What indexes are created when indexing a document in elasticsearch

Question

If I create a first document of it's type, or put a mapping, is an index created for each field?

Obviously if i set "index" to "analyzed" or "not analyzed" the field is indexed.

Is there a way to store a field so it can be retrieved but never searched by? I imagine this will save a lot of space? If I set this to "no" will this save space?

Will I still be able to search by this, just take more time, or will this be totally unsearchable?

Is there a way to make a field indexed after some documents are inserted and I change my mind?

For example, I might have a mapping:

{
 "book":{"properties":{
     "title":{"type":"string", "index":"not_analyzed"},
     "shelf":{"type":"long","index":"no"}
}}}

so I want to be able to search by title, but also retrieve the shelf the book is on

Geert-Jan · Accepted Answer · 2013-05-08 18:19:21Z

1

index:no will indeed not create an index for that field, so that saves some space. Once you've done that you can't search for that particular field anymore.

Perhaps also useful in this context is to know aboutthe _source field, which is returned by default and includes all fields you've stored. http://www.elasticsearch.org/guide/reference/mapping/source-field/

As to your second question: you can't change your mind halfway. When you want to index a particular field later on you have to reindex the documents.

That's why you may want to reconsider setting index:no, etc. In fact a good strategy to begin is to don't define a schema for fields at all, unless you're 100% sure you need a non-default analyzer for a particular field for instance. Otherwise ES will use generally usable defaults.

answered May 8, 2013 at 18:19

Geert-Jan

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4 Comments

eran Over a year ago

Thanks! Can i do it the other way around? Iv told him to index a field but want to erase the index, but still be able to restore the value. The usecase is that i have a url as a field, and indexing this seems silly.

Geert-Jan Over a year ago

Perhaps it's semantics but I'm not sure I understand. If you index a field and then want to erase the index afterwards you can't. Instead you have to decide upfront to not index the field at all. You can still retrieve the value (when you store the field explicitly or even without doing that, since it's by default part of _source . If you mean you want to still search by the field without an index, then no: that's what indices are for. You can't have your cake and eat it too :)

eran Over a year ago

You've answered my question. There are two scenarios: 1. I start out indexing the field but then deciding I don't need to search by it. 2. I start out not indexing the field, then discovering that I want to search by it, and so want to index it In both cases this will require remapping the doc_type and reindexing, as I understood from you. Thanks!!!

Geert-Jan Over a year ago

Indeed. My advice go with option 1. If in the future you happen to have an index for a field you're not searching for, ask yourself: "so what?" Disk space is cheap, and an unused index doesn't take up RAM.

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