How to check the timezone file version in Oracle

Check the DST timezone file version the database uses. Patch bundles often ship newer versions, and the on-disk file must match the database property.

-- Timezone file version in use
SELECT * FROM v$timezone_file;

-- Database properties (server timezone file version + upgrade state)
SELECT property_name, property_value
FROM   database_properties
WHERE  property_name LIKE 'DST_%';