com.allanbank.mongodb.connection.state

Class ClusterState

java.lang.Object

com.allanbank.mongodb.connection.state.ClusterState

All Implemented Interfaces:

Closeable, AutoCloseable

public class ClusterState
extends Object
implements Closeable

ClusterState tracks the state of the cluster of MongoDB servers. PropertyChangeEvents are fired when a server is added or marked writable/not writable.

This class uses brute force synchronization to protect its internal state. It is assumed that multiple connections will be concurrently updating the ClusterState at once and that at any given time this class may not contain the absolute truth about the state of the cluster. Instead connections should keep querying for the state of the cluster via their connection until the view the server returned and the ClusterState are consistent. Since this class will not fire a PropertyChangeEvent when the state is not truly modified the simplest mechanism is to keep querying for the cluster state on the connection until no addition change events are seen.

API Warning:

This class is NOT part of the drivers API. This class may be mutated in incompatible ways between any two releases of the driver.

Copyright ©:

2011-2013, Allanbank Consulting, Inc., All Rights Reserved

Field Summary

Fields

Modifier and Type	Field and Description
protected ConcurrentMap<String,ServerState>	myServers The complete list of servers.

Constructor Summary

Constructors

Constructor and Description
ClusterState(MongoClientConfiguration config) Creates a new CLusterState.

Method Summary

Methods

Modifier and Type	Method and Description
ServerState	add(String address) Adds a ServerState to the ClusterState for the address provided if one does not already exist.
void	addListener(PropertyChangeListener listener) Adds a listener to the state.
protected double[]	cdf(List<ServerState> servers) Computes a relative CDF (cumulative distribution function) for the servers based on the latency from the client.
void	close()
protected List<ServerState>	findCandidateServer(ReadPreference readPreference) Finds the candidate server, if known.
List<ServerState>	findCandidateServers(ReadPreference readPreference) Returns the set of servers that can be used based on the provided ReadPreference.
protected List<ServerState>	findNearestCandidates(ReadPreference readPreference) Returns the list of servers that match the read preference's tags.
protected List<ServerState>	findNonWritableCandidates(ReadPreference readPreference) Returns the list of non-writable servers that match the read preference's tags.
protected List<ServerState>	findWritableCandidates(ReadPreference readPreference) Returns the list of writable servers that match the read preference's tags.
ServerState	get(String address) Returns the server state for the address provided.
List<ServerState>	getNonWritableServers() Returns a copy of the list of non-writable servers.
List<ServerState>	getServers() Returns a copy of the list of servers.
List<ServerState>	getWritableServers() Returns a copy of the list of writable servers.
void	markNotWritable(ServerState server) Marks the server as non-writable.
void	markWritable(ServerState server) Marks the server as writable.
void	removeListener(PropertyChangeListener listener) Removes a listener to the state.
protected void	sort(List<ServerState> servers) Sorts the servers based on the latency from the client.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

myServers

protected final ConcurrentMap<String,ServerState> myServers

The complete list of servers.

Constructor Detail

ClusterState

public ClusterState(MongoClientConfiguration config)

Creates a new CLusterState.

Parameters:

config - The configuration for the cluster.

Method Detail

add

public ServerState add(String address)

Adds a ServerState to the ClusterState for the address provided if one does not already exist.

This method is equivalent to calling get(String).

Parameters:

address - The address of the ServerState to return.

Returns:

The ServerState for the address.

addListener

public void addListener(PropertyChangeListener listener)

Adds a listener to the state.

Parameters:

listener - The listener for the state changes.

close

public void close()

Overridden to ensure all of the ServerState connections are closed.

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

findCandidateServers

public List<ServerState> findCandidateServers(ReadPreference readPreference)

Returns the set of servers that can be used based on the provided ReadPreference.

Parameters:

readPreference - The ReadPreference to filter the servers.

Returns:

The List of servers that can be used. Servers will be ordered by preference to be used, most preferred to least preferred.

get

public ServerState get(String address)

Returns the server state for the address provided. If the ServerState does not already exist a non-writable state is created and returned.

Parameters:

address - The address of the ServerState to return.

Returns:

The ServerState for the address.

getNonWritableServers

public List<ServerState> getNonWritableServers()

Returns a copy of the list of non-writable servers. The list returned is a copy of the internal list and can be modified by the caller.

Returns:

The complete list of non-writable servers.

getServers

public List<ServerState> getServers()

Returns a copy of the list of servers. The list returned is a copy of the internal list and can be modified by the caller.

Returns:

The complete list of servers.

getWritableServers

public List<ServerState> getWritableServers()

Returns a copy of the list of writable servers. The list returned is a copy of the internal list and can be modified by the caller.

Returns:

The complete list of writable servers.

markNotWritable

public void markNotWritable(ServerState server)

Marks the server as non-writable. Fires a PropertyChangeEvent if the server was previously writable.

Parameters:

server - The server to mark non-writable.

markWritable

public void markWritable(ServerState server)

Marks the server as writable. Fires a PropertyChangeEvent if the server was previously non-writable.

Parameters:

server - The server to mark writable.

removeListener

public void removeListener(PropertyChangeListener listener)

Removes a listener to the state.

Parameters:

listener - The listener for the state changes.

cdf

protected final double[] cdf(List<ServerState> servers)

Computes a relative CDF (cumulative distribution function) for the servers based on the latency from the client.

The latency of each server is used to create a strict ordering of servers from lowest latency to highest. The relative latency of the i'th server is then calculated based on the function:

                                       latency[0]
                relative_latency[i] =  ----------
                                       latency[i]
 

The relative latencies are then then summed and the probability of selecting each server is then calculated by:

                                  relative_latency[i]
     probability[i] = -------------------------------------------------
                      sum(relative_latency[0], ... relative_latency[n])
 

The CDF over these probabilities is returned.

Parameters:

servers - The servers to compute the CDF for.

Returns:

The CDF for the server latencies.

findCandidateServer

protected List<ServerState> findCandidateServer(ReadPreference readPreference)

Finds the candidate server, if known.

Parameters:

readPreference - The read preference to match the server against.

Returns:

The Server found in a singleton list or an empty list if the server is not known.

findNearestCandidates

protected List<ServerState> findNearestCandidates(ReadPreference readPreference)

Returns the list of servers that match the read preference's tags.

Parameters:

readPreference - The read preference to match the server against.

Returns:

The servers found in order of preference. Generally this is in latency order but we randomly move one of the servers to the front of the list to distribute the load across more servers.

See Also:

sort(java.util.List<com.allanbank.mongodb.connection.state.ServerState>)

findNonWritableCandidates

protected List<ServerState> findNonWritableCandidates(ReadPreference readPreference)

Returns the list of non-writable servers that match the read preference's tags.

Parameters:

readPreference - The read preference to match the server against.

Returns:

The servers found in order of preference. Generally this is in latency order but we randomly move one of the servers to the front of the list to distribute the load across more servers.

See Also:

sort(java.util.List<com.allanbank.mongodb.connection.state.ServerState>)

findWritableCandidates

protected List<ServerState> findWritableCandidates(ReadPreference readPreference)

Returns the list of writable servers that match the read preference's tags.

Parameters:

readPreference - The read preference to match the server against.

Returns:

The servers found in order of preference. Generally this is in latency order but we randomly move one of the servers to the front of the list to distribute the load across more servers.

See Also:

sort(java.util.List<com.allanbank.mongodb.connection.state.ServerState>)

sort

protected final void sort(List<ServerState> servers)

Sorts the servers based on the latency from the client.

To distribute the requests across servers more evenly the first server is replaced with a random server based on a single sided simplified Gaussian distribution.

Parameters:

servers - The servers to be sorted.

See Also:

cdf(List)