有时候可以通过批量操作来减少网络请求。如：批量查询、批量插入数据。

批量查询_mget

＃　当查询的数据都存在时
POST　/test/user/_mget

＃　请求数据
{
    "ids": [
        "1002",
        "1003"
    ]
}

＃　响应结果
{
    "docs": [
        {
            "_index": "test",
            "_type": "user",
            "_id": "1002",
            "_version": 5,
            "_seq_no": 10,
            "_primary_term": 1,
            "found": true,
            "_source": {
                "id": 1002,
                "name": "李四",
                "age": 23,
                "sex": "女"
            }
        },
        {
            "_index": "test",
            "_type": "user",
            "_id": "1003",
            "_version": 1,
            "_seq_no": 11,
            "_primary_term": 1,
            "found": true,
            "_source": {
                "id": 1003,
                "name": "王五",
                "age": 27,
                "sex": "男"
            }
        }
    ]
}

当某一条数据不存在，不影响整体响应，需要通过found的值进行判断是否查询到数据。 

＃　当查询的数据有不存在的时候
POST　/test/user/_mget
＃　请求数据
{
    "ids": [
        "1002",
        "1007"
    ]
}


＃　响应结果
{
    "docs": [
        {
            "_index": "test",
            "_type": "user",
            "_id": "1002",
            "_version": 5,
            "_seq_no": 10,
            "_primary_term": 1,
            "found": true,
            "_source": {
                "id": 1002,
                "name": "李四",
                "age": 23,
                "sex": "女"
            }
        },
        {
            "_index": "test",
            "_type": "user",
            "_id": "1007",
            "found": false
        }
    ]
}

_bulk操作

        在Elasticsearch中，支持批量的插入、修改、删除操作，都是通过_bulk的api完成的。 请求格式如下：（请求格式不同寻常）

{ action: { metadata }}\n 
{ request body }\n 
{ action: { metadata }}\n 
{ request body }\n 
...

批量插入数据：

{"create":{"_index":"test","_type":"user","_id":2001}} 
{"id":2001,"name":"name1","age": 20,"sex": "男"} 
{"create":{"_index":"test","_type":"user","_id":2002}} 
{"id":2002,"name":"name2","age": 20,"sex": "男"} 
{"create":{"_index":"test","_type":"user","_id":2003}} 
{"id":2003,"name":"name3","age": 20,"sex": "男"}

注意：最后一行要有一个回车。

POST　/test/user/_bulk

＃请求数据
{"create":{"_index":"test","_type":"user","_id":2001}} 
{"id":2001,"name":"name1","age": 20,"sex": "男"} 
{"create":{"_index":"test","_type":"user","_id":2002}} 
{"id":2002,"name":"name2","age": 20,"sex": "男"} 
{"create":{"_index":"test","_type":"user","_id":2003}} 
{"id":2003,"name":"name3","age": 20,"sex": "男"}


＃　响应结果
{
    "took": 12,
    "errors": false,
    "items": [
        {
            "create": {
                "_index": "test",
                "_type": "user",
                "_id": "2001",
                "_version": 1,
                "result": "created",
                "_shards": {
                    "total": 2,
                    "successful": 1,
                    "failed": 0
                },
                "_seq_no": 13,
                "_primary_term": 1,
                "status": 201
            }
        },
        {
            "create": {
                "_index": "test",
                "_type": "user",
                "_id": "2002",
                "_version": 1,
                "result": "created",
                "_shards": {
                    "total": 2,
                    "successful": 1,
                    "failed": 0
                },
                "_seq_no": 14,
                "_primary_term": 1,
                "status": 201
            }
        },
        {
            "create": {
                "_index": "test",
                "_type": "user",
                "_id": "2003",
                "_version": 1,
                "result": "created",
                "_shards": {
                    "total": 2,
                    "successful": 1,
                    "failed": 0
                },
                "_seq_no": 15,
                "_primary_term": 1,
                "status": 201
            }
        }
    ]
}

 批量删除

{"delete":{"_index":"test","_type":"user","_id":2001}} 
{"delete":{"_index":"test","_type":"user","_id":2002}} 
{"delete":{"_index":"test","_type":"user","_id":2003}}

POST　/test/user/_bulk

＃　请求数据
{"delete":{"_index":"test","_type":"user","_id":2001}} 
{"delete":{"_index":"test","_type":"user","_id":2002}} 
{"delete":{"_index":"test","_type":"user","_id":2003}}


＃　响应数据
{
    "took": 11,
    "errors": false,
    "items": [
        {
            "delete": {
                "_index": "test",
                "_type": "user",
                "_id": "2001",
                "_version": 2,
                "result": "deleted",
                "_shards": {
                    "total": 2,
                    "successful": 1,
                    "failed": 0
                },
                "_seq_no": 16,
                "_primary_term": 1,
                "status": 200
            }
        },
        {
            "delete": {
                "_index": "test",
                "_type": "user",
                "_id": "2002",
                "_version": 2,
                "result": "deleted",
                "_shards": {
                    "total": 2,
                    "successful": 1,
                    "failed": 0
                },
                "_seq_no": 17,
                "_primary_term": 1,
                "status": 200
            }
        },
        {
            "delete": {
                "_index": "test",
                "_type": "user",
                "_id": "2003",
                "_version": 2,
                "result": "deleted",
                "_shards": {
                    "total": 2,
                    "successful": 1,
                    "failed": 0
                },
                "_seq_no": 18,
                "_primary_term": 1,
                "status": 200
            }
        }
    ]
}

ElasticSearch一次请求多少性能最高？

• 整个批量请求需要被加载到接受我们请求节点的内存里，所以请求越大，给其它请求可用的内存就越小。有一 个最佳的bulk请求大小。超过这个大小，性能不再提升而且可能降低。
• 最佳大小，当然并不是一个固定的数字。它完全取决于你的硬件、你文档的大小和复杂度以及索引和搜索的负 载。
• 幸运的是，这个最佳点(sweetspot)还是容易找到的：试着批量索引标准的文档，随着大小的增长，当性能开始 降低，说明你每个批次的大小太大了。开始的数量可以在1000~5000个文档之间，如果你的文档非常大，可以使用较小的批次。
• 通常着眼于你请求批次的物理大小是非常有用的。一千个1kB的文档和一千个1MB的文档大不相同。一个好的 批次最好保持在5-15MB大小间。