【Elasticsearch管理】分片分配

在Elasticsearch中，分片是数据的容器，负责存储部分数据和执行操作。分片可以是主分片或副本分片。分配分片是Elasticsearch集群管理的一个重要部分。

Elasticsearch提供了多种方式来管理分片的分配，例如：

1. 手动分配分片：可以通过Elasticsearch的API手动控制分片的分配。
2. 自动分配分片：Elasticsearch会自动处理分片的分配，例如，在有节点加入或离开集群时。

以下是一个Elasticsearch手动分配分片的例子，使用Elasticsearch的Java High Level REST Client。

import org.elasticsearch.client.RestHighLevelClient;
import org.elasticsearch.client.Requests;
import org.elasticsearch.cluster.routing.allocation.command.MoveAllocationCommand;
import org.elasticsearch.cluster.routing.allocation.command.AllocateEmptyPrimaryAllocationCommand;
import org.elasticsearch.cluster.routing.allocation.command.AllocateStalePrimaryAllocationCommand;
import org.elasticsearch.cluster.routing.allocation.command.CancelAllocationCommand;
import org.elasticsearch.cluster.routing.allocation.command.ShardAllocationCommand;
 
import java.io.IOException;
 
public class ShardAllocationExample {
    public static void main(String[] args) throws IOException {
        try (RestHighLevelClient client = new RestHighLevelClient(...)) {
            // 分配空的主分片
            AllocateEmptyPrimaryAllocationCommand allocateEmptyPrimaryCommand = new AllocateEmptyPrimaryAllocationCommand("index_name", 0, "node_name");
            ShardAllocationCommand command = new ShardAllocationCommand(allocateEmptyPrimaryCommand);
            client.cluster().reroute(Requests.clusterRerouteRequest(command), RequestOptions.DEFAULT);
 
            // 取消分配分片
            CancelAllocationCommand cancelAllocationCommand = new CancelAllocationCommand("index_name", 0);
            command = new ShardAllocationCommand(cancelAllocationCommand);
            client.cluster().reroute(Requests.clusterRerouteRequest(command), RequestOptions.DEFAULT);
 
            // 分配旧的主分片
            AllocateStalePrimaryAllocationCommand allocateStalePrimaryCommand = new AllocateStalePrimaryAllocationCommand("index_name", 0, "node_name");
            command = new ShardAllocationCommand(allocateStalePrimaryCommand);
            client.cluster().reroute(Requests.clusterRerouteRequest(command), RequestOptions.DEFAULT);
 
            // 移动分片到新的节点
            MoveAllocationCommand moveAllocationCommand = new MoveAllocationCommand("index_name", 0, "from_node_name", "to_node_name");
            command = new ShardAllocationCommand(moveAllocationCommand);
            client.cluster().reroute(Requests.clusterRerouteRequ