Free Space in Database Files
In SQLite, when you delete or update data, the space it occupied
in the database file is not immediately reclaimed. Instead, the
space is added to the free-list and made available for reuse by new data.
It would be inefficient to return these pages to the operating system
only to reassign them later. And in practice, deleting a lot of data
doesn't usually happen during normal operation.
In exceptional cases, there may be a reason to reorganize the database
file. Sqlite therefore provides the command
vacuum
The HTTP API command <db>/rebuild_db executes it.
It is recommended to stop all applications
and make a backup before.