# Requirements for precision tuning to work

**URL:** https://discuss.elastic.co/t/requirements-for-precision-tuning-to-work/364607
**Category:** Elasticsearch
**Created:** [August 8, 2024, 12:49pm UTC](https://discuss.elastic.co/t/requirements-for-precision-tuning-to-work/364607 "2024-08-08T12:49:49Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![tomekred](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/tomekred/32/136635_2.png) [@tomekred](https://discuss.elastic.co/u/tomekred)
#### Post date: [August 8, 2024, 12:49pm UTC](https://discuss.elastic.co/t/requirements-for-precision-tuning-to-work/364607/1 "2024-08-08T12:49:49Z")

</div>

Hello All,

Recently I've been trying to make App Search working on an existing index (and modifying the mapping accordingly) , but I am not sure if I understand the process correctly.  
I would be very pleased if you could answer my questions.

1. If I want to use Precision tuning, do I need to add all listed subfields under the specific text field or can I add only the ones that seems relevant to my use case, eg. prefix only?
2. If I add a subfield named 'prefix' type 'text' under a keyword field - does that mean it will not work with App Search and won't make any difference in search results?
3. Do I have to add those subfields to all text fields or only the ones that I plan on use for search?

I have few large indexes that I would rather modify to work with App Search instead of creating separate ones only for that purpose. The main reason is that they are recreated every night to be up-to-date.  
I store almost all the fields as keyword and add multi-fields to the ones I need more flexibility and doing search on them, so some of the fields has subfields for suggester etc.

I have created a test App Search Engine with a generic json as data and took a look into the mapping to see how it looks like. Then I added just the prefix subfield and relevant analyzers and filter to my own index, created new Engine and tested, and the results seems to be not exactly as I would like to see them.  
The mapping looks like this:

```auto
"some_field": {
    "properties": {
      "value": {
        "type": "keyword",
        "normalizer": "lowercase",
        "fields": {
          "prefix": {
            "type": "text",
            "index_options": "docs",
            "analyzer": "i_prefix",
            "search_analyzer": "q_prefix"
          }
        }
      }
    }
  }

```

I hope you can help me a bit, I just need a point in a direction, before I take any more action to find working strategy.

Thanks and have a great day all!