Package org.apache.solr.cluster.placement

This package contains interfaces visible by plugins (i.e. contributed code) implementing cluster elasticity, placement and scalability, as well as a few examples on how plugins can be implemented.

Initially, only placement related plugins are supported.

The entry point is the PlacementPluginFactory building instances of the PlacementPlugin interface where the placement computation is implemented.

From there, one will access the interfaces that allow navigating the cluster topology, see org.apache.solr.cluster.

Plugin code:

• Gets work to be done by receiving a PlacementRequest,
• Can obtain more info using AttributeFetcher and building an AttributeValues
• Uses the values from AttributeValues as well as cluster state and SolrCollection.getCustomProperty(java.lang.String) and other data to compute placement,
• Placement decisions are returned to Solr using an instance of PlacementPlan built using the PlacementPlanFactory

Interface Summary

Interface	Description
AttributeFetcher	Instances of this interface are used to fetch various attributes from nodes (and other sources) in the cluster.
AttributeValues
CollectionMetrics	Collection-level metrics.
DeleteCollectionRequest	Delete collection request.
DeleteReplicasRequest	Delete replicas request.
DeleteShardsRequest	Delete shards request.
Metric<T>	Metric-related attribute of a node or replica.
ModificationRequest	Collection modification request.
NodeMetric<T>	Node metric identifier, corresponding to a node-level metric registry and the internal metric name.
PlacementContext	Placement context makes it easier to pass around and access main placement-related components.
PlacementPlan	A fully specified plan or instructions for placement, deletion or move to be applied to the cluster.
PlacementPlanFactory	Allows plugins to create PlacementPlans telling the Solr layer where to create replicas following the processing of a PlacementRequest.
PlacementPlugin	Implemented by external plugins to control replica placement and movement on the search cluster (as well as other things such as cluster elasticity?) when cluster changes are required (initiated elsewhere, most likely following a Collection API call).
PlacementPluginConfig	Configuration beans should use this interface to define public (mutable) configuration properties.
PlacementPluginFactory<T extends PlacementPluginConfig>	Factory implemented by client code and configured in container plugins (see ContainerPluginsApi.editAPI) allowing the creation of instances of PlacementPlugin to be used for replica placement computation.
PlacementRequest	A cluster related placement request that Solr asks a PlacementPlugin plugin to resolve and compute a PlacementPlan placing one or more Replica's of one or more Shard's of an existing SolrCollection.
ReplicaMetric<T>	Replica metric identifier, corresponding to one of the internal replica-level metric names (as reported in solr.core.[collection].[replica] registry)
ReplicaMetrics	Strongly-typed replica-level metrics.
ReplicaPlacement	Placement decision for a single Replica.
ShardMetrics	Shard-level metrics.

Class Summary

Class	Description
PlacementPluginFactory.NoConfig	Useful type for plugins that don't use any configuration.

Enum Summary

Enum	Description
NodeMetric.Registry	Registry options for node metrics.

Exception Summary

Exception	Description
PlacementException	Exception thrown by a PlacementPlugin when it is unable to compute placement for whatever reason (except an InterruptedException that PlacementPlugin.computePlacement(org.apache.solr.cluster.placement.PlacementRequest, org.apache.solr.cluster.placement.PlacementContext) is also allowed to throw).
PlacementModificationException	Exception thrown when a placement modification is rejected by the placement plugin.