system.xml text area not saving large data

I have a text area inside system.xml file and it is working fine for small data but for large data, it is not saving and truncating data, maybe there is a DB column length limitation.
How to resolve this since I have to save thousand of comma separated values inside it.

<field id="postcodes" translate="label" type="textarea" sortOrder="20" showInDefault="1" showInWebsite="1" showInStore="1">                
    <label>QR Codes</label>
    <comment>Comma-separated</comment>
    <depends>
        <field id="enable">1</field>
    </depends>
</field>