dd + +* First version. Released on an unsuspecting world. diff --git a/LICENSE b/LICENSE new file mode 100644 --- /dev/null +++ b/LICENSE @@ -0,0 +1,202 @@ + + Apache License + Version 2.0, January 2004 + http://www.apache.org/licenses/ + + TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + + 1. Definitions. + + "License" shall mean the terms and conditions for use, reproduction, + and distribution as defined by Sections 1 through 9 of this document. + + "Licensor" shall mean the copyright owner or entity authorized by + the copyright owner that is granting the License. + + "Legal Entity" shall mean the union of the acting entity and all + other entities that control, are controlled by, or are under common + control with that entity. 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new file mode 100644 --- /dev/null +++ b/postgresql-resilient.cabal @@ -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 diff --git a/src/Database/PostgreSQL/Resilient.hs b/src/Database/PostgreSQL/Resilient.hs new file mode 100644 --- /dev/null +++ b/src/Database/PostgreSQL/Resilient.hs @@ -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 + )