Hasql.Pool

Documentation

data Pool

A pool of open DB connections.

type Settings = (PoolSize, ResidenceTimeout, Settings)

Settings of the connection pool. Consist of:

• Pool-size.
• Timeout. An amount of time for which an unused resource is kept open. The smallest acceptable value is 0.5 seconds.
• Connection settings.

data UsageError

A union over the connection establishment error and the session error.

Constructors

ConnectionError ConnectionError

SessionError QueryError

Instances

Show UsageError

Defined in Hasql.Pool

Methods

showsPrec :: Int -> UsageError -> ShowS

show :: UsageError -> String

showList :: [UsageError] -> ShowS

Eq UsageError

Defined in Hasql.Pool

Methods

(==) :: UsageError -> UsageError -> Bool

(/=) :: UsageError -> UsageError -> Bool

type ConnectionGetter = IO (Either ConnectionError Connection)

Connection getter action that allows for obtaining Postgres connection settings via external resources such as AWS tokens etc.

data Stats

Constructors

Stats

Fields

• currentUsage :: !Int

  Current number of items.

• available :: !Int

  Total items available for consumption.

Instances

Show Stats

Defined in Hasql.Pool

Methods

showsPrec :: Int -> Stats -> ShowS

show :: Stats -> String

showList :: [Stats] -> ShowS

stats :: Pool -> IO Stats

getPoolUsageStat :: Pool -> IO PoolSize

acquire :: Settings -> IO Pool

Given the pool-size, timeout and connection settings create a connection-pool.

acquireWith :: ConnectionGetter -> Settings -> IO Pool

Similar to acquire, allows for finer configuration.

release :: Pool -> IO ()

Release the connection-pool by closing and removing all connections.

use :: Pool -> Session a -> IO (Either UsageError a)

Use a connection from the pool to run a session and return the connection to the pool, when finished.

useWithObserver :: Maybe ObserverAction -> Pool -> Session a -> IO (Either UsageError a)

Same as use but allows for a custom observer action. You can use it for gathering latency metrics.

withResourceOnEither :: Pool resource -> (resource -> IO (Either failure success)) -> IO (Either failure success)