大致有三种解决方法
- scan and scroll all documents
- _update_by_query api
- re-index and add new fields, use the /_reindex API
首先要设置允许script运行，修改elasticsearch.yml

script.engine.groovy.inline.aggs: on
script.engine.groovy.inline.search: on
script.engine.groovy.inline.update: on

或者

script.inline: true

scan anc scroll all documents
use /_search?scroll to fetch the docs
perform your operation
send /_bulk update requests

POST bt/bt/_update
{
    "script" : "ctx._source.new_field = \"value_of_new_field\""
}

_update_by_query API

POST bt/bt/_update_by_query
{
  "script": {
    "inline": "if (ctx._source.bt0 == null || ctx._source.bt1==null) { ctx._source.btNew1=null } else { ctx._source.btNew1 = ctx._source.bt0 + ctx._source.bt1 }"
  }
}

reindex
https://www.elastic.co/guide/en/elasticsearch/reference/master/docs-reindex.html

{
  "source": {
    "index": "bt",
    "type": "bt"
  },

  "dest": {
    "index": "new_bt1"
  },
  "script": {
    "inline": "if (ctx._source.bt0 == null || ctx._source.bt1==null) { ctx._source.btPlus=null } else { ctx._source.btPlus = ctx._source.bt0 + ctx._source.bt1 }"
  }
}

Difference between _update_by_query and _reindex
- Just like _update_by_query, _reindex gets a snapshot of the source index but its target must be a different index so version conflicts are unlikely.
- Unlike _update_by_query, the script is allowed to modify the document’s metadata.

其实_update_and_query和_reindex的实现差不多，性能没有测过，不过应该差不多。所以elasticsearch还有task api可以用来检测这两个任务运行情况。

作者：虎耳
链接：https://www.jianshu.com/p/f5a57a2cde58
来源：简书
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。

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