I've found answer while carefully read again the admin guide's "Managing storage for historical data" section.

I found the answer while carefully reading again the admin guide's "Managing storage for historical data" section:

Over time, the recorded network history will grow unbounded, increasing storage used by the database. Horizon expands the data ingested from stellar-core and needs sufficient disk space. Unless you need to maintain a history archive you may configure Horizon to only retain a certain number of ledgers in the database. This is done using the --history-retention-count flag or the HISTORY_RETENTION_COUNT environment variable. Set the value to the number of recent ledgers you wish to keep around, and every hour the Horizon subsystem will reap expired data. Alternatively, you may execute the command horizon db reap to force a collection.