Data.MultiPool.Persist.Postgresql

Documentation

initMultiPool :: (MonadLogger m, MonadUnliftIO m) => ConnectionString -> Int -> [(InstanceName SqlReadBackend, ConnectionString, Int)] -> m (MultiPool SqlBackend)

initMultiPool'

Arguments

:: (MonadLogger m, MonadUnliftIO m)

=> (MultiPool SqlBackend -> IO (Maybe (InstanceName SqlReadBackend)))

-> ConnectionString

Primary connection string

-> Int

Max number of connections to primary instance

-> [(InstanceName SqlReadBackend, ConnectionString, Int)]

Replica connection details

-> m (MultiPool SqlBackend)

runReadCurrent :: MonadUnliftIO m => MultiPool SqlBackend -> HashMap (InstanceName SqlReadBackend) LSN -> LSN -> ReaderT SqlReadBackend m a -> m a

Performs a read on the first replica found that sufficiently up-to-date with the given LSN. This function can be combined with gatherLSNs and some sort of caching mechanism to provide a simple way to scale out reads. An great article on this concept can be found here

If no replica is up-to-date with the given LSN, the primary instance will be used to run the query.

getLastLSN :: MonadIO m => ReaderT SqlReadBackend m LSN

gatherLSNs :: MonadUnliftIO m => MultiPool SqlBackend -> m (HashMap (InstanceName SqlReadBackend) LSN)