Glossary
SQLite freeblock
Free space inside a SQLite b-tree page, typically left by a deleted record, whose first four bytes are overwritten and the rest left intact.
When a row is deleted, its cell becomes a freeblock chained from the page header. SQLite writes the next-freeblock offset and the block size over the first four bytes and does not clear the rest unless secure_delete is on (file format). Most of the deleted record — for a notification, its XML payload — survives until the space is reused. See recovering deleted notifications.