比如我有以下的文档：
{ "took" : 11, "timed_out" : false, "_shards" : { "total" : 5, "successful" : 5, "skipped" : 0, "failed" : 0 }, "hits" : { "total" : 5, "max_score" : 1.0, "hits" : [ { "_index" : "test", "_type" : "mydoc", "_id" : "XxyrM2kBVzdNcvl_GHv2", "_score" : 1.0, "_source" : { "name" : "Shiled", "twitter" : "Sonny sql is awesome", "date" : "2018-12-27", "id" : 1240, "tags" : [ "red", "shit" ] } }, { "_index" : "test", "_type" : "mydoc", "_id" : "YByrM2kBVzdNcvl_tnvm", "_score" : 1.0, "_source" : { "name" : "YYerk", "twitter" : "sql is awesome", "date" : "2008-12-27", "id" : 12357, "tags" : [ "red" ] } }, { "_index" : "test", "_type" : "mydoc", "_id" : "7777", "_score" : 1.0, "_source" : { "name" : "Rocky Chen", "twitter" : "sql is awesome", "date" : "2008-12-27", "id" : 9999 } }, { "_index" : "test", "_type" : "mydoc", "_id" : "YhzDN2kBVzdNcvl_enuT", "_score" : 1.0, "_source" : { "name" : "YYerk", "twitter" : "sql is awesome", "date" : "2008-12-27", "id" : 888888, "tags" : [ "red", "green" ] } }, { "_index" : "test", "_type" : "mydoc", "_id" : "YxzDN2kBVzdNcvl_u3th", "_score" : 1.0, "_source" : { "name" : "YYerk", "twitter" : "sql is awesome", "date" : "2008-12-27", "id" : 888888, "tags" : [ "red", "green" ] } } ] } }如果我想看看id是 "_id" : "YxzDN2kBVzdNcvl_u3th",
这个文档是保存在哪个分片，如何查看？
引用：
路由一个文档到一个分片中编辑
当索引一个文档的时候，文档会被存储到一个主分片中。 Elasticsearch 如何知道一个文档应该存放到哪个分片中呢？当我们创建文档时，它如何决定这个文档应当被存储在分片 1 还是分片 2 中呢？
首先这肯定不会是随机的，否则将来要获取文档的时候我们就不知道从何处寻找了。实际上，这个过程是根据下面这个公式决定的：
shard = hash(routing) % number_of_primary_shards
routing 是一个可变值，默认是文档的 _id ，也可以设置成一个自定义的值。 routing 通过 hash 函数生成一个数字，然后这个数字再除以 number_of_primary_shards （主分片的数量）后得到 余数 。这个分布在 0 到 number_of_primary_shards-1 之间的余数，就是我们所寻求的文档所在分片的位置。
这就解释了为什么我们要在创建索引的时候就确定好主分片的数量 并且永远不会改变这个数量：因为如果数量变化了，那么所有之前路由的值都会无效，文档也再也找不到了。
那么可以使用
GET test/_search_shards?routing=ID号来查看你要查询的id所在的分片
得到的结果：
{ "nodes" : { "yl-qYmh1SXqzJsfI4d1ddw" : { "name" : "node-3", "ephemeral_id" : "UsJ9rFELTiCW07oHE9YMdg", "transport_address" : "10.18.6.26:9300", "attributes" : { "ml.machine_memory" : "6088101888", "rack" : "r1", "ml.max_open_jobs" : "20", "xpack.installed" : "true", "ml.enabled" : "true" } }, "wT7wUd3iTkujYUsbVNVv-w" : { "name" : "node-1", "ephemeral_id" : "fP-vgSb0SdemnHDyaJUsWw", "transport_address" : "10.18.6.102:9300", "attributes" : { "ml.machine_memory" : "8256720896", "rack" : "r1", "xpack.installed" : "true", "ml.max_open_jobs" : "20", "ml.enabled" : "true" } } }, "indices" : { "test" : { } }, "shards" : [ [ { "state" : "STARTED", "primary" : true, "node" : "wT7wUd3iTkujYUsbVNVv-w", "relocating_node" : null, "shard" : 1, "index" : "test", "allocation_id" : { "id" : "k-8E4dL7QmGgwcsNsUCP6Q" } }, { "state" : "STARTED", "primary" : false, "node" : "yl-qYmh1SXqzJsfI4d1ddw", "relocating_node" : null, "shard" : 1, "index" : "test", "allocation_id" : { "id" : "lvOpQIKgRUibkulr3nRfEw" } } ] ] }只需要关注shards字段就可以，从上面可以看到，该文档存在shard 1 主分片上。
原文链接：
http://30daydo.com/article/493
