背景说明
执行《Elasticsearch 权威指南》的示例，在执行聚合查询的时候，报错 Fielddata is disabled on text fields by default.
1）聚合语句如下：
GET _search
{
"aggs": {
"all_interests": {
"terms": { "field": "interests"}
}
}
}
2）报错信息如下：
{
"error": {
"root_cause": [
{
"type": "illegal_argument_exception",
"reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [interests] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead."
}
],
"type": "search_phase_execution_exception", "reason": "all shards failed", "phase": "query", "grouped": true, "failed_shards": [ { "shard": 0, "index": "megacorp", "node": "jbFtoSVqQAqfYhE5uTBFvw", "reason": { "type": "illegal_argument_exception", "reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [interests] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead." } } ] }, "status": 400 }
3）Kibana 的 Dev Tools 执行截图如下：
原因分析
Elasticsearch 5.x版本以后，对排序和聚合等操作，用单独的数据结构(fielddata)缓存到内存里了，需要单独开启。
具体请参考：fielddata
解决方案
1）执行如下语句，将 interests字段进行开启映射mapping：
PUT megacorp/_mapping/employee/
{
"properties":{
"interests":{
"type":"text",
"fielddata":true
}
}
}
2）Kibana 的 Dev Tools 中执行开启映射mapping语句，截图如下：
3）再次实行聚合语句，结果如下：
{ "took": 455, "timed_out": false, "_shards": { "total": 5, "successful": 5, "skipped": 0, "failed": 0 }, "hits": { "total": 3, "max_score": 1, "hits": [ { "_index": "megacorp", "_type": "employee", "_id": "2", "_score": 1, "_source": { "first_name": "Jane", "last_name": "Smith", "age": 32, "about": "I like to collect rock albums", "interests": [ "music" ] } }, { "_index": "megacorp", "_type": "employee", "_id": "1", "_score": 1, "_source": { "first_name": "John", "last_name": "Smith", "age": 25, "about": "I love to go rock climbing", "interests": [ "sports" ] } }, { "_index": "megacorp", "_type": "employee", "_id": "3", "_score": 1, "_source": { "first_name": "Douglas", "last_name": "Fir", "age": 35, "about": "I like to build cabinets", "interests": [ "forestry" ] } } ] }, "aggregations": { "all_interests": { "doc_count_error_upper_bound": 0, "sum_other_doc_count": 0, "buckets": [ { "key": "forestry", "doc_count": 1 }, { "key": "music", "doc_count": 1 }, { "key": "sports", "doc_count": 1 } ] } } }
4）Kibana 的 Dev Tools 中，执行效果截图如下：
