常見的，Elasticsearch常見unassigned原因和解決方式

查看unsigned 的原因

GET /_cluster/health
GET _cluster/allocation/explain?pretty

1、磁盤滿

the node is above the high watermark cluster setting [cluster.routing.allocation.disk.watermark.high=95%], using more disk space than the maximum allowed [95.0%], actual free: [4.055101177689788%]

解決：磁盤擴容或定期刪除無用數據（設定數據保存時間）

DELETE /indexName

通常如果磁盤滿了，ES為了保證集群的穩定性，會將該節點上所有的索引設置為只讀。ES 7.x版本之后當磁盤空間提升后可自動解除，但是7.x版本之前則需要手動執行下面的API來解除只讀模式：

PUT indexName/_settings
{"index": {"blocks": {"read_only_allow_delete": "false"}}
}

2、分配文檔超過最大限制

failure IllegalArgumentException[number of documents in the index cannot exceed 2147483519

常見的？解決：向新索引中寫入數據（按天生成新索引），并設置分片大小

3、主分片所在節點掉線

cannot allocate because a previous copy of the primary shard existed but can no longer be found on the nodes in the cluster

解決：找到掉線的故障原因，并將節點重新加入集群，等待分片恢復

PUT /_cluster/settings
{"transient" : {"cluster.routing.allocation.include._ip": "IP address"}
}

4、索引屬性與節點屬性不匹配

node does not match index setting [index.routing.allocation.require] filters [temperature:“warm”,_id:“comdNq4ZSd2Y6ycB9Oubsg”]

解決：重新設置索引的冷熱屬性，和節點保持一致；如果重新設置節點屬性，則需要重啟節點。可以通過API來修改索引所需要分配節點的溫度屬性

PUT /indexName/_settings
{"index": {"routing": {"allocation": {"require": {"temperature": "warm"}}}}
}

5、節點長時間掉線后再次加入集群，導致引入臟數據

cannot allocate because all found copies of the shard are either stale or corrupt

解決：使用reroute api

PUT /_cluster/reroute
{"commands": [{"allocate_stale_primary": {"index": "IndexName","share": "0","node": "nodeName","accept_data_loss": true}}]
}

elasticsearch should。6、未分配的分片太多，導致達到了分片恢復的最大閾值，其他分片需要排隊等待

reached the limit of incoming shard recoveries [2], cluster setting [cluster.routing.allocation.node_concurrent_incoming_recoveries=2] (can also be set via [cluster.routing.allocation.node_concurrent_recoveries])

解決：使用cluster/settings調大分片恢復的并發度和速度

PUT /_cluster/settings
{"persistent": {"indices.recovery.max_bytes_per_sec": "200mb","cluster.routing.allocation.node_concurrent_recoveries":5,"cluster.routing.allocation.cluster_concurrent_rebalance":5}
}

參考整理自：Elasticsearch集群規劃及性能優化實踐（筆記）