Package org.elasticsearch.cluster.routing.allocation.allocator

Interface ShardsAllocator

All Known Implementing Classes:
BalancedShardsAllocator
public interface ShardsAllocator

A ShardsAllocator is the main entry point for shard allocation on nodes in the cluster. The allocator makes basic decision where a shard instance will be allocated, if already allocated instances need to relocate to other nodes due to node failures or due to rebalancing decisions.

  • Method Details

    • allocate

      void allocate(RoutingAllocation allocation)
      Allocates shards to nodes in the cluster. An implementation of this method should: - assign unassigned shards - relocate shards that cannot stay on a node anymore - relocate shards to find a good shard balance in the cluster
      Parameters:
      allocation - current node allocation

    • decideShardAllocation

      ShardAllocationDecision decideShardAllocation(ShardRouting shard, RoutingAllocation allocation)
      Returns the decision for where a shard should reside in the cluster. If the shard is unassigned, then the AllocateUnassignedDecision will be non-null. If the shard is not in the unassigned state, then the MoveDecision will be non-null. This method is primarily used by the cluster allocation explain API to provide detailed explanations for the allocation of a single shard. Implementations of the allocate(RoutingAllocation) method may use the results of this method implementation to decide on allocating shards in the routing table to the cluster. If an implementation of this interface does not support explaining decisions for a single shard through the cluster explain API, then this method should throw a UnsupportedOperationException.