ElasticSearch7.3|ElasticSearch7.3 学习之生产环境实时重建索引

1、实时重建索引
【ElasticSearch7.3|ElasticSearch7.3 学习之生产环境实时重建索引】在实际的生产环境中,一个field的设置是不能被修改的,如果要修改一个Field,那么应该重新按照新的mapping,建立一个index,然后将数据批量查询出来,重新用bulk api写入index中。
批量查询的时候,建议采用scroll api,并且采用多线程并发的方式来reindex数据。例如说每次scoll就查询指定日期的一段数据,交给一个线程即可。
(1) 一开始,依靠dynamic mapping,插入数据,但是不小心有些数据是2019-09-10这种日期格式的,所以title这种field被自动映射为了date类型,实际上它应该是string类型的。
首先插入以下数据

PUT /my_index/_doc/1 { "title": "2019-09-10" }PUT /my_index/_doc/2 { "title": "2019-09-11" }

(2)当后期向索引中加入string类型的title值的时候,就会报错
PUT /my_index/_doc/3 { "title": "my first article" }

报错
{ "error": { "root_cause": [ { "type": "mapper_parsing_exception", "reason": "failed to parse field [title] of type [date] in document with id '3'. Preview of field's value: 'my first article'" } ], "type": "mapper_parsing_exception", "reason": "failed to parse field [title] of type [date] in document with id '3'. Preview of field's value: 'my first article'", "caused_by": { "type": "illegal_argument_exception", "reason": "failed to parse date field [my first article] with format [strict_date_optional_time||epoch_millis]", "caused_by": { "type": "date_time_parse_exception", "reason": "Failed to parse with all enclosed parsers" } } }, "status": 400 }

(3)如果此时想修改title的类型,是不可能的
PUT /my_index/_mapping { "properties": { "title": { "type": "text" } } }

报错
{ "error": { "root_cause": [ { "type": "illegal_argument_exception", "reason": "mapper [title] of different type, current_type [date], merged_type [text]" } ], "type": "illegal_argument_exception", "reason": "mapper [title] of different type, current_type [date], merged_type [text]" }, "status": 400 }

(4)此时,唯一的办法,就是进行reindex,也就是说,重新建立一个索引,将旧索引的数据查询出来,再导入新索引。
(5)如果说旧索引的名字,是old_index,新索引的名字是new_index,终端java应用,已经在使用old_index在操作了,难道还要去停止java应用,修改使用的indexnew_index,才重新启动java应用吗?这个过程中,就会导致java应用停机,可用性降低。
(6)所以说,给java应用一个别名,这个别名是指向旧索引的,java应用先用着,java应用先用prod_index来操作,此时实际指向的是旧的my_index
PUT /my_index/_alias/prod_index

(7)查看别名,会发现my_index已经存在一个别名prod_index了。
GET my_index/_alias

(8)新建一个index,调整其title的类型为string
PUT /my_index_new { "mappings": { "properties": { "title": { "type": "text" } } } }

(9)使用scroll api将数据批量查询出来
GET /my_index/_search?scroll=1m { "query": { "match_all": {} }, "size": 1 }

返回
{ "_scroll_id" : "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAAARUMWQWx5bzRmTW9TeUNpNmVvN0E2dF9YQQ==", "took" : 4, "timed_out" : false, "_shards" : { "total" : 1, "successful" : 1, "skipped" : 0, "failed" : 0 }, "hits" : { "total" : { "value" : 2, "relation" : "eq" }, "max_score" : 1.0, "hits" : [ { "_index" : "my_index", "_type" : "_doc", "_id" : "1", "_score" : 1.0, "_source" : { "title" : "2019-09-10" } } ] } }

(9)采用bulk apiscoll查出来的一批数据,批量写入新索引
POST /_bulk {"index":{"_index":"my_index_new","_id":"1"}} {"title":"2019-09-10"}

(10)反复循环8~9,查询一批又一批的数据出来,采取bulk api将每一批数据批量写入新索引
(11)将my_index索引的别名prod_index切换到my_index_new上去,java应用会直接通过index别名使用新的索引中的数据,java应用程序不需要停机,零提交,高可用
POST /_aliases { "actions": [ { "remove": { "index": "my_index", "alias": "prod_index" } }, { "add": { "index": "my_index_new", "alias": "prod_index" } } ] }

(12)直接通过prod_index别名来查询,是否ok
GET prod_index/_search

可以看到能够查询到新索引my_index_new的数据了
{ "took" : 1117, "timed_out" : false, "_shards" : { "total" : 1, "successful" : 1, "skipped" : 0, "failed" : 0 }, "hits" : { "total" : { "value" : 1, "relation" : "eq" }, "max_score" : 1.0, "hits" : [ { "_index" : "my_index_new", "_type" : "_doc", "_id" : "1", "_score" : 1.0, "_source" : { "title" : "2019-09-10" } } ] } }

2、总结:
基于aliasclient透明切换index
PUT /my_index_v1/_alias/my_index

clientmy_index进行操作
reindex操作,完成之后,切换v1到v2
POST /_aliases { "actions": [ { "remove": { "index": "my_index_v1", "alias": "my_index" }}, { "add":{ "index": "my_index_v2", "alias": "my_index" }} ] }

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