Mapping Explosion in Nested Datatype

Elastic Stack Elasticsearch
1

The documentation for nested datatype (https://www.elastic.co/guide/en/elasticsearch/reference/current/nested.html) says that in order to prevent mapping explosion the number of nested fields per index is limited to 50. But one can override that by changing the default setting.

I am in the process of creating an index that can have a lot of nested documents. My document structure will look something like:

{
  "personid": 1,
  "comments":[
    {},
    {},
    {},
    ...
  ]
}

Each person can have multiple comments, is each comment considered it's own nested document? What problems will I run into if I set up a person index where each document can have as many as 10,000 comments per person?

Thanks.

2

Having documents containing a lot of nested components can make updates quite expensive. Each nested component of a document is indexed as a separate document behind the scenes, and when anything is updated these are all updated/reindexed. If you have a relatively static dataset this maybe fine, but you may want to consider breaking up and flattening parts of your data model.

3

@Christian_Dahlqvist Thanks for the response. Would having a lot of nested documents in the index affect query performance?

My dataset is not completely static but it does not change a lot either. The personid field is also the document id. I was thinking of replacing the entire document whenever a comment gets added to a person document. Is this a very unreasonable/un-maintainable approach?

4

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