Database.MongoDB.Connection

A replica set is a set of servers that mirror each other (a non-replicated server can act like a replica set of one). One server in a replica set is the master and the rest are slaves. When the master goes down, one of the slaves becomes master. The ReplicaSet object in this client maintains a list of servers that it currently knows are in the set. It refreshes this list every time it establishes a new connection with one of the servers in the set. Each server in the set knows who the other member in the set are, and who is master. The user asks the ReplicaSet object for a new master or slave connection. When a connection fails, the user must ask the ReplicaSet for a new connection (which most likely will connect to another server since the previous one failed). When connecting to a new server you loose all session state that was stored with the old server, which includes open cursors and temporary map-reduce output collections. Attempting to read from a lost cursor on a new server will raise a ServerFailure exception. Attempting to read a lost map-reduce temp output on a new server will return an empty set (not an error, like it maybe should).

Documentation

runNet :: ErrorT IOError m a -> m (Either IOError a)

Execute action that raises IOError only on network problem. Other IOErrors like file access errors are not caught by this.

Host

data Host

Constructors

Host HostName PortID

Instances

Eq Host

Ord Host

Show Host

data PortID

Constructors

Service String

PortNumber PortNumber

UnixSocket String

Instances

Eq PortID

Ord PortID

Show PortID

host :: HostName -> Host

Host on default MongoDB port

showHostPort :: Host -> String

Display host as "host:port"

readHostPort :: String -> Host

Read string "hostname:port" as Host hostname port or "hostname" as host hostname (default port). Error if string does not match either syntax.

readHostPortM :: Monad m => String -> m Host

Read string "hostname:port" as Host hosthame port or "hostname" as host hostname (default port). Fail if string does not match either syntax.

ReplicaSet

data ReplicaSet

Reference to a replica set of hosts. Ok if really not a replica set and just a stand-alone server, in which case it acts like a replica set of one.

replicaSet :: [Host] -> IO ReplicaSet

Create a reference to a replica set with given hosts as the initial seed list (a subset of the hosts in the replica set)

replicas :: ReplicaSet -> IO [Host]

Return current list of known hosts in replica set. This list is updated on every newConnection.

newConnection :: (Throw IOError m, MonadIO' m) => MasterOrSlaveOk -> ReplicaSet -> m Connection

Create a connection to a master or slave in the replica set. Throw IOError if failed to connect to any host in replica set that is the right master/slave type. close connection when you are done using it even if a failure is raised. Garbage collected connections will be closed automatically (but don't rely on this when creating many connections). TODO: prefer slave over master when SlaveOk and both are available.

MasterOrSlaveOk

data MasterOrSlaveOk

Constructors

Master

connect to master only

SlaveOk

connect to a slave, or master if no slave available

Instances

Eq MasterOrSlaveOk

Show MasterOrSlaveOk

Monad m => Context MasterOrSlaveOk (Connected m)

Connection

type Connection = Pipe Handle ByteString

Thread-safe TCP connection to server with pipelined requests

connect :: (Throw IOError m, MonadIO' m) => Host -> m Connection

Create a connection to the given host (as opposed to connecting to some host in a replica set via newConnection). Throw IOError if can't connect.

Resource

class Resource m r where

Methods

close :: r -> m ()

Close resource

isClosed :: r -> m Bool

Is resource closed

Instances

Resource IO Handle

Conn m => Resource m Cursor

Resource IO h => Resource IO (Pipe h b)