# FST index

The FST index supports regex queries on text. Decreases on-disk index by 4-6 times. 

* Only supports regex queries
* Only supported on stored or completed Pinot segments (no consuming segments).
* Only supported on dictionary-encoded columns.
* Works better for prefix queries 

{% hint style="info" %}
**Note:** Lucene is case sensitive as such when using FST index based column(s) in query, user needs to ensure this is taken into account. For e.g `Select * from table T where colA LIKE %Value%` which has a FST index on colA will only return rows containing string "Value" but not "value".
{% endhint %}

For more information on the FST construction and code, see [Lucene documentation](https://lucene.apache.org/core/9_10_0/core/org/apache/lucene/util/fst/FST.html).

## Enable the FST index

To enable the FST index on a dictionary-encoded column, include the following configuration:

```javascript
"fieldConfigList":[
{
"name":"text_col_1",
"encodingType":"DICTIONARY",
"indexType":"FST"
}
]
```

The FST index generates one FST index file (`.lucene.fst)`. If the inverted index is enabled, this is further able to take advantage of that.

For more information about enabling the FST index, see ways to [enable indexes](https://docs.pinot.apache.org/release-1.3.0/basics/indexing/..#enabling-indexes).

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