# Keyword subfield of a text field which has high cardinality
**URL:** https://discuss.elastic.co/t/keyword-subfield-of-a-text-field-which-has-high-cardinality/231599
**Category:** Elasticsearch
**Created:** [May 7, 2020, 5:42pm UTC](https://discuss.elastic.co/t/keyword-subfield-of-a-text-field-which-has-high-cardinality/231599 "2020-05-07T17:42:41Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@lloadingll](https://discuss.elastic.co/u/lloadingll)
#### Post date: [May 7, 2020, 5:42pm UTC](https://discuss.elastic.co/t/keyword-subfield-of-a-text-field-which-has-high-cardinality/231599/1 "2020-05-07T17:42:41Z")
Hi all,
we have a large amount of data, one of its fields is 'email subject' which is 'text' type. Recently I want to do aggregation by this field on a small subset of the data
(assume after the query filter there are 100K hits to aggregate).
so I plan to modify the field to something like:
```auto
"Subject": {
"type": "text",
"fields": {
"Raw": {
"type": "keyword"
}
}
}
```
And then aggregate by Subject.Raw
I know it's ok for normal fields. But as email titles can be pretty long and have a large cardinality, I'm worried about whether using 'keyword' there will cause some kind of memory overflow, etc.
I guess when querying, 100K hits may not be a problem as it's pretty small. But is there any risk when Elasticsearch do things like building index on this long and high-cardinality 'keyword' field and the total amount is huge?
Maybe I can use 'ignore\_above' to limit the keyword length... then how about the cardinality?
Thanks a lot!
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [June 4, 2020, 5:42pm UTC](https://discuss.elastic.co/t/keyword-subfield-of-a-text-field-which-has-high-cardinality/231599/2 "2020-06-04T17:42:47Z")
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