com.bigdata.rdf.sail.webapp.lbs

Class AbstractHostLBSPolicy

java.lang.Object

com.bigdata.rdf.sail.webapp.lbs.AbstractLBSPolicy

com.bigdata.rdf.sail.webapp.lbs.AbstractHostLBSPolicy

All Implemented Interfaces:

QuorumListener, IHALoadBalancerPolicy, IHAPolicyLifeCycle, Serializable

Direct Known Subclasses:

CountersLBSPolicy, GangliaLBSPolicy

public abstract class AbstractHostLBSPolicy
extends AbstractLBSPolicy

Abstract base class for an LBS policy that uses per-host load metrics.

Author:

Bryan Thompson

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	AbstractHostLBSPolicy.InitParams

Field Summary

Fields inherited from class com.bigdata.rdf.sail.webapp.lbs.AbstractLBSPolicy

journalRef, serviceIDRef, serviceTableRef

Constructor Summary

Constructors

Constructor and Description
AbstractHostLBSPolicy()

Method Summary

Methods

Modifier and Type	Method and Description
protected boolean	conditionallyForwardReadRequest(HALoadBalancerServlet servlet, javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response) Hook provides the IHALoadBalancerPolicy with an opportunity to forward a read-request to the local service rather than proxying the request to a service selected by the load balancer (a local forward has less overhead than proxying to either the local host or a remote service, which makes it more efficient under some circumstances to handle the read-request on the service where it was originally received).
protected void	conditionallyUpdateServiceTable() Extended to conditionally update the hostTableRef iff it does not exist or is empty.
void	destroy() Destroy the policy (stop any asynchronous processing, release any resources).
protected abstract String	getDefaultScoringRule() Return the name of the IHostScoringRule that provides default value for the AbstractHostLBSPolicy.InitParams.HOST_SCORING_RULE configuration parameter.
protected long	getHostDiscoveryDelay() The delay between discovery cycles that updates our local knowledge of the load on each host.
protected abstract Map<String,IHostMetrics>	getHostReportForKnownServices(IHostScoringRule scoringRule, ServiceScore[] serviceScores) Return a map from the known canonical hostnames (as self-reported by the services) of the joined services to the IHostMetricss for those hosts.
String	getReaderURI(javax.servlet.http.HttpServletRequest req) Return the Request-URL to which a read-only request will be proxied.
void	init(javax.servlet.ServletConfig servletConfig, IIndexManager indexManager) Initialize the policy.
void	setLocalForwardThreshold(double newValue)
protected void	toString(StringBuilder sb) Extension hook for AbstractLBSPolicy.toString() - implementation MUST NOT block.
protected void	updateHostTable() Update the per-host scoring table.
protected void	updateServiceTable() Overridden to also update the hosts table in case we add/remove a service and the set of hosts that cover the member services is changed as a result.

Methods inherited from class com.bigdata.rdf.sail.webapp.lbs.AbstractLBSPolicy

getJournal, getLeaderURI, getLocalServiceScore, getServiceScoreForHostname, notify, service, toString

Methods inherited from class java.lang.Object

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

Constructor Detail

AbstractHostLBSPolicy

public AbstractHostLBSPolicy()

Method Detail

getDefaultScoringRule

protected abstract String getDefaultScoringRule()

Return the name of the IHostScoringRule that provides default value for the AbstractHostLBSPolicy.InitParams.HOST_SCORING_RULE configuration parameter.

Note: The policy needs to be specific to the LBS implementation since the names of the host metrics depend on the system that is being used to collect and report them.

getHostDiscoveryDelay

protected long getHostDiscoveryDelay()

The delay between discovery cycles that updates our local knowledge of the load on each host.

See Also:

AbstractHostLBSPolicy.InitParams.HOST_DISCOVERY_DELAY

toString

protected void toString(StringBuilder sb)

Description copied from class: AbstractLBSPolicy

Extension hook for AbstractLBSPolicy.toString() - implementation MUST NOT block.

Overrides:

toString in class AbstractLBSPolicy

Parameters:

sb - Buffer where you can write additional state.

init

public void init(javax.servlet.ServletConfig servletConfig,
        IIndexManager indexManager)
          throws javax.servlet.ServletException

Description copied from interface: IHAPolicyLifeCycle

Initialize the policy.

Specified by:

init in interface IHAPolicyLifeCycle

Overrides:

init in class AbstractLBSPolicy

Throws:

javax.servlet.ServletException

destroy

public void destroy()

Description copied from interface: IHAPolicyLifeCycle

Destroy the policy (stop any asynchronous processing, release any resources).

Specified by:

destroy in interface IHAPolicyLifeCycle

Overrides:

destroy in class AbstractLBSPolicy

setLocalForwardThreshold

public void setLocalForwardThreshold(double newValue)

conditionallyUpdateServiceTable

protected void conditionallyUpdateServiceTable()

Extended to conditionally update the hostTableRef iff it does not exist or is empty.

Overrides:

conditionallyUpdateServiceTable in class AbstractLBSPolicy

updateServiceTable

protected void updateServiceTable()

Overridden to also update the hosts table in case we add/remove a service and the set of hosts that cover the member services is changed as a result.

Overrides:

updateServiceTable in class AbstractLBSPolicy

See Also:

AbstractLBSPolicy.serviceTableRef

updateHostTable

protected void updateHostTable()

Update the per-host scoring table. The host table will only contain entries for hosts associated with at least one service that is joined with the met quorum.

See Also:

hostTableRef

getReaderURI

public String getReaderURI(javax.servlet.http.HttpServletRequest req)

Description copied from interface: IHALoadBalancerPolicy

Return the Request-URL to which a read-only request will be proxied. The returned URL must include the protocol, hostname and port (if a non-default port will be used) as well as the target request path.

Parameters:

req - The request.

Returns:

The proxyTo Request-URI -or- null if we could not find a service to which we could proxy this request.

conditionallyForwardReadRequest

protected boolean conditionallyForwardReadRequest(HALoadBalancerServlet servlet,
                                      javax.servlet.http.HttpServletRequest request,
                                      javax.servlet.http.HttpServletResponse response)
                                           throws IOException

Hook provides the IHALoadBalancerPolicy with an opportunity to forward a read-request to the local service rather than proxying the request to a service selected by the load balancer (a local forward has less overhead than proxying to either the local host or a remote service, which makes it more efficient under some circumstances to handle the read-request on the service where it was originally received).

If the normalized availability for this host is over a configured threshold, then we forward the request to the local service. This help to reduce the latency of the request since it is not being proxied.

Overrides:

conditionallyForwardReadRequest in class AbstractLBSPolicy

Throws:

IOException

See Also:

AbstractHostLBSPolicy.InitParams.LOCAL_FORWARD_THRESHOLD

getHostReportForKnownServices

protected abstract Map<String,IHostMetrics> getHostReportForKnownServices(IHostScoringRule scoringRule,
                                                     ServiceScore[] serviceScores)

Return a map from the known canonical hostnames (as self-reported by the services) of the joined services to the IHostMetricss for those hosts.

Parameters:

scoringRule - The IHostScoringRule to be applied.

serviceScores - The set of known services.

Returns:

The map. TODO If there is more than one service on the same host, then we will have one record per host, not per service. This means that we can not support JVM specific metrics, such as GC time. This could be fixed if the map was indexed by Service UUID and the host metrics were combined into the map once for each service.